Tracking doppler on 2m and 70cm was hard enough at field day. I like 2GHz and up, but do not want to even think about the doppler.
In the KITSAT days, I used an IC-751 as the receive IF. It has a true FM detector, with discriminator centered at 0-volts. It steps in 1 or 10 Hz increments, even on FM. I wrote a simple radio-control program which would take data from InstantTrack, calculate frequency from that, and set the radio on the expected frequency at the beginning of the pass. Didn't matter if there was a little error, once AOS happened, the AFC put the receiver dead-on, and I got good data for the entire pass -- hands free. It was a joy to watch. And that was a simple digital mode.
The other thing that is exciting about going digital, is the idea of CAT-5 (or fiber) to the box at the antenna, not coax.
Digital will enable so much . . . .
73, Jim wb4gcs@amsat.org
On 7/27/2014 1:24 AM, Phil Karn wrote:
On 07/22/2014 07:49 AM, wa4hfn@comcast.net wrote:
SSB/CW birds are the only way to go and if you build it they will come .
Think about what it would be like to tune for Doppler while working SSB through a LEO satellite on microwave.
Before you say "computer control", work out the effect of even a tiny error in your clock or orbital elements on a high elevation pass and remember that SSB has no carrier or pilot tone for closed-loop frequency tracking.
Sure, you could have a second receiver track the satellite's beacon. But if you're going to all that trouble, why not just have it track a single high speed data stream from the satellite, one that's much less affected by Doppler in the first place? _______________________________________________ Sent via AMSAT-BB@amsat.org. 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
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