[amsat-bb] PSAT PSK31 experimental software

Thu Jul 16 19:57:49 UTC 2015

Andy

Here is a recording of the 1930 pass of NO-84
https://www.dropbox.com/s/2qtb5d2cm3ktrr0/FM%20435.359944MHz%20%5B12k%5D%207
-16-2015%2019%2033%2052.wav?dl=0 

Bob KO6TZ and I had a successful QSO. My audio was set at 1500 Uplink
frequency  of 28.119700 MHz .

The signals seemed to be stable, decoding at my end (DM780 ) was not
stellar, I'm running the recording through fldigi, MixW and Digipan to see
if it's any better.

Dave W0DHB

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of David W0DHB
Sent: Thursday, July 16, 2015 8:41 AM
To: 'aflowers at frontiernet.net'; amsat-bb at amsat.org
Subject: Re: [amsat-bb] PSAT PSK31 experimental software

Hey Andy

The ability to select soundcard would be helpful. In my setup TX audio is
fed by a virtual audio cable set to match the 48K sample rate that
DopplerPSK is using.
Folks using windows should set the recording device side of their soundcard
to a 48K sample rate (it usually defaults to 44.1K).

You are correct that the uplink frequency is high, I apply a -300 Hz
calibration offset.

Thanks for all your work on this.

Dave W0DHB

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of
aflowers at frontiernet.net
Sent: Thursday, July 16, 2015 6:29 AM
To: amsat-bb at amsat.org
Subject: Re: [amsat-bb] PSAT PSK31 experimental software

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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_______________________________________________
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