AMSAT has only one full-time employee who is non-technical and the technical volunteers are usually working full-time elsewhere so responses can take some time. I've seen a description of the Costas loop in many engineering texts but have never seen it used for recovery of a suppressed carrier on a satellite downlink. There was some research on using pilot carriers for Doppler correction of SSB signals published in either QEX or the AMSAT Journal in the 1980's but it never caught on. I think that it was just easier to use the Keplerian elements to predict Doppler shift and do the correction open loop. The loop bandwidth for the Costas loop would also have to be fairly narrow so it may not work very well during the middle of a pass for LEO satellite.
73,
John KD6OZH
----- Original Message ----- From: "James Whitfield" n5gui@cox.net To: amsat-bb@amsat.org Sent: Friday, February 01, 2008 16:46 UTC Subject: [amsat-bb] Automatic doppler tracking of DSB
I am trying to find out if there has been any development of a frequency tracking system to compensate for doppler shift, or at least find a person or organization with which to discuss concepts. I tried to contact AMSAT about this more than a week ago, but there has been no response. I have tried to contact AMSAT again, and decided to try this bulletin board as well.
It started when I read that AO-16 had been placed in a test mode with an FM uplink and DSB downlink. I remembered a diagram of a double sideband suppressed carrier ( DSB ) demodulation technique that used a variation of a phased locked loop to recover the frequency and phase of the original carrier. I realized that it should be able to track the "original carrier" through the doppler shift caused by the relative motion between the satellite and the receiving station.
I decided to find out more about the concept. I was not able to find any reference to the technique having been used with satellites, but I believe the system is called a Costas Receiver, or perhaps is refered to as a Costas Loop.
If someone knows if this was used for doppler frequency tracking, please let me know where I can get more information. If there is a person or organization that would be better suited to my inquiry, I would like to know that as well.
Thank you.
James Whitfield n5gui _______________________________________________ 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