[amsat-bb] PSK-31 Author ideas

Robert Bruninga bruninga at usna.edu
Fri May 22 17:07:12 UTC 2015

PSK31 authors:

Peter Martinez G3PLX, original author of PSK31 reminds me that the ideal
Satellite PSK31 decoder would take advantage of the full-duplex links and
simply have the user click on his own signal in the downlink and then his
own softwar would AFC his uplink based on his downlink.  Thus everyone
remains locked in place in the waterfall!


-----Original Message-----
From: Peter Martinez [mailto:peter.martinez at btinternet.com]
Subject: Re: Receiving PSAT PSK31 FM downlink (Users Welcome)


In addition (or instead of?) urging PSK31 software authors to widen-out the
AFC on receive, it would be far better in the long term to get these authors
to include the ability to AFC the users uplink transmit frequency to null
the Doppler drift on the user's reception of his own signal in the downlink
baseband.   This will eliminate the risk of multiple uplink signals from
different directions drifting across each other, and opens up the
possibilities for many new techniques such as unattended reception (in the
same way that unattended reception of the tepemetry is possble now).

ModernPSK31 programs should have no difficulty letting the user spot his own
signal in the waterfall with a special mouse-click and applying the AFC to
the transmit audio tone while the program is running full duplex. The
multiple-receive features on these moderm programs can then be used to work
full duplex QSOs, with the user leaving his transmit signal keyed-on during
the whole pass.

Similarly, modern PSK31 programs should be able to measure the mean received
SNR of one's-own downlink signal and adjust the transmit tone amplitude to
keep the SNR to a reasonable level, say 14dB.  I have these two features
working on my own software today but this program is not sufficiently well
written that I am prepared to make it available on a wide distribution,
although program developers are welcome to have a copy to play with,
including the source code.


----- Original Message -----
From: "Robert Bruninga" <bruninga at usna.edu>
To: "Miroslav Kasal" <kasal at feec.vutbr.cz>; "Peter Martinez"
<peter.martinez at btinternet.com>; "Urbanec Tomáš" <urbanec at feec.vutbr.cz>;
"Petr Vagner" <petrv81 at gmail.com>
Cc: <bruninga at usna.edu>
Sent: Friday, May 22, 2015 3:55 PM
Subject: FW: Receiving PSAT PSK31 FM downlink (Users Welcome)

> PSK31 team.  How many of you are on AMSAT-BB?
> I am making many posts about PSAT there, and have very little time
> (Personal, work, and family crises)...  So can I assume you see all
> copies there?  If one of you is on AMSAT-BB, then you can forward to
> others anything about PSAT?  Here is the announcement.
> Bob
> -----Original Message-----
> From: Robert Bruninga [mailto:bruninga at usna.edu]
> Sent: Friday, May 22, 2015 11:51 AM
> To: amsat-bb at amsat.org
> Subject: RE: Receiving PSAT PSK31 FM downlink (Users Welcome)
> The Brno University builders of the PSK31 transponder on PSAT have now
> authorized user uplinks on 28.120 MHz PSK31 SSB.  Downlink FM on
> 435.350
> +/-
> 5 KHz doppler.   Here is the announcement from Brno University:
> "We can uplink open to all users. Please, do it." - Mirek OK2AQ
> Do NOT operate if PSAT telemetry is below 7.20 volts.  Cease operations.
> The voltage parameter is the second data field.  For example, this
> morning the telemetry packet is showing 8.99 volts in the second data
> field:
> T#658,899,072,583,875,854,00011100.  The third field is current (here
> showing 72 mA so Transponder is off.  When PSK is on, then current
> goes to over 300 mA)
> We'd like to get some packets in the DARK showing battery voltage
> while not charging?
> Enjoy
> Bob Bruninga, WB4APR
> -----Original Message-----
> Sent: Thursday, May 21, 2015 7:20 PM
> Subject: Receiving PSAT PSK31 FM downlink
> Receiving the PSAT (and BRICsat) 435.350 MHz FM downlink is as simple
> as placing  your PSK31 laptop microphone next to the speaker on your
> FM satellite UHF receiver and just watching the waterfall.
> What you see is exactly what everyone else sees (its FM).  There is no
> Doppler added to the tones due to your station's position relative to
> the satellite.  But you DO have to retune your FM radio at least 3
> times during the pass (+5 KHz, 0, -5 KHz) to stay in the FM passband.
> User uplinks, however, will shift in the waterfall according to each
> user's position relative to the satellite.  The shift can be as low as
> 1 Hz per second to as high as 6 Hz per second.  This is because the
> uplink is on 10 meters where the Doppler rate is only 1/15th of what
> it would be on UHF.
> The TELEMETRY channel at 315 Hz (PSAT) or 375 Hz (BRICsat) is FIXED
> with no Doppler since it is generated onboard into the FM downlink
> 1) We will need PSK31 authors to open the PSK31 frequency tracking to
> accommodate more than 1 Hz per second Doppler tracking.  Current
> implementations can do 1 Hz/s but completely fail at 3 Hz/s.  2 Hz/s
> might work a little...
> 2) Until then, ANY uplink user that is in line with a direct overhead
> pass will have minimum Doppler at the start and end of his pass (1
> Hz/sec) when the satellite is going right at him and directly away
> from him.  (Though it will be MAX (6Hz/sec) when it passes over his
> station).
> 3) Just turn on MULTI CHANNEL window and let the PSK31 decode everyone.
> The ones with the least Doppler at any instant may be decoded for a while!
> USERS can transmit later when BRNO University says it has completed
> its tests.  Brno provided the transponders for use in the PSAT and
> BRICsat satellites.
> So start preparing your station to TX PSK31 on 10 meters SSB and to
> receive the audio from an FM UHF rig on 435.350 +/- 5 KHz steps of
> Doppler.
> DOWNLINK Limitations:  The UHF downlink signal is only 300 mW and so a
> UHF beam is needed on the downlink.
> Dipole is authorized on the 10m uplink  and no more than 25 Watts (for
> now).
> Remember a 1/4 wave vertical is the ideal antenna because it maximizes
> the signal at lower angles and tapers the signal as the satellite gets
> closer.
> This keeps  user uplinks about the same during a pass.  Strong
> stations just drive down the AGC and ruin it for everyone.
> Use minimum power!!  Remember, this is crossband FULL DUPLEX so  you
> can see yourself in the downlink just like everyone else can see you.
> Act accordingly.  And of course DO NOT TRANSMIT if you cannot see the
> waterfall ... Duh!
> Enjoy!
> Bob, WB4APR

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