With your 2-radio setup, you should definitely leave your uplink frequency fixed, and tune only the downlink. Unless you have full computer control for doppler, this is the "One True Rule" anyway: tune only the higher of the two frequencies, where the doppler shift is greatest (about 9 kHz at 435). (If you ever get on VO-52, note that it has a VHF downlink and a UHF uplink, so you would tune the uplink there instead.)

Remember that the transponder is INVERTING: you must uplink on LSB, and listen to the downlink on USB. Also, the higher your downlink frequency is in the passband, the LOWER your uplink frequency will be. CW is generally found in the lower half of the passband (435.715 - 435.740) and voice in the upper half (435.740 - 435.765). Therefore, you should pick a downlink frequency above .740, and set your uplink radio to the corresponding frequency (the same amount DOWN from 145.950, the center of the uplink passband, as your downlink frequency is ABOVE 435.740, ie, an uplink of 145.940 for a downlink of 435.750) Pick a clear frequency, but don't go too high up, as most voice activity tends to stay pretty close to the center. For convenience, you might want to make up a little nomograph or chart that has the downlink frequencies on one line/column, and their corresponding uplink frequencies on another.

As far as power goes, the general rule has always been that your downlink should be no stronger than the beacon. That way, you're not tripping the AGC & knocking down someone else's signal. The FCC rule is, the minimum power necessary. Others have reported that 5 watts to an Arrow is sufficient.

Transmit either a slow voice count or a string of CW dits or V's while tuning your receiver around the predicted downlink frequency until you hear yourself. Early in a pass, while the bird is coming toward you, it'll be higher, and drift downward as the pass progresses. Call CQ, and listen for someone coming back. They probably won't be right on your downlink frequency, as doppler shift will be different at their location than at yours, so you'll have to tune your downlink to them. Hopefully, they will tune theirs to match yours. You'll get the hang of it pretty quickly.

Good luck, & hope to hear you on the birds!

George, KA3HSW

----- Original Message ----- From: "Mike Benonis" mailinglists@benonis.net To: "BB" amsat-bb@amsat.org Sent: Tuesday, December 29, 2009 1:41 PM Subject: [amsat-bb] HO-68 Linear Transponder - Newbie Questions

I'm a relative satellite newbie, and hence I don't have a base station set up. I do have a 2m SSB rig and an HT capable of SSB reception up at 435 MHz, as well as an Arrow antenna. With that in mind, does anyone have any tips for making contacts via the linear transponder on HO-68? Other than keeping my antenna pointed in the direction of the bird/rotated to avoid fades, how much do I need to compensate for doppler on the transmit and receive rigs? If I only tweak the RX rig, is that acceptable? Also, how much power should I use? Thanks for any advice this list might have!

73's de Mike KI4RIX

Best regards,

Mike Benonis mike@benonis.net KI4RIX