[amsat-bb] Receiving PSAT PSK31 FM downlink (Users Welcome)
wa4sca at gmail.com
Fri May 22 17:32:15 UTC 2015
This should get you started:
If the TX update step is greater than 1 Hz, go to the CAT tab. Select and store 1 Hz for the SSB/
CW interval. Check 10 X for the update speed. I have my usual 10 Hz selected, and a fast machine, so
I get 1 Hz steps without changing anything.
The downlink should be fine, but the uplink will probably require a bit of adjustment to match your
<From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Robert Bruninga
<Sent: Friday, May 22, 2015 10:51 AM
<To: amsat-bb at amsat.org
<Subject: Re: [amsat-bb] 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
<Bob Bruninga, WB4APR
<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
<WHAT TO DO:
<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
<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.
<UPLINK RESTRICTIONS: *NOTHING MORE THAN* a Vertical 1/4 wave or 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
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<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.
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