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!
Bob, WB4APR
-----Original Message----- From: Peter Martinez [mailto:[email protected]] Subject: Re: Receiving PSAT PSK31 FM downlink (Users Welcome)
Bob:
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.
73 Peter
----- Original Message ----- From: "Robert Bruninga" [email protected] To: "Miroslav Kasal" [email protected]; "Peter Martinez" [email protected]; "Urbanec Tomáš" [email protected]; "Petr Vagner" [email protected] Cc: [email protected] 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:[email protected]] Sent: Friday, May 22, 2015 11:51 AM To: [email protected] 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
WHAT TO DO:
- 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...
- 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).
- 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.
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 ... Duh!
Enjoy!
Bob, WB4APR