[time-nuts] PLL behavior

[Azelio Boriani]

In my opinion you fall in the case of disciplining with holdover... this is
more like a disciplined oscillator (like a GPSDO) problem than a PLL.

On Wed, Sep 19, 2012 at 1:45 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 9/18/12 9:48 AM, Raj wrote:
>
>> If you break the DC control chain of the PLL with a A2D and a controller
>> and back with a D2A .. you would program the control with any kind of
>> behavior you want. Just a thought!
>>
>>  That is exactly what we do... the PLL is actually implemented digitally
> (DAC driving the VCO)..
>
> But what I'm looking for is a theoretical treatment of the output
> statistics (Allan Dev, mostly) in terms of the interrupted reference input.
>
> For context.. we do precision ranging of spacecraft in deep space by
> sending a hydrogen maser derived signal TO the spacecraft which locks a
> local VCXO to that signal, and then uses the VCXO to generate a return
> signal with a constant ratio (e.g. 880/741) to the input.
>
> By measuring the time it takes for the round trip (essentially counting
> phase cycles on the return signal (against our hydrogen maser, again), we
> measure Range and Doppler, which is then used to determine the position of
> the spacecraft.
>
> Typical performance is sub-meter and sub cm/sec.  (A very high performance
> would be that the transponder adds 4E-15 Allan Dev over 1000 sec... 1E-11
> or 1E-12 over 10-100 secs is more usual)
>
> What we want to know is "what happens if the receiver and transmitter
> can't run at the same time"?  Obviously, we have less information coming
> into the system (we see the uplink half the time, so right there, we have a
> 2:1 hit) and the ground end only sees the transmit signal half the time
> (another 2:1 hit), so, from an information theory standpoint we've already
> put ourselves in a hole, but, what does the statistics really look like for
> the turnaround loop..
>
> Full Duplex full power turnaround is expensive in power, mass, etc. (for
> instance, you have to have good filters to make sure that your receiver
> isn't corrupted by the transmitter)
>
>
>
>
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