Returnee, interested in Lars GPSDO
(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@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
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@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@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@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
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@lists.febo.com
Sent: 24 December 2022 14:50
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob Camp kb8tq@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@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@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@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com