[time-nuts] Speaking of Costas loops

Bob Camp lists at rtty.us
Thu Jul 4 08:38:13 EDT 2013


Hi

The way doppler is corrected on a normal GPS is by having a large body of orbital data for each sat measured by a bunch of stations and then processed into the almanac. It's not a trivial process.

Since the doppler is in the hundred Hz or so range, I'd bet the conversion oscillator was designed to a similar spec. There may also be other issues as well. 

You would do *much* better for far less money simply using the same data collection process to do common view GPS with normal gear.

Bob

On Jul 4, 2013, at 3:06 AM, Hal Murray <hmurray at megapathdsl.net> wrote:

> 
> lists at rtty.us said:
>> If the WAAS sats were purpose designed to provide a high accuracy carrier,
>> then yes there are ways to do it. The fundamental design concept of a "bent
>> pipe" is that you don't do any of that. You do not care what's going through
>> the bird, it just maps the input frequencies to the output and amplifies
>> them (a lot). Again, the WAAS signal is simply piggybacking on existing
>> hardware. The conversion oscillator is not locked to the GPS carrier (or to
>> any other carrier). It's simply a free running quartz based oscillator,
>> running into a synthesizer to get the appropriate microwave frequency.  
> 
> If somebody wanted to use that path for a frequency reference, they could 
> setup a ground station to measure the Doppler and distribute that so people 
> could adjust their expectations.
> 
> I suspect measuring the Doppler is a common sanity check.
> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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