[amsat-bb] PSAT PSK31 experimental software

[Graham Shirville]

And for OSCAR NEWS :)

73

Graham
G3VZV

-----Original Message----- 
From: EMike McCardel
Sent: Thursday, July 16, 2015 3:45 PM
To: aflowers at frontiernet.net
Cc: amsat-bb at amsat.org
Subject: Re: [amsat-bb] PSAT PSK31 experimental software

This could make for a great AMSAT Journal article!

EMike

EMike McCardel, KC8YLD
VP for Educational Relations AMSAT-NA

Sent from my iPhone

> On Jul 16, 2015, at 8:28 AM, "aflowers at frontiernet.net" 
> <aflowers at frontiernet.net> wrote:
>
> Bob, Dave;
> 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:
>
> http://www.urel.feec.vutbr.cz/esl/files/Projects/PSAT/P%20sat%20transponder%20WEB%20spec02.htm
>
> 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.
>
> Andy K0SM/2
>
>
>
>
> 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.
>
> THANKS.....
>
>
> BOB  KO6TZ
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> _______________________________________________
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_______________________________________________
Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
to all interested persons worldwide without requiring membership. Opinions 
expressed
are solely those of the author, and do not reflect the official views of 
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb