You are right -- I should have been more specific. My comments below refer to correcting for Doppler shift -- not for tuning the linear transponder.
Ron W5RKN From: Brian Lloyd Sent: Wednesday, August 04, 2010 5:45 PM To: Ronald G. Parsons Cc: greathoun...@aol.com ; flexradio@flex-radio.biz Subject: Re: [Flexradio] Another Satellite Question On Wed, Aug 4, 2010 at 5:12 PM, Ronald G. Parsons <w5...@w5rkn.com> wrote: Don't make the mistake that Icom did in their IC-910, etc. where if the 432MHz band is tuned up 5kHz, the 144MHz band is tuned down also 5kHz. The bands must tune in ratios of their frequencies, I.e., tune up 144MHz by 5kHz, the 432MHz must be tuned down by approximately 15kHz (use actual ratios of the frequencies). Are you sure? The birds have a linear translator. The relationship between frequency is fixed. So if the linear translator is inverting then increasing the uplink by 5kHz would cause the downlink to decrease by 5kHz. And then there is radial velocity correction, i.e. correcting both channels for doppler. In that case the correction IS a ratio of the frequencies. And that ratio depends on the radial velocity of the bird relative to your station and is constantly changing. The right solution is to calculate the radial velocity and do the doppler correction for both channels separately, so that the uplink signal stays fixed in the satellite transponder's passband. If you have software that does that you will see the frequency of both TX and RX changing by different amounts continuously. This is actually the correct thing to do. Oh and then there is the bozo on the other end who tries to correct *his* transmit frequency to keep his signal in the passband. :-) It don't come easy! -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.931.492.6776 (USA) (+1.931.4.WB6RQN) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
