[time-nuts] WWVB Chronverter update progress

paul swed paulswedb at gmail.com
Sat Aug 25 16:35:10 EDT 2018


>From the earlier threads OOK modulation does not work for high end clocks
like spectracoms and truetimes. Have not tried it on the cheapy clocks yet.

I added an external modulator. A dg419 analog switch and then with a few
resistors added DC offset and anttenuation so that the carrier drops by -14
db per the wwvb spec. The logic control is driven from the chronverter and
it totally works. Spectracom Netclock 2 locked up in the normal time.
There are far better modern single supply analog gates that will work. Just
did not have any.

The 60 KHz carrier is supplied by a fluke 6060 generator. This eliminates
any chance of being off frequency and is not the long term answer.

The chronverter actually uses a dallas semiconductor clock chip thats
reasonably accurate.(dangerous to say on time-nuts) So that even if you do
not add the GPS receiver it will run quite some time correctly after
setting the time.

Chronverter draws 6 ma from a 5 V supply. I always like low power.

All in all a very nice answer to what do we do if WWVB goes away.
As mentioned it handles timezones and DST and you can change DST if those
silly politicians screw with it again.

Speculation
The chronverter actually puts out carriers for the popular LF stations
along with the time codes for them.

Though the modulator allows quality clocks to lock I speculate the
frequency from the chronverter is not tight enough. All of these clocks
have very sharp crystal filters in them. 10 Hz. Plan to measure the output
of the chronverter see what the 60 KHz is actually at. Though listening on
a HP3586 receiver it appears pretty close to frequency maybe its just not
good enough. Or the fact is OOK modulation does not work because it gaps
the PLL in these clocks.

Next steps

   - Determine and lay to rest the OOK/need for external modulator.
   - Power amplifier and loopstick transmitting antenna staying at or below
   30uv at 30 meters.
   - Integrate a neo6 GPS receiver in. (Seriously easy)
   -
   - Box it up.

Have my eye on one of the Truetime DC468 units and the classy panelplex
display.

Hope this helps those of you concerned with what to do should WWVB go away.
Regards
Paul
WB8TSL


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