[time-nuts] If there a FAQ

[Joe]

On Sun, 2010-11-28 at 21:41 -0800, Chris Albertson wrote: 
> WWV at 10MHz is not bad at all.   My current "system" is a cheap
> $0.75 10Mhz crystal tuned with a screwdriver on a veritable trimmer
> capacitor.  I know I can zero-beat  it by ear and get within a couple Hz
> out of 10MHz.  That is better then 1E-6 simply by hand, ear and screwdriver.
> No computer.
> 
> The trouble with a 60Khz signal is that a two cycle error gives
> a 1 in 30K error,
> 
> I'm just looking to use it as a frequency standard, not caring at all about the
> data they transmit
> 
> I figure my first upgrade is to replace the crystal with a temperature
> compensated oscilator chip.   Now to go find one.
> 
Chris, 

It all depends on what your goal is.  A couple of Hertz at 10 MHz will
keep you well within any of the HF ham bands.  

The following addresses beyond the 'Gotta stay in the band' issue.

The problem with the Zero-beat-WWB-at-10-MHz technique is that WWB is
changing frequency.  Not at the transmitter, but on the way to your
receiver. 

The atomic standard synched 10 MHz signal is going thru a process that
adds Doppler shift to your received signal.  

The ionosphere (at HF) is NOT a mirror, but instead is a ever changing
mix of ions that "appears' to change the height at where the reflection
seems to occur.  This phenomena, the change of the apparent path length,
and thus the received frequency, is a form of Doppler shift.

The HF radio time standards CHU, WWV, etc. all suffer from this problem.
There is a Yahoo group, <FMT-nuts at yahoogroups.com>, which has lots of
information on attempts to circumvent this issue. 

WWVB @ 60 KHz offers an improvement in the Doppler problem in that the
propagation at 60 KHz is primarily by groundwave.  

Why would one want to have better accuracy and stability?

FMTs, aka Frequency Measuring Tests, are pre-announced listening
activities where participants attempt to accurately measure the
frequency of signals broadcast in the amateur bands, typically 160 thru
40 meters. 

See <http://www.k5cm.com/> for some examples of what hams and electronic
experimenters have been doing in this area.  Connie and others have been
running tests on a more or less monthly basis. 

Here is one example of a 'good' setup for this activity:

http://www.ve2azx.net/technical/FMT/fmt_info.htm 

A different use.  I personally 'chase' NDBs, Non-Directional Beacons,
attempting to log these low power aircraft navigation aids located
mostly below the AM broadcast band.  Identification of the modulated cw
sidebands normally is within a Hertz or so. 

A review of this lists archives will show many more interesting and
unique times and frequency pursuits. 

It all depends upon what you want to do. 

Joe, K9HDE

PS  The phenomena of two signals beating against each other is called
constructive and destructive interference.  When in phase, you get twice
the signal strength or +3dB, when out of phase, complete elimination of
the signals.