[time-nuts] Speaking of Costas loops
shalimr9 at gmail.com
Thu Jul 4 10:33:31 EDT 2013
That works well for transponders with o LY one signal. On commercial satellites, each transponder is shared among multiple signals, so that would not work.
Jim Lux <jimlux at earthlink.net> wrote:
>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
>> 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)
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