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W

wb0gaz@yahoo.com

Fri, May 2, 2025 8:33 PM

I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal.

I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun.

My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module.

Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation.

The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice.

Thanks for any reading resource pointers,

73 Dave WB0GAZ wb0gaz@yahoo.com

I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal. I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun. My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module. Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation. The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice. Thanks for any reading resource pointers, 73 Dave WB0GAZ wb0gaz@yahoo.com

CE

chris elfpen.com

Mon, May 5, 2025 3:53 PM

I acquired the board and built the implementation from the attached QEX article.
It seems to work. I know it has been discussed on this board quite a bit and has it's faults.

https://ve2zaz.net/GPS_Std/Downloads/VE2ZAZ_GPS_Derived_Std_QEX_09_10_2006.pdf

From: wb0gaz--- via time-nuts time-nuts@lists.febo.com
Sent: Friday, May 2, 2025 3:33 PM
To: time-nuts@lists.febo.com time-nuts@lists.febo.com
Cc: wb0gaz@yahoo.com wb0gaz@yahoo.com
Subject: [time-nuts] Looking for simple/beginner's design guide for experimental construction of GPSDO (1 PPS controlling 10 MHz) 5/2/2025

I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal.

I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun.

My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module.

Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation.

The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice.

Thanks for any reading resource pointers,

73 Dave WB0GAZ wb0gaz@yahoo.com

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

I acquired the board and built the implementation from the attached QEX article. It seems to work. I know it has been discussed on this board quite a bit and has it's faults. https://ve2zaz.net/GPS_Std/Downloads/VE2ZAZ_GPS_Derived_Std_QEX_09_10_2006.pdf ________________________________ From: wb0gaz--- via time-nuts <time-nuts@lists.febo.com> Sent: Friday, May 2, 2025 3:33 PM To: time-nuts@lists.febo.com <time-nuts@lists.febo.com> Cc: wb0gaz@yahoo.com <wb0gaz@yahoo.com> Subject: [time-nuts] Looking for simple/beginner's design guide for experimental construction of GPSDO (1 PPS controlling 10 MHz) 5/2/2025 I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal. I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun. My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module. Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation. The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice. Thanks for any reading resource pointers, 73 Dave WB0GAZ wb0gaz@yahoo.com _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

BC

Bob Camp

Mon, May 5, 2025 4:47 PM

Hi

With the most simple approach using just a basic 1 pps output on a run of the mill GPS module:

You take the 10 MHz counter result as strobed by the 1 pps. The target 10 MHz frequency is subtracted from that result. The error is how far off that result is. The error is scaled and applied to the OCXO EFC via a DAC each second. Not a lot involved doing this.

Your OCXO will be less stable than it would be without the GPS involved. This would be true out to pretty long time spans. ( The OCXO likely is moving more second to second than it should in a week …)

Is this a “good enough” outcome for the project?

Bob

On May 2, 2025, at 4:33 PM, wb0gaz--- via time-nuts time-nuts@lists.febo.com wrote:

I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal.

I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun.

My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module.

Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation.

The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice.

Thanks for any reading resource pointers,

73 Dave WB0GAZ wb0gaz@yahoo.com

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi With the most simple approach using just a basic 1 pps output on a run of the mill GPS module: You take the 10 MHz counter result as strobed by the 1 pps. The target 10 MHz frequency is subtracted from that result. The error is how far off that result is. The error is scaled and applied to the OCXO EFC via a DAC each second. Not a lot involved doing this. Your OCXO will be *less* stable than it would be without the GPS involved. This would be true out to pretty long time spans. ( The OCXO likely is moving more second to second than it should in a week …) Is this a “good enough” outcome for the project? Bob > On May 2, 2025, at 4:33 PM, wb0gaz--- via time-nuts <time-nuts@lists.febo.com> wrote: > > I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal. > > I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun. > > My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module. > > Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation. > > The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice. > > Thanks for any reading resource pointers, > > 73 Dave WB0GAZ wb0gaz@yahoo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

EK

Erik Kaashoek

Mon, May 5, 2025 5:12 PM

Go to EEVBLOG and search for "Lars GPSDO"
Read all the documentation Lars did write
Erik.

On 2-5-2025 22:33, wb0gaz--- via time-nuts wrote:

I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal.

I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun.

My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module.

Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation.

The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice.

Thanks for any reading resource pointers,

73 Dave WB0GAZ wb0gaz@yahoo.com

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Go to EEVBLOG and search for "Lars GPSDO" Read all the documentation Lars did write Erik. On 2-5-2025 22:33, wb0gaz--- via time-nuts wrote: > I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal. > > I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun. > > My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module. > > Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation. > > The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice. > > Thanks for any reading resource pointers, > > 73 Dave WB0GAZ wb0gaz@yahoo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

JL

Jim Lux

Mon, May 5, 2025 5:39 PM

Aside from the copious information in the archives of this list (!).. I'd take a look at Brooks Shera's GPSDO and how it evolved.
If you search for "shera GPSDO" you'll get some hits

here's the original article: https://www.qsl.net/n9zia/wireless/QST_GPS.pdf

https://k6jca.blogspot.com/2019/02/an-arduino-version-of-brooks-sheras.html has a lot of useful info (including a simulink model, and lots of analysis)

On Fri, 2 May 2025 20:33:45 +0000 (UTC), wb0gaz--- via time-nuts time-nuts@lists.febo.com wrote:

I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal.

I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun.

My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module.

Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation.

The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice.

Thanks for any reading resource pointers,

73 Dave WB0GAZ wb0gaz@yahoo.com

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Aside from the copious information in the archives of this list (!).. I'd take a look at Brooks Shera's GPSDO and how it evolved. If you search for "shera GPSDO" you'll get some hits here's the original article: https://www.qsl.net/n9zia/wireless/QST_GPS.pdf https://k6jca.blogspot.com/2019/02/an-arduino-version-of-brooks-sheras.html has a lot of useful info (including a simulink model, and lots of analysis) On Fri, 2 May 2025 20:33:45 +0000 (UTC), wb0gaz--- via time-nuts <time-nuts@lists.febo.com> wrote: I'm curious to learn-by-doing about GPSDO architecture/implementation, starting with a GPS receiver module (on hand already) that has 1 PPS output signal. I suspect this can be a complex undertaking and ill-advised ("why would you build when you can buy?"), but this is about experimentation for fun. My starting point idea is this - a 10 MHz OCXO (which can be frequency-trimmed by a small DC voltage) feeding a 24-bit counter whose count is read by a microcontroller, then reset and re-armed ready for the next the 1PPS signal from GPS module. Looking for a pointer to a write-up (PDF or web page preferred, I've never enjoyed trying to learn from youtube videos) that would help guide my experimentation. The outcome would certainly not need to be high-specification; just something that implements 1 PPS leading to control over a 10 MHz oscillator using a microcontroller would suffice. Thanks for any reading resource pointers, 73 Dave WB0GAZ wb0gaz@yahoo.com _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

W

wb0gaz@yahoo.com

Mon, May 5, 2025 6:41 PM

Thank you both - I hadn't found either article previously, and both look promising.

Should be able find the W5OJM article in ARRL QST archives (which I very occasionally have consulted, with good results.)

Thanks!

Dave

On Monday, May 5, 2025 at 09:53:28 AM MDT, chris elfpen.com chris@elfpen.com wrote:

I acquired the board and built the implementation from the attached QEX article.
It seems to work. I know it has been discussed on this board quite a bit and has it's faults.

Thank you both - I hadn't found either article previously, and both look promising. Should be able find the W5OJM article in ARRL QST archives (which I very occasionally have consulted, with good results.) Thanks! Dave On Monday, May 5, 2025 at 09:53:28 AM MDT, chris elfpen.com <chris@elfpen.com> wrote: I acquired the board and built the implementation from the attached QEX article. It seems to work. I know it has been discussed on this board quite a bit and has it's faults.