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Old April 21st 16, 04:09 PM posted to rec.radio.amateur.moderated,rec.radio.amateur.homebrew
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Default Time and Frequency References

rickman wrote:
On 4/20/2016 12:01 PM, Rob wrote:
rickman wrote:
On 4/18/2016 5:43 PM, David Woolley wrote:
On 18/04/16 15:39, rickman wrote:
How important are time and frequency references to amateur radio
operators? I've been working on a radio controlled clock design that
would be capable of generating a 32.768 kHz, 60 kHz, 240 kHz, 1 MHz and
10 MHz frequency references in addition to providing the time and date.
Initially it would be capable of receiving the 60 kHz transmissions of
WWVB and MSF. With minor tweaks other stations could be received.

Would this be useful to others?


Anyone who wants high accuracy off air time and frequency standards
would use GPS these days. Even that is almost two decade old technology
in amateur radio usage: http://www.tapr.org/kits_tac2.html

Is there something about GPS that is inherently superior for a frequency
reference? For setting a time, GPS can provide a smaller offset, but I
don't see where it has any advantages over WWVB or similar station
broadcasts where you can receive them.


The direct-sight UHF radio link provides less jitter and uncertainty
than the VLF signal that suffers from propagation effects.


That is important if you are looking for microsecond timing. But it has
very little impact on use as a frequency reference.


It depends on the stability of your oscillator and the integration
time that you can use as a result of that. Short-term frequency accuracy
is not much different from accurate timing.

The main limitation of a GPS receiver is the need for an outside antenna
for many installations. A WWVB receiver is self contained and much
lower cost.


Sure it can be easier to place an antenna for a VLF station, but on
the other hand there is much more interference, mainly from switchmode
powersupplies these days (in the old days it was from CRT computer
monitors), but also from lightning.


I guess you aren't familiar with the extremely narrow band timing
signals, 1 bps. I'm working on a receiver with a 30 Hz bandwidth to
exclude environmental noise.


I have experience with receivers for DCF77, which is a similar station
to MSF and WWVB. The frequency is 77.5 kHz.
Of course the results depend on the quality of the receiver.
I use some receiver modules from "atomic clocks" but I also have a
somewhat better receiver which has a crystal lattice filter.
I need to find a good spot for the antenna, away from certain equipment,
for it to work well. E.g. I had a problem with a switchmode powersupply
I used for the station in the past, which is switching at around 25 kHz.
The third harmonic (which of course drifts around depending on load and
temperature) interfered with the DCF77 receiver when it is within about
3 meters. I now have a different supply and this problem is gone, but
of course that is just coincidence.
Older CRT monitors for computers also emit quite a strong field in this
frequency range. Fortunately the frequency is quite stable, so it is
either OK or it is a problem, and it could be solved by changing the
display parameters.
Finally, when there are thunderstorms around, the signal often becomes
undetectable due to the many interference bursts.


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