Next GSM class, RF Explorer and antennas

[Mychaela Falconia]

Hello GSM class,

This morning's videoconference session was a relative success: two
students joined me for the videoconf, and we covered a broad overview
of different topics involved in the venture of running your own GSM
network on a small-scale basis.

Our next class session will be held on 2024-Jan-06, which is also a
Saturday, same time as before: 18:00 UTC, which is also 10:00 USA
Pacific Standard Time.  In this next session we'll go deeper into the
topic of specific radio frequencies that are usable for GSM, how to
scan your local radio environment to see which GSM-usable frequencies
are available/unoccupied, and how to choose the frequency for your
hobbyist GSM cell in such a way that reduces as much as possible
the risk of you getting into legal trouble for it.

The recommended homework assignment before that next class session is
to acquire a handheld spectrum analyzer called RF Explorer 3G Combo.
Here are links to 3 different places where one can buy this device:

https://www.seeedstudio.com/RF-Explorer-3G-Combo-p-1266.html
https://www.digikey.com/en/products/detail/seeed-technology-co-ltd/109990009/5488212
https://www.amazon.com/Explorer-3G-Combo-Aluminium-Downloadable/dp/B018WKTPA0

Please note that the "3G" designation in the model name does not refer
to 3G as in cellular - instead it refers to this model supporting
frequencies up to approximately 3 GHz.  To be pedantic, the actual
upper limit for frequency on this model is 2.7 GHz, which is sufficient
for all GSM work: the highest frequency that exists in the world of GSM
is 1990 MHz, which is the upper limit of PCS downlink band.

In addition to the RF Explorer base unit sold at any of the links above,
you will also need an antenna that is suitable for receiving GSM
frequencies.  There is no such thing as a universal antenna that can
work at all frequencies; the two antennas that are included with the
unit are useful for other types of RF work (one is good for ham radio
bands, the other is good for 2.4 GHz WiFi work), but neither is
suitable for any of the 4 GSM bands.

For GSM-band antenna, here are a few choices that are available from
established online retailers:

https://www.sparkfun.com/products/8347
https://www.sparkfun.com/products/675
https://shop.sysmocom.de/Quad-band-omnidirectional-SMA-antenna-for-GSM/ant-sma-quad

The first of these links (SparkFun CEL-08347) is a very good antenna,
great reception, but its physical size (20 cm or 8" long) is rather
inconvenient when paired together with the very compact handheld RF
Explorer.  The other two antennas are smaller, but both are made in
right angle physical arrangement, which once again becomes inconvenient
with RF Explorer and similar instruments.  The antenna which I
personally like the best for these applications is SPK WTH43006 - it
is from the same family as the middle one from SparkFun (CEL-00675),
but straight instead of right angle.  Because neither SparkFun nor any
other retailer carries it (at least none that I could find), back in
2016 I bought a wholesale batch of them directly from the manufacturer.

A special offer for this class: if any of you, dear students, would
like to get a WTH43006 antenna (the one I prefer and recommend), you
can get one from me.  You will need to entrust me with your mailing or
shipping address (PO boxes are more than welcome, I use one myself),
and once you buy the RF Explorer main unit (I will need confirmation
that you actually bought it), I will send you one of my antennas free
of cost.  I can also include a couple of FCSIM1 cards (my own brand of
programmable SIM cards) that will become useful in a future class
covering SIM programming tools.

I now look forward to seeing you again in the next class on Jan 6, and
for those who did not attend this morning, you are still welcome to
join.  Today's class was just an overview, but with the next session
we'll be getting into more technical details.

Sincerely,
Mother Mychaela aka Mrs. Falconia

P.S. It is Mrs. Falconia and not Dr. Falconia because I am not a
doctorate holder - I worked my way to Principal Engineer level through
private industry, not through academia or university track.