Ideal AMSAT FM Transponder
The ideal AMSAT FM transponder for a cubesat is the PSK-31 transponder being developed for the Naval Academy PSAT mission.
With an FM downlink, anyone can receive it with an HT and a laptop with PSK-31 software. And anyone with a 10m PSK-31 uplink can transmit to it.
The reason it is ideal is that it is a multi-user transponder supporting up to 30 users at the same time. Everyone can transmit horizon-to-horizon and see everyone else. A big QSO party in the sky:
http://aprs.org/psat/PSK31-DESIGN-NOTES.html
And since it is FM, Everyone tuned into the downlink SEES THE SAME WATERFALL and sees EXACTLY where they are in the downlink. A small uplink doppler adjustment can keep each station locked to his chosen channel in the passband.
Everyone can talk to everyone if they want, or go one-on-one too.
The SSB uplink and UHF downlink transponder fits on a smaller than 3"x3" circuit board being developed by Mirek Kasal at Brno University.
If we could just get more Cubeats to fly these things, we would have all the joys of multi-user transponders, and yet they fit well in any cubesat. The ONLY problem is the HF wire antenna. Ours is going to be a 4 or 6' whip of Nitinol Wire.
In addition to thes PSK-31 transponder, PSAT also supports the usual APRS AX.25 transponder on 145.825 too. Launch is planned for Summer 2013.
Bob, WB4aPR
Hey Bob,
This might also be a great project for balloon launches as well, to be able to test all the ground station setups.
Any idea if these transponders will be made available to others after this project is completed ?
It appears that the Small Wonder Labs' PSK device is no longer available, pending a replacement that's in the works.
Take care,
Walter/K5WH
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Robert Bruninga Sent: Sunday, September 30, 2012 2:50 PM To: Amsat - BBs Subject: [amsat-bb] Ideal AMSAT FM Transponder
The ideal AMSAT FM transponder for a cubesat is the PSK-31 transponder being developed for the Naval Academy PSAT mission.
With an FM downlink, anyone can receive it with an HT and a laptop with PSK-31 software. And anyone with a 10m PSK-31 uplink can transmit to it.
The reason it is ideal is that it is a multi-user transponder supporting up to 30 users at the same time. Everyone can transmit horizon-to-horizon and see everyone else. A big QSO party in the sky:
http://aprs.org/psat/PSK31-DESIGN-NOTES.html
And since it is FM, Everyone tuned into the downlink SEES THE SAME WATERFALL and sees EXACTLY where they are in the downlink. A small uplink doppler adjustment can keep each station locked to his chosen channel in the passband.
Everyone can talk to everyone if they want, or go one-on-one too.
The SSB uplink and UHF downlink transponder fits on a smaller than 3"x3" circuit board being developed by Mirek Kasal at Brno University.
If we could just get more Cubeats to fly these things, we would have all the joys of multi-user transponders, and yet they fit well in any cubesat. The ONLY problem is the HF wire antenna. Ours is going to be a 4 or 6' whip of Nitinol Wire.
In addition to thes PSK-31 transponder, PSAT also supports the usual APRS AX.25 transponder on 145.825 too. Launch is planned for Summer 2013.
Bob, WB4aPR _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
At 05:49 AM 10/1/2012, Robert Bruninga wrote:
The ideal AMSAT FM transponder for a cubesat is the PSK-31 transponder being developed for the Naval Academy PSAT mission.
With an FM downlink, anyone can receive it with an HT and a laptop with PSK-31 software. And anyone with a 10m PSK-31 uplink can transmit to it.
This sounds like an interesting bird to try.
73 de VK3JED / VK3IRL http://vkradio.com
--- On Sun, 30/9/12, Robert Bruninga bruninga@usna.edu wrote:
With an FM downlink, anyone can receive it with an HT and a laptop with PSK-31 software. And anyone with a 10m PSK-31 uplink can transmit to it. The SSB uplink and UHF downlink transponder fits on a smaller than 3"x3" circuit board
Sounds great Bob.
I presume the reason for UHF downlink rather than 145 MHz, with it's lower Doppler shift, is due to other mission constraints ?
BTW is the uplink in the amateur satellite segment of 10m (29.3-29.5) or down at the bottom of the band ?
Hopefully IARU / ARRL will be successful in getting an Amateur-satellite allocation at 50 MHz since the CubeSat antenna problem would be easier to address on those frequencies.
A thought occurs to me. We use Oscar-7 mode B with its input outside the bands allocated to the Amateur-satellite Service. We can use it because various National Societies have negotiated with their Regulator to allow its use by amateurs in their country. I wonder if a similar approach would enable the use of 50 MHz as an uplink band prior to any WRC changes ?
73 Trevor M5AKA
I presume the reason for UHF downlink rather than 145 MHz, with it's lower Doppler shift, is due to other mission constraints ?
Yes, avoid QRM to the 145.825 APRS transponder.
BTW is the uplink in the amateur satellite segment of 10m (29.3-29.5) or down at the bottom of the band ?
Bottom segement. Think of it as a UHF linked band monitor for existing PSK31 operation on 10m usually between 28.120 and 28.123 MHz. The entire band is authorized by the ITU for satcom, though most band plans protect downlinks above 29.3 MHz.
This might also be a great project for balloon launches... to be able to test all the ground station setups. Any idea if these transponders will be made available to others after this project is completed ?
It will be up to Brno University and Mirek..
It appears that the Small Wonder Labs' PSK device is no longer available, pending a replacement that's in the works.
Yes, we used a Brno module for the first flight back in 2006 on PCSAT2 but then used a Small Wonder Labs PSK transceiver on the RAFT satellite in 2007.
The #1 hardest thing on making this system work, is getting the antenna tuned and resonant. This is a real challenge, because you cannot get inside the 4" cubesat with any instrumentation to tune for resonance. ANYTHING you connect to the spacecraft and antennas completely messes up the affect of the counterpoise.
The best method we have found is to just build the transponder, and then tweak a tuning element via a hole in the spacecraft until you can hear the best signal from the transponder listening to normal signals on 10m. Oh, and having the whole set up FAR away from the ground and ANYTHING else... It is a long and tedioius process.
We just did a preliminary EZNEC analysis, and the antenna impedance is something like Z = 2 - J1100 using a 6 foot wire.
Bob, WB4APR
participants (4)
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Robert Bruninga -
Tony Langdon -
Trevor . -
Walter Holmes