[time-nuts] Another "atomic" clock question
albertson.chris at gmail.com
Wed Mar 5 22:21:57 EST 2014
On Wed, Mar 5, 2014 at 5:43 PM, Didier Juges <shalimr9 at gmail.com> wrote:
> Tom and Bob,
> It is not obvious to me that it is "easier" to simply apply a correction in
> nS increments with a range as wide as 100nS. How is this done? Using
> switched delay lines or delay gates?
Here is my plan for processing saw tooth data. If it's not going to
work I'd rather hear about it now then a month from now after I've put
in some effort.
This is going into Lars' Arduino based GPSDO. Every second I read the
voltage on a TIC capacitor. This tells by the phase in nanoseconds
between the PPS and the OCXO. Then I add whatever the current GPS
sawtooth value is to whatever my TIC said. I compare this to a set
point. This is the phase error. The OCXO is adjusted based on a
filtered version of this error.
So in short, I don't correct even try to delay the pulse. I don't see
any need to do that. I measure the pulse and get a number in
nanoseconds. then I use sawtooth to correct the number.
It seems way-hard and with no purpose to correct the pulse and then
measure it. Better to correct the measurement. I think it is more
accurate too a delay could never be perfect.
The controller has LOT of spare capacity so I don't see way I can't
add one of more TIC channels and a few more DACs I should be able to
discipline an OCXO and my Rb oscillator from the same GPS PPS input.
The 74HC360 is only 1/2 used an Arduino has enough spare pins. Any
one more 74HC4046 and some passive parts would be required to build a
dual channel GPSDO.
It will be interesting to look at andompare the 10MHz outputs of two
oscillators that are being disciplined by the same controller and GPS
Redondo Beach, California
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