RadioBanter - View Single Post

November 4th 05, 03:24 PM

wrote:
Well actually, the project I had in mind was to take the 60 khz WWVB
signal and use diode harmonic multipliers to create a clock in the
gigahertz range. I would then use this clock as the input to a DDS
system. I could use the GPS to calculate lightspeed delay between
the VFO and the WWVB to determine compensating phase lag.

This could be good for synchronizing the transmit and receive ends of a
digital communication, improving the signal to noise ratio.

Wow... multiplying a very noisy 60kHz WWVB signal up to the gigahertz
using diode multipliers. Astonishing. Unless you live in the shadow
of Boulder CO, WWVB will be so noisy that after multiplication
you just have a huge broad hash of frequencies. It's buried in the
hash of noise most of the time anyway. And here on the East
Coast, WWVB reception is only barely usable for a few hours in the very
early AM (and not even that if there's a broadband LF noise source
anywhere in the vicinity.)

Receiving WWV (2.5, 5, 10, 15, and 20MHz) or WWVH is not quite so
problematic (usually in the continental US one of those frequencies
is receivable) but still not easy. And in say Asia or Europe or
South America most of those frequencies will not be open most of the
time, and there are local time/freq stations on those same frequencies
often. But multiplying what is usually a noisy carrier up to the
GHz via diode multipliers is still completely unthinkable.

What *is* done is to lock a high-stability OCXO to a time/freq
standard. This is often used for extremely-narrow-bandwidth moonbounce
communications for example. In the past decade almost all of this
is done by locking to GPS satellites, but if WWV or WWVB is receivable
at both ends this has been done too.

You do have the right spirit (low-bandwidth-for-low-noise requires
an accurate frequency standard) but multiplying WWVB into the GHz
using diode multipliers is decidedly *not* the way to do it. OCXO's
are cheap and GPS receivers are cheap and GPS is receivable everywhere
around the world and PLL's are so easy to do, so that's what
we use now. Before that PLLing a crystal oscillator to WWV/WWVB (
even if the PLL was a guy's ear listening for zero-beat and a
screwdriver
to tweak the oscillator fine-tuning) was
reasonable but there you're up against propogation and varying
path-length much of the time.