[time-nuts] WWVB remodulator for the Spectracom 8170...
David I. Emery
die at dieconsulting.com
Mon Jun 17 21:29:25 EDT 2013
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."
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