The FM PA can be more efficient than the linear PA. If you constrain the FM deviation to be very narrow you can get 6 dB greater power efficiency for FM given a fixed peak envelope power ("HF Radio Systems and Circuits," page 59).
73,
John KD6OZH
----- Original Message ----- From: "Robert Bruninga" [email protected] To: [email protected] Sent: Thursday, September 05, 2013 12:44 UTC Subject: [amsat-bb] A0 40 replacement (PSK31-Best of FM and Linear!)
As long as AMSAT-NA needs to concentrate on... Cubesats... I would really like to see the pursuit of linear transponders... on them instead of single-channel FM repeaters.
We can have the best of BOTH FM and Linear!
But we used to use a ucc1 in the navy to receive messages. http://www.virhistory.com/navy/rtty-mux-ucc1.htm It would allow us to receive something like 16 or 32 separate traffic
channels on one frequency.
We have that now in PSK31. Up to 30 channels in a single audio channel. So the ideal AMSAT transponder is a linear receiver (on 28.120 MHz) and an FM downlink of that single channel on UHF. This has the advantage of 30 individual linear uplinks to share amongst everyone, and the advantage of FM downlink so that everyone gets the same waterfall without added Doppler.
It's a win/win. And it is FULL duplex so that everyone can transmit simultaneously and everyone can receive everyone simultaneously. What more fun can that be!!!
See the design: http://aprs.org/psk31uplink2.html
And it all fits on a single 3.4" circuit board. Easy to fit in any Cubesat. Two such flight ready boards are ready by the Brno University in the CZECH Republic.
Bob, WB4APR _______________________________________________ Sent via [email protected]. 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