[time-nuts] WWVB Chronverter update progress

Bob kb8tq kb8tq at n1k.org
Sat Aug 25 17:31:32 EDT 2018


You can do the 14 db deep modulation with a tristate gate and a pair of resistors. 
Ground the input and feed the “modulation” signal to the tristate control. 


> On Aug 25, 2018, at 4:35 PM, paul swed <paulswedb at gmail.com> wrote:
> 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
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