[time-nuts] Re: Returnee, interested in Lars GPSDO

[john.haine at haine-online.net]

Thanks everyone for the comments.  I have ordered a PCB for the unit from a gentleman in Holland so will go ahead with the standard design.

Cheers, John.

-----Original Message-----
From: Bob Camp via time-nuts <time-nuts at lists.febo.com> 
Sent: 24 December 2022 14:50
To: Discussion of precise time and frequency measurement <time-nuts at lists.febo.com>
Cc: Bob Camp <kb8tq at n1k.org>
Subject: [time-nuts] Re: Returnee, interested in Lars GPSDO

Hi

My point was, you have a CPU and various other chunks of hardware running around. 
There are a wide range of ways to convert that pulse to “something else” ( like a voltage to feed the A/D) . 

You also could go over to a <$10 RP2040 and get a lot more mileage out of your “something else”. 

Bob

> On Dec 23, 2022, at 8:13 AM, Jim Harman via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> (I originally sent this just to Bob, repeating for the group) The 
> "something else" in Lars's design is provided by 5 MHz derived from 
> the oscillator, which feeds a timer in the processor.  The 1 pps 
> triggers a "timer capture" which records the number of 5 MHz cycles 
> since the last pps with a resolution of 200 nsec.  (The Arduino 
> processor clock is 16 MHz and the maximum timer frequency is Fclk/2, 
> so you can't drive the timer with 10
> MHz.)
> 
> This coarse detector is used to extend the lock-in range and achieve 
> the initial lock. It would be possible to make a GPSDO with just this 
> detector, but the phase sensitivity would be low. The 4046 followed by 
> the pulse width to voltage converter and the processor's 10 bit  A/D 
> converter reads the phase with a resolution of about 1 nsec.
> 
> 
> On Thu, Dec 22, 2022 at 8:40 PM Bob Camp <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> Since you only get one sample per second, no matter what you do, why 
>> bother with the 4046 at all? 1 us will roll over at 1 ppm off 
>> frequency ( which is very possible with an OCXO ). You still need 
>> “something else” to get things close.
>> 
>> Bob
>> 
>> 
> --Jim Harman
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com To unsubscribe send 
> an email to time-nuts-leave at lists.febo.com
_______________________________________________
time-nuts mailing list -- time-nuts at lists.febo.com To unsubscribe send an email to time-nuts-leave at lists.febo.com