[time-nuts] Speaking of Costas loops

[Jim Lux]

On 7/3/13 2:21 PM, Dennis Ferguson wrote:
>
> On 3 Jul, 2013, at 11:47 , Bob Camp <lists at rtty.us> wrote:
>> The pipe in this case is up on one frequency and down on another. The conversion oscillator on satellite that's the weak link, no matter how good the signal from the ground happens to be.
>
> That's certainly true but it doesn't seem like a problem that the
> presence of a high stability free-running oscillator, like a rubidium,
> would help.  The oscillator on a geostationary satellite has a
> continuous frequency reference to lock to (the uplink carrier) and
> hence only needs short term stability sufficient to track this and
> transfer it accurately to the downlink.  It seems like this is the
> kind of problem that quartz excels at.
>

Kind of depends on what the transponder on the satellite looks like.

For deep space, we use a very narrow band loop filter to recover the 
received carrier.  The synthesis approach for the downlink is designed 
to cancel any variations in the local crystal oscillator (e.g. it's 
typically a ratio.. for X band, 880/749)