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