[amsat-bb] Re: Automatic doppler tracking of DSB

[John B. Stephensen]

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 at cox.net>
To: <amsat-bb at 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
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