Perfect module (D751749ZHH)

[Mychaela Falconia]

Serg wrote:

> Seems like nice module, I see that it has at least 3 variants A/B/C, could
> not find a good document in English what is the difference.

It can be seen from Songbosi's huawei.jpg picture that the B version
is Calypso-based, whereas the C version is LoCosto-based.  Back in 2013
I made the decision to base my work on the Calypso chipset rather than
LoCosto, and this decision is now enshrined in the FreeCalypso project
name - and I am not switching.

If Serg or anyone else feels like playing with LoCosto, you are on
your own.

> Also seems like it has dual band SAW filters installed in B version, so
> additional components need to be installed in order to make it tri-band and
> following the re-calibration process executed.

Looking at Songbosi's huawei3.jpg picture (detailed view of the
component side of the board), it can be seen that the board CANNOT be
modified from dual-band to triband.  One can remove DCS band support
and add PCS band support in its place, but it is not possible to have
DCS and PCS on the same board without redesigning the PCB.  The antenna
switch only has two Rx paths coming out of it, not 3, and as you can
see in the photo, each goes through what looks like a series capacitor
acting as a high-pass filter.  The layout is done in such a way that
the series capacitor for the high band Rx path can be populated in one
way for DCS and in another way for PCS, but you still can't have both
at the same time with this PCB design.

To Songbosi: for my experimentation purposes I don't mind getting a
dual-band modem module without PCS band support: even though I am
located in USA-occupied California, I won't be operating the modem on
live airwaves here, instead I do all GSM RF testing on my CMU200
instrument, and with that instrument I can operate in any band in my
lab.  I would indeed be interested in getting a few of these modules
for experimentation and further reverse engineering, and Songbosi's
asking price is very cheap, but I would really need a breakout board
for the interface connector.

M~