On Wed, 30 Nov 2016 00:04:30 -0500, Michael Black
wrote:

On Tue, 29 Nov 2016, Jeff Liebermann wrote:

On Tue, 29 Nov 2016 22:48:31 +0100, "Carlos E.R."
wrote:

My clocks (I have 4) do not have a ferrite rod, like those in the
wikipedia. Unless minimal and well hidden.

They have ferrite rods buried inside somewhere. Even the "atomic
wris****ch" has a tiny loopstick coil inside. Look for something like
these, which are a bit large for a wrist watch:
http://www.c-max.com.hk/en/technology/rct/rct_perp
http://www.c-max-time.com/products/showProduct.php?id=20
The key performance factor of a VLF receiver is the Q of the pickup
coil. Higher Q doesn't produce more signal, but does dramatically
reduce the inband noise levels. The higher the Q, the less noise is
picked up, and therefore the better the SNR (signal to noise radio).
Tiny rods are marginal, but do work. Big rods are much better for
reception. Big loops are even better, but without the ferrite core,
they tend to be huge.

That's the weird part, my Casio watch seems to be the one most likely to
sync up, so long as I orient it right when I go to bed, yet it's a
miniscule antenna.

But having opened some of the "atomic" clocks I have it's also a surprise
that the loopsticks aren't particularly long. Even the wall clock doesn't
ahve a longer loopstick than the portable.

No clue who said it first, but the consensus is that RF is magic.

The object of the antenna is to produce the best possible SNR, not the
strongest signal. If you replace the tiny antenna with a bigger
antenna, the WWVB signal will increase, but so will the received
atmospheric noise level, resulting in no net improvement in SNR. What
will change is the Q (essentially the bandwidth) of the receiver front
end. A low Q wide band loopstick will pickup far more atmospheric
noise than a high Q narrow band loopstick.

Notice how the atmospheric noise (mostly from lightning) increases
dramatically as the frequency goes down:
https://en.wikipedia.org/wiki/Atmospheric_noise
https://en.wikipedia.org/wiki/Atmospheric_noise#/media/File:Atmosphericnoise.PNG

Of course, there's a limit to how small a practical loopstick can be
built. Mostly, the size of the wire to wind the loopstick, its
resistance, and the characteristics of the ferrite material, set the
lower limit. The loopsticks can be made smaller, if you can afford
the fine wire needed to get enough turns.

There's also an upper limit to the size of the loopstick. It's
possible to have such a high Q, that the bandwidth of the WWVB signal
(about 5Hz) will not fit within the loopstick bandwidth. Temperature
and mechanical stability will also be a problem with very high Q
loopsticks. Orientation sensitivity also becomes somewhat of a
problem.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558