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)
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
