W2MMD Satellite Blog

The Russian crew on the ISS is broadcasting SSTV again.  Here's a screenshot of the W2MMD station receiving the downlink:

Lots of lessons learned...  The configuration was my i3-powered laptop running SDR Console and PST Rotator, the FT-991a and the large Arrow antenna. The first problem was that the uplink desensed the downlink, which meant that we couldn't find our downlink freq. Also - I generally find the downlink by speaking into the mic and finding that signal, but with so many other signals that wasn't possible. Finally I found that by switching to CW and pressing the MOX button on the 991a I could get a carrier that I could find in the downlink. But the desense continued until Jim Wright brought over his log periodic antenna and we used that for the downlink, separating the antennas by about 20 feet. That created enough separation to allow finding the downlink signal for the required 1 contact. Next year we need 2 different antennas separated as much as possible.  Other plans for next year: > Need headphones - too much conversation around the operating area > Need az-el rotation -

Finally had some success with PSK, and am starting to understand how it works. This was on Sunday of Field Day during which other stations may be working this satellite. Previously I only heard the W3ADO beacon, which occurs only about every 5 minutes. Now there were multiple stations on the waterfall. The transmitter desenses the downlink most of the time, although I finally got the audio setting so that I can hear our signal in the downlink (albeit with significant desense). The beacon usually appears around 500 hz, but out signal appears around 2.2 kHz, which would be set by the DopplerPSK program. I was running full power on 10 meters with the audio gain around 10:00 on the 847. Also note the other PSK signals that aren't being sent with DopplerPSK. Those are slanted because of the Doppler shift and can't be copied. Only sigs with DopplerPSK stay on freq and can be decoded. More on PSK from NO-84 K2za provided this link: https://www.2m0sql.com/2018/10/29/usin

Here's a link to the PowerPoint presentation at the GCARC Tech Saturday session in May 2018 on satellite operations. https://1drv.ms/p/s!ApbrAotXoVehn1X_NbnDl1UscOQQ

Last weekend Al KB2AYU and I (Al really did the work) put a Mirage 70 cm preamp up on the satellite antenna tree. Once installed we tested it and found that it made no difference in the received signal. So I had another identical preamp that I had tested and found working, so we swapped it out tonight - and found the same result. We had the control box that provides 12v to the preamp connected between the antenna switch and the antenna, and in that position it didn't work. So I decided to move it to the radio side of the switch and installed it with the control box input coming from the SDR radio and the antenna side of the box connected to the switch (the switch selects either the SDR radio or the 847 to be connected to the antenna). Strangely, this configuration worked! The noise level jumped about 20 db when the preamp was powered up, and a NO-84 PSK pass showed a much clearer signal on the downlink. Neither of us could explain why this configuration worked and the previous one

Testing today - use the SoundModem with the UISS program.  Launch SoundModem first since UISS will also launch the 1200 baud version of SoundModem, which you don't need and should close. But the HS version needs to be launched first to grab port 8000. Here are the SoundModem settings for FS3: Use COM5 for the PTT port for Rigblaster to key the 847 on 2 meters. Set the VIA call in UISS to PFS3-1.

The DopplerPSK program is used to correct a PSK signal for Doppler shift. It changes the audio frequency of the transmitted signal to do this compensation. The program download site is http://www.frontiernet.net/~aflowers/dopplerpsk/dopplerpsk.html  and it has been installed at C:\Users\user\Downloads\DopplerPSK_0.2.zip\DopplerPSK_0.2 on the W2MMD satellite computer.It uses Java, which has been installed (Version 8 Update 161 uninstalled, newer version installed ). Run the program from the shortcut on the Start menu. Looks like this:     Set the Audio Device on the menu to Rigblaster TX and set the Rigblaster TX switch to VOX (down position). This will key the 847.