[time-nuts] WWVB Chronverter update progress
paulswedb at gmail.com
Tue Aug 28 21:33:54 EDT 2018
LPF filter added 2.2mH choke to a .0022uf cap 1K R pretty simple and
anttenuators and isolation to drive up to 4 receivers.
Have not looked at the power amp and loops stick antenna yet. But it really
is time for GPS a neo.
Looking very good.
On Tue, Aug 28, 2018 at 7:29 PM, paul swed <paulswedb at gmail.com> wrote:
> Ed appreciate the details but no intent to generally run a GPSDO in fact
> the 5 V @ 50 ma is a serious power pig. The chronverter draws 5 ma. Clearly
> the TTL is a heater. Chuckle. I do want to drive the chronverter with GPS
> as its designed for.
> Whats pretty interesting is you can adjust its offset. I just jammed time
> into it several days and its been fairly good with power ups and down. Its
> impressive. Though not in an ultimate time-nuts way.
> GPS just assures it is accurate. But there is a lot of flexibility.
> Main goal of this whole project is to replace wwvb if it goes away. If it
> does the project doesn't even have to run 24/7. Fire up at 10 pm to 3 am
> and power down. Thats enough to set my wall clocks for a day. Its just nice
> to know it can also set the spectracoms and Truetimes. Icing on the cake.
> I am impressed with what Dave did with the 8 pin pic. He has all of the LF
> time signals in there. (No wwvb BPSK though) DSTs settings, zone offsets,
> half zones, etc.
> Just looking at low pass filters for the 60 KHz ttl out right now. Simple
> LR or RC. Since this particular output feeds coax to the quality receivers
> I don't need to be that careful. Its working great without any filtering.
> Reality if it draws little power I will let it run 24/7 but then you just
> have to stick a display on at that point.
> On Tue, Aug 28, 2018 at 7:11 PM, ed breya <eb at telight.com> wrote:
>> 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.
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