[time-nuts] GPS first LO need to be locked?

Magnus Danielson magnus at rubidium.dyndns.org
Fri Mar 31 15:04:41 EDT 2017


Hi,

On 03/30/2017 03:46 PM, paul swed wrote:
> I am curious if the first local oscillator on a GPS receiver must actually
> be locked or coherent to the reference oscillator in the GPS receiver
> typically running at some 10 MHz approximately. Or as long as the first LO
> is quite stable it doesn't matter because the receiver can track the code.
> This is a question for very classic receivers like Austrons, Odetics etc.
> Discreet. Modern fully integrated receivers are not in question.
> Thank you for your insights.

If you only do a code receiver, you can do this, but the carrier 
tracking will need to compensate the LO. This is naturally possible, but 
some of the precision will be lost. You can play some tricks to average 
this from the channels and sort things out.

If you want to do a carrier phase receiver, you would suffer too much, 
then you would need to lock the LO to get the gain.

For old receivers, I'd just assume the LO is locked, as it saves 
compensation tricks later, which would save computation cycles.
However, there where some crude receivers back in the days.

Cheers,
Magnus



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