[time-nuts] WWVB remodulator for the Spectracom 8170...

[David I. Emery]

On Mon, Jun 17, 2013 at 06:11:15PM -0400, Bob Camp wrote:
> Hi
> 

> The Costas loop already has the AM component available. There's no
> need for a second receiver, just wire the AM output over to the output
> modulator.

	That is standard for most Costas loops with an I arm... haven't
looked at his schematics carefully yet... possibly one might need some
kind of AGC to use it as input to  a second double balanced mixer
serving as modulator in order to get the right 14 (?) db AM as signal
fades slowly.   Not sure how deep the diurnal fades are...

	But I guess if everything is quite linear over enough of a range
one could perhaps just remodulate without AGC and create a replica of
both the modulation and fades on  the local 60 KHz carrier.




> 
> Bob
> 
> On Jun 17, 2013, at 5:57 PM, "David I. Emery" <die at dieconsulting.com> wrote:
> 
> > On Mon, Jun 17, 2013 at 02:41:13PM -0700, Burt I. Weiner wrote:
> >> Chris,
> >> 
> >> The 8170 was originally intended to be a frequency reference source 
> >> tied to the USFS (United Stated Frequency Standard).  It also gave 
> >> the time of day, but I believe that wasn't it's primary purpose.  As 
> >> I recall, there were some versions that did not have the clock 
> >> readout and some that had a chart recorder.  Back in the 80's I used 
> >> to drool (it was a disgusting sight!) over the Spectracom receivers 
> >> with the chart recorders.  At that time I was usuing a Gertsch RLF-1 
> >> with an external Moseley 680 chart recorder.  The remodulator 
> >> precludes it from being used as a frequency standard, but in my 
> >> opinion, so does the fact that WWVB is now phase shifted a bunch.
> >> 
> >> The 8170 uses a coherent detector and that's where the problem 
> >> lies.  While the 8170 still locks to the WWVB carrier, the new BPSK 
> >> scheme causes the detector to output bad data in spite of the 
> >> original dips in the carrier still being present.  I had always 
> >> wondered how it was able to pull the data out the noise, but never 
> >> had a manual until just recently.  I had naively assumed that the 
> >> WWVB new BPSK scheme would not affect the time of day aspect of the 
> >> 8170.  Like I said, I only use it as a clock in my shoppe, and being 
> >> an old dog I don't easily learn new tricks such as looking in a 
> >> different direction for one of the other clocks.
> > 
> > 	I suppose I am stating the obvious, but why not combine Paul
> > Swed's Costas loop and this scheme to output a phase locked 60 Khz 
> > with the right AM modulation ?
> > 
> > 
> > 
> > -- 
> >  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
> > "An empty zombie mind with a forlorn barely readable weatherbeaten
> > 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> > celebration of what could have been, but wasn't and is not to be now either."
> > 
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-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."