[amsat-bb] DopplerPSK - No 1 kHz-autotracking radio tuning

Thu Jun 13 17:54:26 UTC 2019

Everytime you step the radio frequency will cause a Phase shift and any
PSK31 decoding will loose sync until it can rephrase.  PSK31 needs phase
coherence well under 31 Hz to properly decode.

Better to tell your software to only step the radio once every 2.5 KHz maybe
to minimize these glitches and loss of characters while still keeping the FM
signal in the passband.

Bob, WB4APR

-----Original Message-----
From: Peter Goodhall (2M0SQL) <peter at magicbug.co.uk>
Sent: Thursday, June 13, 2019 10:22 AM
To: Robert Bruninga <bruninga at usna.edu>
Cc: AMSAT-BB <amsat-bb at amsat.org>
Subject: Re: [amsat-bb] DopplerPSK - No 1 kHz-autotracking radio tuning

Bob,

Yes they can correct too much smaller with CAT control, for NO-84 PSK I have
SatPC32 correct my IC-910 every 600Hz this doesn't appear to present any
problems and I've had many contacts.

Is there a reason why you're suggesting this isn't OK?

73,

Peter, 2M0SQL

On Thu, 13 Jun 2019 at 13:35, Robert Bruninga via AMSAT-BB
<amsat-bb at amsat.org> wrote:
>
> Question.  All FM-only rigs of course only do 5 KHz steps anyway.  Are
> we finding that multi-mode rigs when placed in FM mode can actually
> step smaller under CAT control?
>
> If so, then we must point that out to users, since it will not work
> for
> PSK31 even in FM.
>
> Thanks for the reminder.  If rigs do that, then I will add this to the
> PSAT web page.  The advice to not use auto-radio tuning except for 5
> KHz steps on the downlink.  IE, not smaller steps.
>
> Bob, WB4APR
>
> -----Original Message-----
> From: AMSAT-BB <amsat-bb-bounces at amsat.org> On Behalf Of aflowers---
> via AMSAT-BB
> Sent: Wednesday, June 12, 2019 10:58 PM
> To: amsat-bb at amsat.org; Scott <scott23192 at gmail.com>
> Subject: Re: [amsat-bb] DopplerPSK
>
>  Scott, Roy, Umesh, et al;
> Part of the problem with PSK31 is that it required the adjustment for
> changes in Doppler shift to be to be phase-continuous.  I think the
> Doppler rate (delta-Doppler shift) at even 10m is too fast for most
> radios--what you often get with CAT control, even if you can update
> while transmitting, is
> PSK31 that jumps more than 31Hz per update, and that totally destroys
> the phase continuity required to tell a '1' from '0'.  This was the "fun"
> problem that spurred me to take a swing at it over a summer vacation.
> When DopplerPSK applies "anti-doppler" on the transmitted signal, it
> does so at the baseband audio level.  This works fine for 3Khz
> passbands on a 10m uplink, but if you want to do it with SSB transponders
> and VHF and UHF
> you'll need an SDR where you aren't limited by an IF filter.   The same
> algorithm in DopplerPSK could be used on a complex signal in the SDR
> architecture, and it could work equally on TX and RX in the processing
> chain.   To the accuracy of the orbital elements everyone uses, if
> everyone
> corrects their uplink and downlink properly there is no perceived
> frequency drift by anyone using the satellite.  Just what you need for
> a GHz-range LEO with a narrow-band transponder, eh? Since the downlink
> of NO-84 is FM there is no Doppler shift in the baseband audio of the
> downlink--you hear what the satellite hears.  If we get a mode-K
> satellite it might be worthwhile to do a baseband demodulator in a
> soundcard since the total change in Doppler shift will be small enough
> to fit in a conventional HF radio's IF passband in both directions.
> If the antiquated hosting site doesn't come back I'll get off my duff
> and find a "proper" place for it.  It's nice to see people playing
> around with it. (Thanks for bridging the gap in the meantime, Peter.)
> Andy K0SM/2
>
>
>
>     On Wednesday, June 12, 2019, 9:24:12 PM EDT, Scott via AMSAT-BB
> <amsat-bb at amsat.org> wrote:
>
>  While it might certainly be possible to put together a solution that
> would compensate your uplink so that its corresponding downlink
> through the transponder holds stationary on a single spot on the
> downlink audio spectrum, there are two reasons (at least) that I can
> think of to not go to that trouble:
>
> #1, the DopplerPSK app takes care of it perfectly already.  The work
> has been done.
>
> #2, if memory serves, some radios do not respond to CAT frequency
> adjustments when transmitting.  In this mode, your uplink radio is
> transmitting non-stop for the entire ~10 minute pass.  If you have a
> hardware/software setup that can only change RF frequency when in
> receive mode, that will never happen during an NO-84 pass.
>
> Lastly, like much satellite work, the uplink and downlink are two
> completely separate discussions in this mode.  While the 10m uplink
> works extremely well with the DopplerPSK software and the HF radio of
> your choice, receiving & demodulating the PSK31 downlink can be done
> by any antenna/FM radio(or SDR), and computer combination of your
> liking.  Just as one example, my setup is:
>
> TX:  Windows PC > DopplerPSK > Signalink > FT-857d > MyAntennas
> EFHW-8010
>
> RX:  70cm X-Quad > SDRPlay RSP1 > HDSDR on Windows PC (doppler track
> w/
> Orbitron) > FLDigi
>
>
> -Scott,  K4KDR
>
> ==============================
>
> On Wed, Jun 12, 2019 at 8:20 PM k6vug at sbcglobal.net
> <k6vug at sbcglobal.net>
> wrote:
>
> > I'm very curious about this, thanks for sharing the links.
> >
> > Looks like the program adjusts the PSK modulation within the pass
> > band of the uplink, and at 10 meters, that would be relatively
> > small.  It makes sense, however would this work if SatPC32 manages the
> > uplink ?
> >
> > Secondly, I came across this on the website:
> >
> > "DopplerPSK does not provide any PSK31 demodulation; you should use
> > a separate program for that purpose. DopplerPSK does not provide any
> > compensation for downlink Doppler (which you would need for fully
> > linear transponders)."
> >
> > Question 2 - why not use something like HRD for everything (doppler,
> > psk, rotator, logging, etc) ?
> > (I believe I tried it sometime back by routing of the downlink audio
> > back into HRD)
> >
> > 73!
> > Umesh
> > k6vug
> >
> >
> >
> >
> >
> > On Wednesday, June 12, 2019, 8:10:11 AM PDT, Scott via AMSAT-BB <
> > amsat-bb at amsat.org> wrote:
> >
> >
> > I originally used the link on 2M0SQL's excellent how-to page:
> >
> > https://www.2m0sql.com/2018/10/29/using-the-no-84-psat-psk-transpond
> > er/
> >
> > ... which is:
> >
> > http://www.frontiernet.net/~aflowers/dopplerpsk/dopplerpsk.html
> >
> > If that link isn't available, you're welcome to the copy I
> > downloaded which has just been put at:
> >
> > https://www.qsl.net/k/k4kdr//downloads/DopplerPSK_0.2.zip
> >
> > -Scott,  K4KDR
> >
> > ==========================
> >
> > On Wed, Jun 12, 2019 at 10:53 AM Roy Dean via AMSAT-BB
> > <amsat-bb at amsat.org
> > >
> > wrote:
> >
> > > With all this talk of NO-84, and me finally having a
> > > semi-operational ground station - I went looking for DopplerPSK,
> > > but every link I found
> > was
> > > broken.  Where can I get this software?
> > >
> > > --Roy
> > > K3RLD
> >
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> official views of AMSAT-NA.
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