[amsat-bb] Re: Terrestrial QRM to FM satellites
Patrick STODDARD (WD9EWK/VA7EWK)
amsat-bb at wd9ewk.net
Thu Sep 20 09:45:41 PDT 2007
> Today on passes of both SO-50 and AO-27, there were
> terrestrial QSOs going on. It was especially bad on AO-27
> with a few people clearly unable to get through due to the
> strength of the QRM. It almost sounded like there was a
> repeater setup on 145.850 with Roger beeps happening.
> So, what is the "proper" thing to do in situations like this?
> Ignore it and talk to anyone who can overpower them?
> Stay off the air and hope you can hear callsigns that you can
> ask carefully to QSY?
> Something else?
AO-27 regularly picks up non-ham transmissions from Central America
(two-way radio and long-range cordless telephone conversations), and
lately I've heard what sounds like hams chatting on 145.850 MHz
simplex not realizing they are on a satellite uplink. Without the PL tone,
SO-50 won't retransmit the QRM, but the QRM sometimes overpowers
any legitimate transmissions up to the satellites. Up to now, it seems like
AO-51 has been free of the non-ham QRM.
In the past, the non-ham stuff from Mexico had been identified and - with
lots of pressure - the Mexican authorities forced the taxis and Red Cross
ambulances to move their radios to other frequencies. Unfortunately, some
of the new frequencies were somewhere else in the 2m band, but at least
the satellite uplinks were free from those QRM sources. It took a lot of work
by some Mexican hams to find the sources of the transmissions, sending
the documentation to the Mexican "FCC", along with complaints from
outside Mexico showing the international impact of these illegal
transmissions before any action was taken.
What should you do? If possible, record the passes that you work. You
never know what you might hear, and the recording might be useful for
someone trying to determine the source of the QRM. Generally, I just
try to work the satellite despite the QRM. With an HT, I might not get
through all the time, but I'll still try. If the QRM is from two hams chatting
on the satellite uplink simplex, they are not affected by your transmissions
up to the satellite unless they are close to your location. If it's
America or Mexico, the problem generally goes away on passes where
the satellites are moving from south to north - moving away from the QRM.
If you hear callsigns coming through the satellite from those chatting on 2m
simplex, and if you can find an e-mail address for those stations, send them
a note mentioning you heard them through a satellite and politely suggesting
they use another frequency. If you have a recording of the pass, send a
copy to them to show what you heard. Invite them to try working the satellite,
since they obviously have stations that are able to transmit to the satellite
based on what you heard.
Good luck and 73!
More information about the AMSAT-BB