[time-nuts] WWVB d-psk-r down conversion method

Charles Steinmetz csteinmetz at yandex.com
Tue Sep 23 14:23:51 EDT 2014

Paul wrote:

>This down converter system. Only detects phase change.
>    *   *   *
>Its output flips a signal path to invert or not invert the incoming wwvb
>signal that feeds the old radios.

Ahhh, you are just building a phase detector to trigger an 
inverter.  That's where I hadn't followed you.  As you note, the 
potential drawback of this approach is the length of time it takes to 
switch the inverter in or out after each phase shift:

>There is no need for an instantaneous response in the flip circuit. .3-.5
>seconds seems fine for the old radios. Want to see if I can get down to
>.1-.2 sec.

Depending on the stability of the disciplined oscillator (inside the 
old radio), you may need to do better than that.  If the old radio 
uses an OCXO and a very slow discipline loop, 100mS may be good 
enough.  But if it uses a TCXO or a naked crystal and the loop has to 
be fast enough to help stability in the 1S region, you may need to 
switch faster to avoid the PLL partially tracking the short burst of 
anti-phase.  Since analog PLLs are hard to make with long time 
constants (so the loops in the old radios are probably not as slow as 
you'd like), I suspect you'll see an improvement with faster 
switching.  Of course, you can run the 60kHz carrier through an 
all-pass filter before the phase switch to delay it if you need to, 
but you need to watch dispersion vs. temperature if you do that.

>Pretty sure from what I have seen so far there is no need to lock the LO
>nor must it be some precise offset of 100 Hz or anything else.

For that application, correct.

Best regards,


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