[amsat-bb] Help decoding/understanding terrestrial packet heard on ISS freq 145.825 MHz

John Brier johnbrier at gmail.com
Fri May 1 21:18:01 UTC 2015

Thanks for all the responses on SO-50 preamps and portable setups. I'm
still digesting the info.

TL;DR: I heard automated packet transmissions on the ISS packet
frequency when the ISS wasn't in sight and recorded them to try and
figure out who/what they are, but my software isn't decoding anything.
Can you help me understand what they were, or even better, decode them



Here's another question that has me excited:

Yesterday after having visited with family in Maplewood, New Jersey
for several days, I drove home to North Carolina. I knew there was an
ISS pass at 10:26 AM/1426 UTC, right when I started my trip, so I
tuned to 145.825 MHz and heard its digipeater easily.

Then I left the radio on.

I'm not sure where I was in NJ, but about one hour later, around 11:33
AM local/1533 UTC, I heard packet on the frequency again but I was
confused because there weren't supposed to be any more passes for a
while. I confirmed on my phone that the ISS was over some far away
ocean at the time I was hearing these new transmissions, so I knew
they must be terrestrial. Still, it seemed odd that someone or
something was transmitting when the ISS wasn't in sight...

Maybe it's an internet gateway I thought. Or do people leave their
stations on the ISS frequency 24/7 so they can "work" any pass that

I tried recording videos of the transmissions for later decoding to
figure out who or what it was. Eventually I realized it was
transmitting every 2 minutes. It was almost certainly an automated
setup, adding credence to the idea that this was an internet gateway.
Unfortunately, before I realized that, and after recording one video
of it, the best reception I received during my drive by "pass," I
wasn't recording. As I drove further away it only got weaker and
weaker. I did manage to get two half way decent recordings of it, but
I have tried decoding them with Soundmodem on Windows and it's not
printing out anything like it normally does. I am very new to packet,
only becoming interested in it because the ISS uses it, so I thought
maybe someone else might be more equipped to decode it. Or certainly
someone could shed some light on what I heard, maybe the operator in
NJ is on this list.

I used Audacity to record the audio off the videos I made as well trim
and amplify the audio, but I haven't done anything else, though if
someone wants the unedited videos I can put them up too.



John Brier, KG4AKV, Raleigh, NC, FM05

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