This message sent me on a Google search to find what I had missed about
WWVB. The terms I and Q signals sends me into phase modulation space. The
only reference I found on this is a 45 degree phase shift at 10 minutes
after the hour and a return 5 minutes later. Is there something else going
on with the phase of the WWVB carrier that I haven't heard about?
Regards.
Max. K 4 O D S.
Email: [email protected]
Transistor site http://www.funwithtransistors.net
Vacuum tube site: http://www.funwithtubes.net
Music site: http://www.maxsmusicplace.com
To subscribe to the fun with tubes group send an email to,
[email protected]
----- Original Message -----
From: "Kasper Pedersen" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Wednesday, April 22, 2009 1:25 AM
Subject: Re: [time-nuts] DSP WWVB Receiver Idea
Brooke Clarke wrote:
On the PICLIST there has been a discussion about the CMAX WWVB front ends
and noise. Olin mentioned that you could use a dsPIC to look at the I
and Q signals resulting from mixing the WWVB signal with a carrier at 60
kHz. His example case was to use a cheap crystal (+ or - 3 Hz) and so
use a 10 Hz low pass filter on the I and Q signals prior to squaring and
adding them.
I've built such a thing ( http://n1.taur.dk/dcf/ ). The zero-if I/Q
approach has a few things that make it less ideal than it sounds. There's
the 1/f noise, discovering and compensating for DC offset on each of the
channels requires that you remove the input, and it might not be a nice
divider from 10MHz.
If you choose a small arbitrary offset you can solve these problems in
software, only the filters in hardware need to be wider. Having the first
filters wide, I found, was a good thing: In the very early morning I get a
lot of sferics, and my steep filter rang like a bell with every crackle. A
low-Q front end allowed throwing those samples away.
Since that was done I have added a narrow bandwidth phase integrator
(2mHz) in software, and it will happily pull out ~10ns rms phase with a
+60dB carrier 1Hz from center. It even stayed locked when the antenna
amplifier broke and output 5Vp-p instead.
The real advantage of the I/Q method is that the bandpass filter becomes
two lowpass, and two lowpass is easier than a similar width bandpass with
enough precision and phase stability to be centered around 60kHz (and if
you use crystal resonators in the front end you can't track anything else,
and you get a problem with suppressing sferics).
You might not be able to get continuous reception no matter how hard you
try; I've seen inversions where the carrier just slowly fades and comes
back inverted with no apparent phase jumps (it looks like extremely slow
bpsk).
If I did it today I'd try phk's approach first. Preferably with a somewhat
tuned antenna to keep harmonics from PAL horizontal retrace from clipping
the converter. The one above was built with what was available in the
junkbox at the time.
/Kasper Pedersen
_______________________________________________
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.
_______________________________________________
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.
