[amsat-bb] PSAT PSK31 experimental software
aflowers at frontiernet.net
aflowers at frontiernet.net
Thu Jul 16 12:28:45 UTC 2015
That's great. I'm interested in how well it tracks when the satellite is at a very high elevation and the Doppler is >3 Hz/s. I suspect the error is going to be mostly in the estimates of the orbital elements, but we'll see. I will try to join you on the pass when I can cobble together an uplink and a downlink in the same place--probably next week sometime after I get back from vacation.
I think you should be able to share a sound device on most OS's, but I have not tried. I assumed it would work on modern Windows OS's because of the hardware abstraction. The program appears to run fine on OSX, but I have not tried running CocoaModem or some other software next to it. Ultimately I could also add a demodulator to the program itself, but that will take some work....I know several hams have separate sound cards for radio stuff, so I may need to add a device selection option in case the system default (or whatever Java picks as the default) isn't what you want.
The audio frequency displayed in DopplerPSK is the audio frequency being send to the radio, not what you should expect in the passband of your downlink receiver. The LO on PSAT is apparently a bit below 28120 KHz, so if your radio was tuned to 28120 USB (suppressed carrier frequency) you would expect to be a bit higher than 2000Hz in the FM passband:
In general, if you want to be lower in the passband I would lower your transmitter RF frequency rather than the audio frequency going to the transmitter. The reason being that if you have any non-linearity in the audio chain you don't end up transmitting a harmonic higher in the band that might bother someone else. Of course, you can probably see if this is an issue or not since the satellite also serves as a crude signal analyzer :-) I chose 2000 Hz as a center since at maximum Doppler of around 700 Hz, the ~2700 Hz tone should go through the transmitter's IF filter without too much attenuation while keeping all the third harmonics and most of the time the second harmonic above the cutoff of a 3 KHz IF filter. Every radio is a bit different, however. You may find that the 1500Hz sweep in the program shows you all your passband ripple in your IF filter :-)
Since it works, I'm more motivated to improve the ergonomics of the interface. Much of that depends on the unique operating practices of satellite operation.
On Thursday, July 16, 2015 12:31 AM, KO6TZ Bob <my.callsign at verizon.net> wrote:
The software worked great !!! Produced a straight line on the waterfall
for the down link.
As expected, I was alone on the pass, so no opportunity for a contact.
I was using digi-pan for the RX, my signal was at around 2200Hz..
Probably an indication the oscillator in my radio is off a bit. I think
I will lower the frequency from 2000 to about 1600. That will put my
signal lower in the VF pass band.
I like the program. Had good copy.
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