[time-nuts] WWVB Chronverter update progress

ed breya eb at telight.com
Tue Aug 28 19:11:30 EDT 2018


Paul,
If you're going to reference it from a GPSDO anyway, why worry about a 
TCXO reference (and power too, for that matter). You can easily make the 
60 kHz from the 10 MHz.

For example, with two 74HC390s and a 74HC86 you can make 50 kHz and 10 
kHz and mix them with one EXOR section of the '86 to have 60 kHz 
available. Some fairly simple bandpass filtering should select and clean 
it up sufficiently. Two other sections of the '86 can be set up as 
inverters and self-biased as amplifiers - one to convert the 10 MHz sine 
reference to logic, and the other from the filter output to logic, if 
needed. And, you'd still have a divide by 5 and an EXOR left over to 
fool around with.

The same parts and process can be done at a higher frequency and then 
divided down afterward. (5+1) MHz/100, and (500+100) kHz/10 would work 
too. It depends on what frequency you prefer for the BPF. If you go high 
at 6 MHz, you then have the option to make a crystal filter from readily 
available parts.

Going the high way also provides for higher logic frequencies that are 
more or less in sync, in case you want to do any I-Q modulation type 
stuff - you can even use synchronous counters instead, to really make sure.

Overall, I think I'd recommend going at 5+1= 6 MHz, filtering with 6 MHz 
crystals, then dividing down to 60 kHz, with 2f and 4f clocks available 
for I-Q use. I sketched out a quickie circuit that's quite simple and I 
think would do. It would take two HC390s for the dividing, as before. 
Each HC390 is two divide by 10 counters, including a 1/2 and 1/5 in 
each, usable separately. So, with two parts, there are four 1/5s and 
four 1/2s available.

Here's a verbal process description: 10 MHz sine convert to logic with 
HC86, 10 MHz/2=5, 10 MHz/10=1 with first HC390, add 5+1=6 with EXOR, BPF 
6 MHz, convert to logic with HC86, 6 Mhz/25=240 kHz=4f, 240/2=120 
kHz=2f, 120/2=60 kHz=f, with second HC390.

Ed



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