[amsat-bb] Thoughts on ISS packet switch back to 145.825 MHz (long)

Stefan Wagener wageners at gmail.com
Sun Apr 16 23:25:24 UTC 2017

Thanks Kevin,

I appreciate your insight and experience. Thanks for your work as a
statewide packet coordinator. That is great!

I just worked the last ISS pass 20 min ago and the ISS radio was silent for
20 sec+ in between most packets. NO, I do not believe that the cause is
colliding packets, since I can fire off rapid packets and they get repeated
quickly, if I choose to and NO, no one has ever told me that I create QRM
:-)  Traffic was low on the last pass. Made three contacts easily.

Hope that helps,


since you don't have a dog in this fight and you are not working ISS
packets, ther

On Sun, Apr 16, 2017 at 6:00 PM, Kevin M via AMSAT-BB <amsat-bb at amsat.org>

> > No, you are not creating QRM if the ISS does not repeat your packet.
> Listen to the path of the ISS and
> > you will hear that 50% of the time the radio is silent. It does not TX
> since there are no valid packets.
> > Where is the QRM?
> I don't have a dog in this fight since I don't work packet any more... but
> at one time I was a statewide packet coordinator and personally took care
> of numerous dual band packet nodes. I've listened to the audio while at
> those sites. There may be one thing to consider than a regular 'ground op'
> doesn't think of...
> At high altitude, the receiver can hear a LOT and there are a lot of
> packets that do not get decoded because two, three, even four or more
> stations will all transmit at once and cover some part of another stations
> packet, thereby negating each other. (FM capture effect does not really
> apply for packet unless it's near 100% with clear audio, which is rare.)
> Because those stations are not hearing each other, they will key up and
> transmit at will, whether another station is transmitting at the time or
> not. From the 'digipeaters' point of view, it hears only partial packets,
> with lots of overlapping signals, so it decodes none.
> Whether or not the activity is appropriate, I'm not commenting on that...
> but I'm addressing your question so that you can better decide for yourself
> that question. My answer to 'where is the QRM?' is... 'The radio is silent
> 50% of the time, because it cannot decode enough valid packets... true. But
> the reason it can't decode enough valid packets may well be (and most
> likely IS) that all the transmitting stations continually overlap each
> other. (QRM each other)' The error in the logic here is assuming that it
> doesn't retransmit because it doesn't 'hear'... On the contrary, it HEARS
> TOO MUCH and can't make sense of the mess to decode it. In other words, it
> manages to hear a packet in the clear, about 50% of the time.
> In simple terms, it's most likely silent BECAUSE of the QRM... as opposed
> to the silence being an indicator of a LACK of QRM as you have suggested.
> Which would be no different than SO-50 staying silent because 3-4 stations
> are all keying up at once and SO-50 can't make sense enough to decode
> someone's PL tone. In both cases... too many stations, bird can't hear...
> bird does not retransmit.
> 73 and good luck to all in finding a workable solution.  Kevin N4UFO
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