Arissat1 – First Attempt

a graphic of Arissat1I got up a bit early this morning and parked the car on top of the 6-story NIH garage in Bethesda to catch the 10:45 UTC (06:45 local) pass of Arissat-1. From there, the view North is unobstructed. The max elevation on this pass was 20 degrees, with AOS at azimuth 304 and LOS at 94, almost ten minutes in duration.

I tuned to 145.920 on USB and twirled the RIT back and forth above that frequency because I wasn’t sure how much doppler shift would matter. About a minute and half in, I picked up the CW beacon. I did not hear the bpsk signal as clearly as in this audio file. Here is what I heard this morning: Audio from Arissat-1 attempt #1 from FM19km.

In principal, to decode the BPSK1000 signal, the lower cw beacon should be kept near 500 hz. I tried my best, but after today’s experience, I realized I need something to look at — either some sort of spectrum display or the windows version of the TLM software. I had not played with the software earlier, but hoped that if I kept the signal within the receiver’s bandwidth, the decoding software would be pretty tolerant to centering, and might even track the signal pitch. Well, that is not the case. Maybe I can somehow pitch shift what I’ve captured, but I think the more practical solution is to try again, adjusting pitch live.

I did switch briefly to FM and heard just a couple syllables of speech before it went into SSTV mode and faded to static. In the above audio clip, the first part is USB, and you can easily pick out the CW signal. About halfway through, I switch to FM and you can definitely hear the SSTV, although the signal goes up and down rapidly (changing orientation of the satellite?).

I have to admit, this was something of a last minute effort, but I did remember to throw an audio splitter cable and the computer into the car before taking off to work today. I am not using a special antenna — just my trunk-mounted antenna (1/2 wave on 2m, 3 dBi). Considering that this was all before coffee, I guess I should consider myself lucky to have heard anything at all.

Later in the day, I fired up the Mac version of the TLM software, which seems less developed than the windows version. I tried to import a wave file, and it seemed to hang for quite a while, but them became responsive again. I assume it was trying to decode the bpsk, and having a hard time because the signal is very low in my recording and the frequency is all over the place. Unfortunately, for purposes of troubleshooting, no sample file is available on line, although the Arissat website says one will be posted shortly.

There’s another higher-elevation pass tomorrow at 11:23 Z / 07:23 local, and I’m planning to be set up for it. This time, I would use the PC-based version of the TLM software, which provides a real-time frequency analysis to keep the cw beacon in a narrow-enough window to center the bpsk1000 within the expected bandpass for decoding.

It would be helpful if I could figure out when the satellite is in eclipse, to know when it will be operating in lower power mode. I assume that it’s keps are not very stable, so I’ve just been going to the orbit prediction page.

Addendum: Not sure why the Amsat page just went down this evening (Aug 4th), but there’s another tracker that does a nice job — it shows whether the satellite is in eclipse or not, and if it is likely to be visible. It also provides real time tracking:

 

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