[time-nuts] WWVB PM Receiver

paul swed paulswedb at gmail.com
Thu Sep 27 18:02:14 UTC 2012


John
Like your thoughts and have exactly tried all that you say over the last 6
months. The div / 2 is a big issue because of the fades and noise. It
really does not work. Now if you are in the 1000uv contour it most likely
mostly will.
By the way limiting was a nightmare.
Regards
Paul.

On Thu, Sep 27, 2012 at 1:41 PM, <johncroos at aol.com> wrote:

> Hello All -
>
> I am new to this forum but have read it for a couple of years. The
> present fulminations on the WWVB format change should be reconsidered
> in the light of prior art. As an old RfFengineer I do not see any issue
> with the format and the business about patents is not really applicable
> as these modulations have been in use since the 1920's.
>
> For one thing the tube analog color TVs managed to have a PLL recover
> the color sub-carrier using less than 10  cycles of the 3.5 mHz color
> burst stuck on top of the horizontal sync pulse. Here we have a
> continuous signal with occasional phase reversals and some amplitude
> steps. This is a much simpler problem that is not begging for
> sophisticated solutions, however much tun they may be to implement.
>
> The following or variations should work.
>
> 1. Receive with a decent antenna but keep the bandwidth such that it
> does not store the phase information.
> 2. Use preselection  with care because the filter is going to have to
> flywheel down and then back up as the phase reverses. This will reduce
> the carrier level during that interval. More bandwidth will shorten the
> time of the ring down-ring up period. The filter must be phase stable
> with temperature.
> 3. AGC with gain may be desired for weak signals. If so implement with
> one of the Analog Devices handy
> dandy VGAs. They provide 50 or more dB of voltage controlled gain with
> absolutely NO phase variation as the gain is changed.
> 4. Now get rid of the short term amplitude variation - for this you
> need a limiter with no AM to PM
> conversion. Again Analog Devices has suitable parts with phase
> variation of less than 5 degrees for more than 70 db dynamic range. The
> AM is now gone.
>
> These parts also output a log of the analog input - so the AM keying
> could be recovered using that if
> desired for some complex sampling scheme.
>
> 5. OK - now you have an amplitude stable BPSK modulated carrier.
> 6. Get rid of the BPSK.
>
> Double the frequency - then divide by 2 and the carrier is recovered
> less the PSK.
>
> For the doubler you may wish to consider a Quadrature Driven Mixer
> Frequency Doubler - has no Hi Q circuits and the output is easily
> filtered. See my article in QEX last year March April.
>
> Or the classic Class C or diode doubler can be used as long as they
> preserve the input phase.
>
> 6a. A Costas Lopp is another classic method that should work fine.
>
> 7. Narrow the bandwidth (say 10 Hz) with a PLL  to clean up the output
> of the doubler. This will get rid of wide band noise and improve the
> SNR. Again the PLL must preserve phase - so some temperature test may
> be a good idea. The PLL also provides a constant level clock to the
> Divide by 2 to avoid phase jitter.
>
> 8. Divide by 2 - and you have a clean 60 kHz signal with no modulation.
> This can the be used for frequency comparison by the phase method or to
> lock up a good local standard.
>
> So it should be possible to implement a receiver without infringing any
> patents and without reams of signal processing code.
>
> Hopefully this is helpful.    -73 John C.Roos  K6IQL  Spring Hill Kansas
>
>
>
>
>
>
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