[time-nuts] 1PPS to 32.768 khz

Bill Hawkins bill.iaxs at pobox.com
Wed Oct 19 00:57:32 EDT 2016

Hi Lee,

We all had a first time posting on this list and survived it. No

You need to know more about phase locked loops. In this case, you need a
voltage controlled crystal oscillator that a simple binary divider can
take down to 1 PPS. That 1 PPS is compared to the GPS 1 PPS with a
simple flip-flop, which produces a pulse width that can be filtered to
be the control voltage for your VCXO. The resulting feedback loop causes
your VCXO to track GPS.

Now then, this is a great oversimplification of the process for getting
very low timing errors. However, human time constants for observation of
a clock do not require very low timing errors. Very few people would
notice a 50 millisecond error. 

To get a useful answer from this group, you need to specify the accuracy
required. If you want picosecond errors, you are into big bucks.
Nanosecond errors are expensive but can be found on eBay. Microsecond
errors still need a good GPS receiver (not cheap). Millisecond errors
are not normally the subject of this group, although there has been a
thread on receivers barely capable of that.

Lurk and learn, grasshopper. The cost is low until you decide on the
level of accuracy you wish to reach.

Best regards,
Bill Hawkins

P.S. I was afflicted with the desire for accuracy down to the Caesium
standard level. Hydrogen masers remained beyond my means. Now I live in
an apartment in an old folks community, which required severe
downsizing. The return on investment was negative. The older I get, the
less I require precision time. YMMV.

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Lee -
N2LEE via time-nuts
Sent: Tuesday, October 18, 2016 9:03 PM
To: time-nuts at febo.com
Subject: [time-nuts] 1PPS to 32.768 khz

First let me say this is first time I have posted to the group so go
easy on me. :) Secondly I want everyone to know that you guys make me
feel so NORMAL for wanting to use and understand accurate timing

I thought there was something seriously wrong with me now I know there
are others affected with the same disease. hehe

Now my questions.

1. Does anyone know of a device that will take a 1PPS GPS timing signal
and generate a 32.768 kHz sine wave output ?
I have big digital clock that uses an 8 bit micro processor and an
external 32.768 crystal. Obviously the external crystal is awful for

I have searched every where using as many search terms as I can think of
and can't believe there is not a device that performs this function.

I have found a couple of Epson RTC chips that might come close that 1pps
but I don't think that corrects the 32khz just the clock time.

2. 10 Mhz Freq Standard
I am not in the same league as the majority of the list members and just
starting to dabble in GPSDO stuff.
I have tried to find a thunderbolt as a starting device but it appears
those are either dried up or people want too much money.

I wanted to get the opinion of anyone who has tried the Leo Bodnar GPSDO
For the money it appears to offer a beginner a lot of features.

Thanks and reading the daily digest of what you guys are working on.
I have a feeling if I am not careful you guys could cost me a lot of
money. hehe


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