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

[Burt I. Weiner]

One thing to keep in mind about modulating with a square wave is that 
you can generate wide spread sidebands, so I'd give some thought to 
rounding it off a bit.  But then the chips were talking about, and 
some are Schmitt Triggers, will change pretty fast and steep.  I 
suspect in the remodulator it's not much of a problem, if at all.

With regards to periods of Diurnal shift, it can get pretty wild in 
amplitude variations, and phase can flip all over due to reflections 
as the big mirror in the sky changes.  Diurnal shift starts to get 
bad about two hours before local sunset and again, not so bad before 
sunrise, and again for a while after sunrise.  Supposedly WWVB 
reception is supposed to be best when it's all daylight between the 
WWVB transmitter and the receiver.  I've always found the WWVB signal 
to be more stable at night.

Someone mentioned that the receiver will not track if the remodulator 
is as little as 1 Hz (cycle) of frequency.  My 8170 has a crystal 
filter in the preamp, so I would imagine it would be extremely 
selective.  I think most, if not all, of the WWVB clocks have crystal 
filters.  The other day when I ordered my crystals I had a choice 
of  60 kHz, 60.002 kHz, 60.005 kHz and 60.000 kHz.  The 60.002 and 
60.005 were only available in Hugh quantity purchases.  The 60.000 
kHz was a little more expensive but I bought 10 of the little buggers 
anyway.  I'll see how close they are when I build the 
remodulator.  Right now I've got some revenue generating work on the 
bench that I need to get out of the way before getting back into the 
fun stuff, but it shouldn't be too long.

Burt, K6OQK


>Subject: Re: [time-nuts] WWVB remodulator for the Spectracom 8170...
>
>Interesting the HC will work all the way down to 2.2V so everything can be
>run from 3 Volts.
>No idea as to the effect of the xtal oscillator maybe the 3.9 M R needs to
>be changed.
>It also appears that the HC chip may doing the lions share of current
>consumption. Spec sheet says up to 20 Ma. Hard to believe actually.
>As for driving lengths of wire over distance it needs to be a buffer chip.
>74hc244. But that seems like serious overkill it can drive 20 ma per port.
>Maybe a cd 4049...
>
>
>On Tue, Jun 18, 2013 at 6:41 AM, Bob Camp <lists at rtty.us> wrote:
>
> > Hi
> >
> > I don't know of any phase tracking receiver that would be bothered by the
> > modulator in Paul's schematic. You could implement it a couple of ways, but
> > the net result would be the same.  The AM is a bit more square wave than
> > the WWVB signal. Modulation depth and timing would / could be dead on.
> >
>snipped...
> > >
> > >       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...



Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California  U.S.A.
biwa at att.net
www.biwa.cc
K6OQK