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new article DSP-speech-decoder
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 29 Oct 2024 22:11:41 +0000
parents 2ac06a49dfbc
children
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a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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1 Rohde & Schwarz CMU200 instrument is an absolutely essential piece of test
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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2 equipment for anyone in the business (or hobby) of designing and building his
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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3 or her own personal cellphones of 2G and/or 3G variety. I (Mother Mychaela)
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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4 currently only work with GSM, but depending on installed hw and sw options,
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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5 CMU200 instruments also support AMPS, IS-136, IS-95 (CDMA 2G) and both WCDMA
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Mychaela Falconia <falcon@freecalypso.org>
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6 and CDMA2000 varieties of 3G.
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Mychaela Falconia <falcon@freecalypso.org>
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7
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Mychaela Falconia <falcon@freecalypso.org>
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8 Over the course of owning and maintaining a CMU200 instrument since 2017 and
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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9 having had to repair it twice now (as of 2022-01), and having conversed with
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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10 another CMU200 owner who had to repair his instrument in the same way, I
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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11 started observing a pattern in that many of these instruments are now failing
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Mychaela Falconia <falcon@freecalypso.org>
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12 in the field in exactly the same ways. All of these failures happen in the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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13 RXTX board, and the purpose of this article is to educate other CMU instrument
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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14 owners about these failures and most importantly, how to repair them.
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15
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Mychaela Falconia <falcon@freecalypso.org>
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16 Credit attribution
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Mychaela Falconia <falcon@freecalypso.org>
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17 ==================
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Mychaela Falconia <falcon@freecalypso.org>
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18
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Mychaela Falconia <falcon@freecalypso.org>
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19 I sincerely thank Michael Katzmann, NV3Z / VK2BEA / G4NYV, for his invaluable
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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20 help in reverse-engineering the insides of the culprit RXTX board, identifying
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d2fef140ed53 CMU200-maintenance-notes: typo fix
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21 various critical components on that board, including the ones that habitually
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a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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22 fail, and identifying Eccosorb-caused galvanic corrosion as the root cause of
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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23 these failures. Without his help, I would not have made it this far!
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24
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Mychaela Falconia <falcon@freecalypso.org>
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25 What is this RXTX board
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Mychaela Falconia <falcon@freecalypso.org>
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26 =======================
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27
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Mychaela Falconia <falcon@freecalypso.org>
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28 This board is common among CMU200, CMU300 and CRTU-RU instruments from R&S - or
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Mychaela Falconia <falcon@freecalypso.org>
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29 at least these are the ones I know - maybe there are others I don't know about.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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30 This board encapsulates the instrument's main RF Rx and Tx chains: on the Rx
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7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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31 side it takes RF input from the front end and performs triple (or quadruple,
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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32 explained later in this article) IF downconversion to 10.7 MHz IF3, and on the
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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33 Tx side it takes 13.85 MHz IF3 input and upconverts it to RF output, going
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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34 through IF2 and IF1 in the process - triple or quadruple IF in both directions,
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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35 as explained in more detail later in this article.
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36
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Mychaela Falconia <falcon@freecalypso.org>
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37 Every CMU200 instrument always has one RXTX board - it is an absolutely required
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Mychaela Falconia <falcon@freecalypso.org>
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38 component irrespective of option configurations. The hardware architecture of
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Mychaela Falconia <falcon@freecalypso.org>
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39 this instrument also has a place for an optional second RXTX board, providing a
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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40 complete second Rx and Tx channel - however, as far as I can tell, CMU200
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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41 software won't do anything with it, i.e., there are no test modes or
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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42 applications in CMU200 software repertoire that can make use of a second RXTX
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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43 board. Instead it seems that configurations with two RXTX boards are better
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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44 supported on the CRTU-RU platform - but I know next to nothing about that one.
a87d9ee278fb CMU200-maintenance-notes: new article
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45
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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46 Also note: if your CMU200 is equipped with Aux Tx model B96 (as opposed to B95),
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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47 there is an output from that B96 add-on that goes to the front end input that
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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48 was originally meant for second RXTX.
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49
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50 RXTX board failures
a87d9ee278fb CMU200-maintenance-notes: new article
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51 ===================
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52
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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53 In terms of externally visible symptoms, almost all CMU200 units are now failing
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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54 in the same ways:
a87d9ee278fb CMU200-maintenance-notes: new article
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55
a87d9ee278fb CMU200-maintenance-notes: new article
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56 1) If Tx side fails, the visible symptom is completely absent or extremely weak
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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57 output, and the internal loopback test fails with no signal detected at any of
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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58 the frequencies in the test sequence. A key point is that this failure mode is
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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59 independent of the selected output frequency.
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60
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61 2) If Rx side fails, different frequency ranges are affected differently. As I
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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62 shall explain momentarily, there are two different IF1 Rx paths inside the RXTX
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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63 board: one handles the frequency range from > 1200 to <= 2200 MHz, and the other
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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64 handles lower (<= 1200 MHz) and higher (> 2200 MHz) input frequencies. When a
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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65 given RXTX board develops Rx path failure, this failure happens separately in
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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66 each of these two IF1 Rx paths. The resulting symptoms vary: if only one of
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Mychaela Falconia <falcon@freecalypso.org>
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67 the two IF1 Rx paths fails, then only that frequency range will be affected,
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Mychaela Falconia <falcon@freecalypso.org>
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68 or if both fail, the observed loss will typically be different between the two
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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69 frequency ranges. The failure symptom is unexpected large attenuation:
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Mychaela Falconia <falcon@freecalypso.org>
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70 sometimes around 5 to 6 dB of loss, othertimes as much as 25 dB of loss.
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71
85
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72 The internal loopback test invoked from the Maintenance menu is a good first
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73 step in diagnosis. In this test the instrument software configures both Rx and
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74 Tx chains to connect to RF1 (and then RF2 if you press Continue), and then it
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75 tests a longish list of different frequencies in sequence, spanning the full
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76 range from 10 to 2700 MHz. For each test frequency, the instrument software
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Mychaela Falconia <falcon@freecalypso.org>
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77 configures both the signal generator and the Rx chain, and it reports what was
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Mychaela Falconia <falcon@freecalypso.org>
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78 measured on Rx vs. what was put out on Tx. The test is considered a failure if
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79 nothing was received or if the Rx signal level was too far from the expected
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80 value, otherwise the test is declared as passed.
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81
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82 If the loopback test fails at every frequency with no signal detected, then you
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83 don't really know what's going on, and you will need to manually test Rx and Tx
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84 separately (using an external spectrum analyzer and an external signal
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85 generator) in order to figure out what is broken. However, out of the commonly
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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86 observed failure modes, dead Tx will produce this symptom.
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87
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88 If the Tx side is OK but Rx IF1 filters (one or both paths) have gone bad, the
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Mychaela Falconia <falcon@freecalypso.org>
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89 visible symptom in the loopback test will be Rx signal level that is lower than
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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90 it should be. The instrument software may declare the test as either passed or
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91 failed depending on the magnitude of the error: in this Mother's experience,
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parents: 84
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92 when one of the two IF1 paths on my CMU200 developed a loss of some 5.8 dB, the
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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93 loopback test was reported as passing - but a closer look at the numbers in the
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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94 report window showed the unexpected attenuation.
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95
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96 Because different input frequency ranges are handled via different Rx paths as
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parents: 84
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97 explained in the following section, when Rx IF1 filters fail, the loss behaviour
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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98 will be frequency-dependent. In the internal loopback test, you will see one
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parents: 84
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99 behaviour for frequencies from 10 to 1200 MHz, then a marked change for
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parents: 84
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100 frequencies from 1205 to 2200 MHz, and then another change (most likely a
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parents: 84
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101 reversion to low frequency behaviour) at the highest frequencies above 2200 MHz.
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parents: 84
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102
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103 We do not currently know if there are any other failure modes elsewhere in the
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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104 CMU200 instrument that can also cause a stepwise change in behaviour at these
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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105 frequency cutover points. It is my (Mother Mychaela's) suspicion that the front
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Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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106 end may have some filters too, each covering a wide frequency swath, with
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parents: 84
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107 instrument software switching these filters depending on the configured
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parents: 84
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108 listening frequency - but we don't know for certain if any such additional
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parents: 84
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109 filters are there or not. If you find yourself wondering whether the problem
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parents: 84
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110 you are seeing is in the RXTX board or the front end, the best way to narrow it
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parents: 84
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111 down would be to remove the semi-rigid coax pieces that carry RF between the two
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parents: 84
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112 and use an external spectrum analyser to look at the Tx output from the RXTX
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parents: 84
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113 board and/or the Rx output from the front end.
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114
83
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115 RXTX board architecture explained
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116 =================================
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117
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118 Unfortunately R&S' official service manual for CMU200 instruments is only a part
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parents:
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119 swapper guide: it tells you which boards do what in general terms and tells you
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120 how to remove and replace each part, but no schematics, and no detailed
85
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121 explanation of what happens inside each board. They do provide a little bit of
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122 info: I draw the reader to the block diagram on page 3.2 of this manual - this
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123 block diagram does provide an important starting point for understanding what
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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124 happens inside the RXTX board - however, it is simplified and incomplete.
83
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125
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126 In the Tx direction, 13.85 MHz IF3 comes in from the digital board - or from
a87d9ee278fb CMU200-maintenance-notes: new article
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127 B68 board in WCDMA test modes. This Tx IF3 is mixed with Tx LO3 to produce
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128 Tx IF2. This Tx IF2 is fixed at 487.52 MHz, thus one would think that Tx LO3
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129 frequency ought to be fixed as well - but it seems to be a synthesized variable
85
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130 frequency, and the manual describes it as "LO3TX with small tuning range".
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131 Calculations done by Michael VK2BEA put Tx LO3 at 473.67 MHz (needs
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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132 confirmation), but it is still not clear why it is a synthesized frequency
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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133 "with small tuning range", as opposed to simply fixed.
83
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134
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135 Tx IF2 of 487.52 MHz is then passed through a pair of identical SAW filters,
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
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136 Sawtek 855272 - two cascaded identical filters, with an amplifier in between.
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Mychaela Falconia <falcon@freecalypso.org>
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137 This SAW filter has a center frequency of 479.75 MHz with 20 MHz bandwidth,
a87d9ee278fb CMU200-maintenance-notes: new article
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138 thus the passband spans from 469.75 to 489.75 MHz. Notice how Tx IF2 of
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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139 487.52 MHz stands just 2.23 MHz away from the edge of the passband - is it
a87d9ee278fb CMU200-maintenance-notes: new article
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140 intentional? What are they filtering? Without original design notes, we can
a87d9ee278fb CMU200-maintenance-notes: new article
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141 only guess. As I shall explain later in this article, one of these two Tx IF2
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parents:
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142 SAW filters is a component prone to failure.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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143
85
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144 [Note from Michael VK2BEA: "The LO frequency is only 13.85 MHz from the IF. It
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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145 makes sense to shift this to the edge of the passband to help the suppression
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146 of LO feed through. Also explains the use of SAW filters (sharp skirts) and
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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147 that there are two."]
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148
83
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149 After these cascaded SAW filters, Tx IF2 is mixed with LO2. Unlike LO1 and LO3,
a87d9ee278fb CMU200-maintenance-notes: new article
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150 there is only one LO2 for both Rx and Tx, and it is fixed at 1329.6 MHz. When
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
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151 Tx IF2 at fixed 487.52 MHz is mixed with LO2 at fixed 1329.6 MHz, the output of
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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152 this mixer will always contain two frequencies: 842.08 MHz and 1817.12 MHz.
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153 These are the two possible Tx IF1 frequencies, and there is a frequency-
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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154 selective filter for each of these two Tx IF1 modes. Based on the final output
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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155 frequency to be generated, instrument control software selects either low or
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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156 high Tx IF1, controlling switches before and/or after the filters. I have not
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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157 investigated to see if the frequency ranges for high vs. low Tx IF1 are the same
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
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158 as on the Rx side or not - maybe they are the same, maybe they are different.
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parents:
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159
a87d9ee278fb CMU200-maintenance-notes: new article
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160 After Tx IF1 output is combined or switched from the two filters, it is mixed
85
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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161 with Tx LO1 to produce an output that may or may not be final RF. The mixer
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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162 that does this job is MACOM SM4T, which is one of the larger, prominently
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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163 visible components on the board. Tx LO1 has "large tuning range and very fine
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
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164 frequency resolution used for setting the desired transmitter frequency" - quote
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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165 from the manual; by doing some frequency arithmetics, we can see that this Tx
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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166 LO1 tuning range needs to span from 1827.12 to 3042.08 MHz in order to produce
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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167 output frequencies from 10 to 2200 MHz starting from 842.08 MHz or 1817.12 MHz
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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168 IF1. (LO1 - IF1 is the desired output frequency, whereas the sum will be a
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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169 much higher frequency above 2.7 GHz - I presume that the latter must be
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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170 suppressed by some LPF somewhere.)
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171
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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172 The "RF" output from Tx SM4T mixer (LO1-IF1 as explained above) is indeed the
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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173 final RF output going to the front end for output frequencies below 2200 MHz.
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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174 In the uppermost frequency range of 2200 to 2700 MHz, a fourth mixer and LO
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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175 stage come into play - NOT shown on the block diagram in the manual! In this
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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176 highest frequency range, the output from SM4T mixer should be considered a
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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177 fourth IF - but because it is not covered at all in the manual and not named,
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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178 we have to invent our own name for it. I (Mother Mychaela) propose that we
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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179 call it IF0, and refer to the corresponding LO as LO0 - this way we remain
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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180 consistent with official naming that puts IF1 closest to RF and IF3 closest to
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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181 digital.
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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182
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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183 The preliminary analysis by Michael VK2BEA is that Tx LO0 frequency is fixed at
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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184 3318.46 MHz (same as its counterpart on the Rx side), with IF0 (taking the place
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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185 of lower RF) ranging from 1118.46 to 618.46 MHz (reverse range) to produce final
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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186 output frequencies of 2200 to 2700 MHz. However, these numbers have NOT been
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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187 confirmed by actual measurements yet.
83
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188
a87d9ee278fb CMU200-maintenance-notes: new article
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189 On the Rx side the same process happens in reverse, but the specific frequencies
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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190 used for IF1, IF2 and IF3 are slightly different. At first there is a stage
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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191 that only kicks in for frequencies above 2200 MHz (bypassed otherwise), and
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192 then there is an SM4T mixer (identical to the one on Tx side) that takes in RF
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
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193 and Rx LO1 to produce Rx IF1. High-side injection is used, i.e., Rx LO1 is
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
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194 programmed to generate frequency equal to the external RF of interest PLUS the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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195 desired Rx IF1 output.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
196
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
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197 Rx LO1 is programmed as follows by the instrument control software:
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
198
a87d9ee278fb CMU200-maintenance-notes: new article
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199 * Rx IF1 will be at 1816.115 MHz (call it high) if the listening frequency is
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
200 <= 1200 MHz or > 2200 MHz;
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
201
a87d9ee278fb CMU200-maintenance-notes: new article
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202 * Rx IF1 will be at 843.085 MHz (call it low) if the listening frequency is in
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
203 the intermediate range, i.e., 1200 MHz < RF <= 2200 MHz.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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204
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
205 In addition to programming Rx LO1 to produce the desired IF1 per the logic
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
206 above, the software also controls switches that select one or the other IF1
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
207 filter: either the filter that passes low IF1 or the one that passes high IF1.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
208
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
diff changeset
209 The filters used for low and high IF1 modes are the same on both Rx and Tx
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
210 sides. (The actual frequencies are slightly different, but in each case they
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
211 fit within the passband of the common filter parts.) The filter for low IF1 is
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
212 Murata DFC3R836P025HHD, package marking 836 CD, and the one for high IF1 is
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
213 DFC31R84P075HHA, package marking CR. The two filter packages are NOT the same
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
214 mechanically: the low IF1 filter is physically larger. Both parts are ceramic
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
215 monoblock filters from the same family, and it seems that these filter parts
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
216 were originally made for mobile phones, not for RF metrology instruments: the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
217 "836 CD" filter is for AMPS uplink band, and the "CR" filter is for DCS downlink
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
218 band.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
219
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
220 On the Tx side of the board there are only two IF1 filters: one for low Tx IF1
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
221 and one for high Tx IF1. However, on the Rx side there are 3 of these ceramic
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
222 filters in total: two for high IF1 (two cascaded identical filters with an
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
223 amplifier in between) and just one for low IF1. Why am I covering these filters
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
224 in so much detail? You probably guessed it: they are components that fail, as
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
225 will be covered shortly.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
226
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
227 After the selection of either low or high IF1 filter, Rx IF1 coming out of the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
228 selected filter (either 843.085 MHz or 1816.115 MHz) is mixed with LO2, which is
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
229 shared between Rx and Tx sides and fixed at 1329.6 MHz. The output of this
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
230 mixer is Rx IF2 at 486.515 MHz. This Rx IF2 then passes through a pair of
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
231 cascaded Sawtek 855272 filters, two identical filters with an amplifier in
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
232 between, exactly the same as on the Tx side. Then there is Rx LO3 and the final
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
233 mixer, producing Rx IF3 at 10.7 MHz that goes to the digital board, to the rear
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
234 panel BNC output and to the WCDMA board (B68) if the latter is present.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
235
85
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
236 Frequency conversion tables
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
237 ===========================
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238
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239 Michael VK2BEA worked out a pair of frequency conversion tables, one for Rx and
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
240 one for Tx. Here are these tables, with further corrections by Mother Mychaela:
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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241
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
242 Rx frequency conversion, RF to IF1:
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
243
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
244 RF (MHz) LO0 (MHz) IF0 (MHz) LO1 (MHz) IF1 (MHz)
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
245 ----------------------------------------------------------------------
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
246 10-1200 1826.115-3016.115 1816.115
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
247 1200-2200 2043.085-3043.085 843.085
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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parents: 84
diff changeset
248 2200-2700 3318.46 1118.46-618.46 2934.575-2434.575 1816.115
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
249
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
250 Rx frequency conversion, IF1 to IF3:
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
251
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
252 IF1 (MHz) LO2 (MHz) IF2 (MHz) LO3 (MHz) IF3 (MHz)
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
253 --------------------------------------------------------
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
254 1816.115 1329.6 486.515 497.215 10.7
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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parents: 84
diff changeset
255 843.085 1329.6 486.515 497.215 10.7
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
256
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
257 Tx frequency conversion, IF3 to IF1:
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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258
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
259 IF3 (MHz) LO3 (MHz) IF2 (MHz) LO2 (MHz) IF1 (MHz)
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
260 ---------------------------------------------------------
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
261 13.85 473.67 487.52 1329.6 1817.12
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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parents: 84
diff changeset
262 13.85 473.67 487.52 1329.6 842.08
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
263
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
264 Tx frequency conversion, IF1 to RF:
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
265
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
266 IF1 (MHz) LO1 (MHz) IF0 (MHz) LO0 (MHz) RF(MHz)
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
267 ------------------------------------------------------------------
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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parents: 84
diff changeset
268 1817.12 1827.12-3017.12 10-1200
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
269 842.08 2042.08-3042.08 1200-2200
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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parents: 84
diff changeset
270 1817.12 2935.58-2435.58 1118.46-618.46 3318.46 2200-2700
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
271
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
272 Notes:
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
273
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
274 * In Michael's original version each table covered the full chain from RF on
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
275 one end to IF3 on the other end, but I (Mychaela) had to split each table
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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parents: 84
diff changeset
276 into two in order to fit within 80 columns.
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
277
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
278 * The numbers for LO3 (473.67 MHz for Tx, 497.215 MHz for Rx) are from Michael;
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
279 I (Mychaela) have not verified them.
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
280
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
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diff changeset
281 * All details for the IF0/LO0 stage (upper frequency range) are from Michael;
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
282 his notes indicate that the numbers are confirmed for Rx, but not for Tx.
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
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diff changeset
283
83
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
diff changeset
284 How these RXTX boards fail
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
285 ==========================
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
286
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
287 There are 3 specific components on this RXTX board that have been seen to fail
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
288 over and over in the field:
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
289
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
diff changeset
290 * The second of the two cascaded IF2 SAW filters (Sawtek 855272) on the Tx side
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
291 often fails, breaking the Tx chain (output totally gone or extremely weak)
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
292 for all frequencies. Note that there are a total of 4 identical Sawtek 855272
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
293 filters on this board (2 on Rx side, 2 on Tx side), and only one of the four
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
294 fails: Tx side, second filter in the cascade.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
295
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
296 * The "836 CD" filter on the Rx side is prone to failure. When it fails, the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
297 visible symptom is severe attenuation in measured Rx signal levels for input
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
298 frequencies in the 1200 MHz < RF <= 2200 MHz range. Only the Rx side filter
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
299 fails, not the identical one on the Tx side!
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
300
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
diff changeset
301 * One of the two cascaded "CR" filters on the Rx side likewise fails - this time
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
302 it is the first one in the cascade. The other two identical "CR" filters on
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
303 the same board (the second in cascade for Rx and the one for Tx) are likewise
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
304 NOT seen to fail.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
305
a87d9ee278fb CMU200-maintenance-notes: new article
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parents:
diff changeset
306 The root cause of all 3 component failures has been traced to galvanic corrosion
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
307 caused by direct contact between these components and Eccosorb RF absorber foam.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
308 The complete RXTX board assembly consists of the traditional PCBA plus heavy
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
309 metal shields on both sides; the front and back metal shield pieces are custom-
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
310 made for this board, with individually shielded cavities matching different
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
311 sections of the board. Some (not all) of these cavities are filled with a
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
312 special black foam called Eccosorb - it is an RF absorber, presumably added to
85
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
313 lower the Q of these cavities to prevent parasitic oscillations. Trouble occurs
83
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
314 when this Eccosorb foam comes into direct contact with metal surfaces of
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
315 components on the board: the result is galvanic corrosion, a process that takes
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
316 many years before it results in component failure. The reason why only 3
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
317 particular filter components fail is because they got the bad luck of residing
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
318 in cavities with Eccosorb - the other identical components that don't fail
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
319 reside in cavities without Eccosorb.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
320
85
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
321 [Note from Michael VK2BEA: "The copper surface of these filters form an integral
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
322 part of the component. It is this copper that forms the cavity of the combline
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
323 filter. When this is compromised by corrosion, the filter is detuned and there
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
324 is leakage causing excessive loss."]
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
325
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
326 It appears that R&S only noticed this design flaw toward the end of "product
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
327 life" of these instruments, probably because failures occur only after many
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
328 years. Some of the newer boards have had modifications to prevent contact
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
329 between Eccosorb and the two troubled Rx filters, either by way of thinner
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
330 Eccosorb fill or by way of an added plastic barrier. It is not clear if these
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
331 modifications were applied to newer produced RXTX boards from the start, or if
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
332 they are a result of field service repairs.
83
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
333
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
334 How to repair failed boards
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
335 ===========================
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
336
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
337 All 3 of the failing filter components (one SAW filter part and two ceramic
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
338 monoblock filter parts) are now unobtainium. However, because so many of these
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
339 RXTX boards fail in exactly the same ways, our community at large is now
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
340 accumulating a very substantial "graveyard" of failed boards, and here is the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
341 good news: we can make one good board out of every two failed ones. Suppose
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
342 that every RXTX board in our community's collective inventory has fully failed,
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
343 leaving no failure-free boards - what now? Here is the recipe for making one
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
344 good RXTX board out of two fully failed ones:
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
345
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
346 1) Out of the two failed boards, choose one to be the part donor and the other
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
347 to be the part recipient.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
348
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
349 2) Take the part donor board and harvest 3 parts from it: one of the 3 Sawtek
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
350 855272 filters that aren't subject to corrosion, and the two IF1 filters
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
351 (one 836 CD and one CR) from the Tx side. Tx side IF1 filters aren't in
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
352 contact with Eccosorb and thus don't corrode, and 3 out of the 4 SAW filters
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
353 are likewise safe - hence we expect that every "dead" RXTX board can still
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
354 serve as a donor of good parts in this manner.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
355
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
356 3) Take the part recipient board and transplant the donor parts onto it,
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
357 replacing all 3 corroded filters.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
358
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
359 4) Before putting the repaired board back into its metal casing, cover all
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
360 corrosion-prone components with Kapton tape, preventing direct galvanic
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
361 contact with Eccosorb - this way the newly transplanted uncorroded components
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
362 won't suffer the same fate.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
363
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
364 RXTX disassembly instructions
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
365 =============================
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
366
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
367 Before you can start working on an individual RXTX board, you first need to pull
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
368 it out of your CMU. Disassembly instructions are provided in the official part
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
369 swapper guide from R&S (which they call "service manual"), but here is the gist:
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
370
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
371 * Using a Torx T20 screwdriver, remove the 4 rear feet and lift the sleeve part
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
372 of the instrument case.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
373
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
374 * Remove two small Phillips screws that secure the cover over the main board
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
375 cage, and lift that cover off.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
376
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
377 * Unhook all MMCX little coax connections from the RXTX board: 3 on the top side
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
378 (IF3 interface) and one on the bottom (netclock input).
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
379
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
380 * Loosen and remove the two semi-rigid coax pieces that connect RF between the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
381 RXTX board and the front end. In this Mother's opinion, this step is the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
382 least pleasant of all, but it is unavoidable.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
383
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
384 * After ensuring that nothing remains connected to the RXTX board on the bottom
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
385 side, pull the board out from the top.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
386
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
387 Once you got the complete RXTX board assembly out, how do you extract the actual
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
388 board out of the metal casing? The not-immediately-obvious answer is that you
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
389 don't need to remove all of the screws, instead there are shortcuts that will
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
390 save you a lot of pain:
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
391
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
392 * There are two smooth thin metal plates, one on the front side of the board
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
393 (facing toward the front of the CMU when installed) and one on the back side.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
394 Each is secured with a small Phillips screw. You only need to remove the one
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
395 on the front side. You don't need to remove the thin metal plate from the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
396 back side of RXTX assembly - doing so will only add more clutter and loose
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
397 parts to your lab bench while the board is disassembled.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
398
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
399 * Once you remove the thin metal plate from the *front* side of your RXTX
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
400 assembly, you will see all of the many screws that hold together the sandwich
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
401 of two heavy metal pieces with the board in the middle. These screws are
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
402 Torx T8.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
403
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
404 * Put the board down on your bench so that the side that faces the front of the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
405 CMU when installed (the side with the T8 screw heads) will become the top,
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
406 with the rear side becoming bottom.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
407
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
408 * Each of the T8 screws passes through thread in the top metal piece, a hole in
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
409 the PCB, and then thread in the bottom metal piece. As you loosen these
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
410 screws, you don't need to remove them all the way - instead loosen each screw
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
411 so that its far end comes out of the thread in the bottom metal piece, but
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
412 let it remain captive in the top metal piece. Letting the screws remain
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
413 captive in the top metal piece will reduce bench clutter while the board is
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
414 disassembled, and there is a lot less screwing and unscrewing work to be done,
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
415 as there is no need to work through the thread in the top metal piece.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
416
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
417 Once you loosen all of the T8 screws, the top metal piece should lift off,
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
418 leaving just the bottom metal piece and the PCBA. The bottom metal piece has
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
419 two thin metal pins sticking out of it; both the PCBA and the top metal piece
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
420 align on these two pins.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
421
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
422 When you lift the top metal piece (the one with the screws), the side of the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
423 board that will be immediately exposed to you is the side that faces the front
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
424 of the CMU when the board is installed. It is the Rx side, and you can confirm
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
425 that you are looking at the Rx side by noting that there are two "CR" filters
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
426 for high IF1, as opposed to just one. And chances are, right here at this step
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
427 in the disassembly process you will see the galvanic corrosion or the lead-up
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
428 to it.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
429
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
430 As you lift the top metal piece from the board, look at its inside and note the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
431 many individual cavities. Also note how some of these cavities are filled with
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
432 some black foam - that's the Eccosorb. And note how only some of the cavities
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
433 have Eccosorb in them, not all.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
434
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
435 Now look at the ceramic IF1 filters on the Rx side of the board. The one "CR"
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
436 filter that is NOT in contact with Eccosorb will be bright copper-colored (it
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
437 actually is copper), whereas the two filters that are in contact with Eccosorb
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
438 (one 836 CD, one CR) will often be green instead of copper-colored on their top
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
439 surface - that's patinated copper! Furthermore, there will typically be some
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
440 black Eccosorb material directly adhered to the corroding top surfaces of those
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
441 two unlucky filters.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
442
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
443 Now lift the PCBA off the two metal pins, separating it from the bottom metal
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
444 piece. Like you did with the top metal piece, observe the inside of the bottom
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
445 metal piece: note which cavities have Eccosorb in them and which don't. Then
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
446 flip the board over and look at its Tx side. You will see that there are only
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
447 two ceramic IF1 filters on this side (one 836 CD and one CR), and both should
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
448 be in pristine shape, bright copper-colored, no corrosion - these two are not
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
449 in contact with Eccosorb!
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
450
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
451 Now look at the two Sawtek 855272 filters on the Tx side. The one closer to
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
452 the middle of the board will often appear in worse physical condition that the
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
453 other 3 - and the culprit is once again in contact with Eccosorb.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
454
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
455 MACOM SM4T mixer corrosion
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
456 ==========================
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
457
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
458 Neither I nor my collaborator on this project have seen an RXTX board on which
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
459 either the Rx SM4T mixer or the Tx one went bad - i.e., we haven't seen a
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
460 failure in this part *yet*. However, this mixer *is* in contact with Eccosorb,
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
461 and looking visually at the collection of RXTX boards in my possession, I
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
462 (Mother Mychaela) see definite signs of corrosion - the metal surface of this
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
463 SM4T mixer component is beginning to corrode. Therefore, as a preventative
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
464 measure, I recommend cleaning off any Eccosorb that is adhered to this component
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
465 and then covering the component with Kapton tape before putting the board back
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
466 into its metal casing.
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
467
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
468 Unlike the failing filters, this MACOM SM4T mixer is still available new - but
a87d9ee278fb CMU200-maintenance-notes: new article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
469 it's an expensive component, so let's protect these mixers from corrosion.
85
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
470
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
471 [Michael VK2BEA notes: "The case of the mixer is purely for shielding and is
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
472 much thicker than the thin copper of the filter that is essential for
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
473 operation." Mother Mychaela's response: it may be so, but if you are going to
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
474 take the RXTX board out of your CMU, take it out of its metal casing and either
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
475 replace filters or at least cover them with Kapton tape for protection, it
91
2ac06a49dfbc CMU200-maintenance-notes: typo fix
Mychaela Falconia <falcon@freecalypso.org>
parents: 85
diff changeset
476 won't hurt to put the same Kapton tape on the mixers too - and the signs of
85
7fc66c5b54dd CMU200-maintenance-notes: updates from Michael VK2BEA
Mychaela Falconia <falcon@freecalypso.org>
parents: 84
diff changeset
477 corrosion are very real.]