[time-nuts] Speaking of Costas loops

Joseph Gwinn joegwinn at comcast.net
Fri Jul 5 20:39:02 UTC 2013


> Re: time-nuts Digest, Vol 108, Issue 28
> Message: 2
> Date: Fri, 05 Jul 2013 09:18:39 -0700
> From: Jim Lux <jimlux at earthlink.net>
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] Speaking of Costas loops
> Message-ID: <51D6F1DF.9090800 at earthlink.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> On 7/5/13 8:44 AM, Bob Stewart wrote:
>> Wouldn't a Cs or Rb clock in orbit be slow due to relativistic 
>> effects?  I'm pretty sure there is a relativistic correction to the 
>> GPS clocks.
>> 
>> Bob - AE6RV
>> 
>> 
> 
> I believe that the original WAAS repurposed transponders intended for 
> other L-band satellite signals (e.g. Sirius/XM/LightSquared).
> 
> As noted earlier in the discussion, the new satellites might have a 
> specialized payload, which could have a purpose specific coherent 
> transponder, rather than a linear translator.
> 
> If it is purpose specific and single channel, then making it immune to 
> the local oscillator is straightforward.

I worked on a proposal for the original WAAS system.  The WAAS signal 
is not a timing signal in the sense that GPS signals from space are 
timing signals.  WAAS instead sends out a stream of correction data 
that allows one to greatly improve the accuracy and reliability of GPS 
signals.  

So, unless things have changed greatly, the geostationary satellite 
that broadcasts the WAAS signal need not have an atomic clock.

Joe Gwinn



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