[time-nuts] If there a FAQ
jfor at quik.com
Wed Dec 1 04:12:10 UTC 2010
> 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
> 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.
This is why I suggested a method of using a digital averaging scope to
look at the WWV pips and watching them "walk" several days ago. Phase
tracking is unreliable at best, IMO, at HF.
> 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:
> 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.
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