[amsat-bb] Satellite SDR: Seeing IS NOT Hearing

[Clayton Coleman]

I happen to be a fan of using Software Defined Radio (SDR) to receive
amateur satellites. It is an inexpensive way to view all the signals
appearing on a satellite's passband simultaneously.  While I don't
normally run SDR full time at my station, from time to time I use it
to monitor activity on busy satellite passes because I can view and
record all activity.

As a result of more people using SDR on satellites, I have discovered
an operating trait that warrants some discussion and evaluation.

On more than one occasion, I have given a call to a very specific
station, and instead of my intended target had another SDR-based
station appear on frequency immediately saying "QRZ? QRZ?" rather than
wait and listen to who is calling on the frequency. The SDR user saw a
signal on their waterfall and clicked on it. They "pounced" on what
they perceived to be another station looking to make contact which
might not necessarily be the case.

I've see the same thing happen a few times with pileups.  There is an
existing pileup in progress when the SDR station comes into the
footprint. Rather than wait a short period to listen, they click on
the new signal in their waterfall, and immediately proceed to "QRZ" on
the frequency of the pileup, sometimes interrupting the flow of
existing contacts.

Just today I heard this scenario: Station 1 calls CQ.  Station 2 went
to answer. The SDR user clicked on the waterfall, heard only part of
the callsign of Station 2, and proceeded to call Station 2, ignoring
the possibility that Station 2 was attempting to QSO with someone
else.

It seems to me the visual nature of SDR waterfalls is causing a
temporary lapse in judgement when it comes to a basic ham radio
principle that we apply to satellite operating -- listen with our ears
before transmitting.

SDR is a great listening tool. With great power comes great responsibility.

73
Clayton
W5PFG