[time-nuts] Speaking of Costas loops

[Magnus Danielson]

On 07/05/2013 10:39 PM, Joseph Gwinn wrote:
>> 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.

This is naturally still true, but we are into the level of "there's a 
signal here, what can we use it for?". Doing a much simplified receiver 
could serve some well enough, without going the full mounty. It's like 
taking the color-carrier of analog TV broadcasts.

Cheers,
Magnus