FM satellites
Posted: February 3, 2008 9:49 pmFiled under: amateur radio, space
Saturday I was trying to get an APRS beacon setup at MSFC to work thru the ISS digital repeater. I knew that with the upcoming joint Ops with Atlantis, the crew would have the ham gear shut down at least during the EVAs. I figured a beacon would get on the map, and stay on there, at least until the digi came back on. But I was too late already. The ISS crew did an EVA last Thursday, and afterwards the ARISS equipment was brought back up in FM repeater mode.
This is a cross-band mode that takes an FM input on 437.800, and retransmits on 145.800 whatever is on the uplink. Two tricky aspects to this being real useful.
- FM receivers favor the strongest signal
- 437 MHz band is subject to greater doppler shifting
So, if you can use a narrow-band, low-deviation, frequency agile transmitter, with more power than your neighbors, you can be heard. For those of us unaccustomed to using these orbiting FM repeaters, it is a challenge. I had to try it tho, and did manage a quick exchange with WF1F, Miles about 2215z on Sunday. Miles has some good advice posted on the AMSAT-bb email reflector about how to use this mode successfully.
On the heels of this slight success, I wanted to listen for AO-16. I share some history with this one, as I participated in the construction of this flock of four Microsats in the temporary AMSAT lab in Boulder Colorado in 1989. It was with this bird that I first enjoyed digital store and forward satellite messaging, and got started in telemetry processing. Oscar16 has just recently been rejuvenated and has returned to service as a FM satellite. This one has an interesting twist, as originally the output was a BPSK data stream, listening on the uplink for standard FM packet. So now it takes voice on 145.920 FM and returns double-sideband suppressed-carrier on 437.026… Still tricky tho, but I did manage one quick exchange with WD0EQP. Well, maybe I should try AO-51, as these were all lined up that afternoon… AO-51 takes input on 145.920 and return on 435.300… At least using a 2 meter uplink, you can focus on doppler correcting the receiver. Made another quick contact with AA2BN.
By this point I was feeling like I had been stuffed in a phone booth with half the hams on the east coast, trying to get a turn on one cellphone… I really wanted the taste of a good ol’ linear transponder, gimme some good ol’ SSB - and time to chat a few words, even sentences. ‘Back in the day’, ol’ AO-13 used to hang - way out there at apogee and we could go on for a long time. So along comes VO-52 in the schedule, and I’m thinkin, yeah - like Field Day !!! Got a passband, room for several at the same time… I somehow managed one contact, WB6YTE - as this is still a low earth orbit, and it went by pretty quickly.
Then I reminded myself that I only have a pair of Texas Eggbeater IIs in the attic - I was doing all this on indoor antennas ! And without the burden of trying to rotate the beams. I really need to get back with the program and get my tower re-planted, start growin some more antennas. I’ll leave you with this view of my AO-13 array, a pair of KLM-14c and a pair of KLM-18c …
Those were the days. 73 for now /;^)
February 10th, 2008 at 4:38 pm
Alan is my friend and satellite information expert, in fact the first time I ever visited him he was on Oscar 13 with his big array of antennas and fancy 736r rig, I wanted to do that satellite stuff……still do, I miss Oscar 13 and Oscar 10, they were fun birds…….
Thanks Alan for your continued encouragement and help, you always have a way of making me get the antennas out and tune on the satellite frequencies, still a thrill.
I might try hearing the S band downlink from ISS, I have my 706, 2304 looper, cable and transverter for 2304…..so while the Shuttle is docked maybe I can find the right freq.
We shall see………always something new to try, thanks to Alan.
Kind regards,
Mike Wechsler