[time-nuts] Re: building a frequency counter.. use 1PPS, ,or 10 MHz reference from GPS?

[Bob Camp]

Hi

These days there are a lot of ways to do things. What’s right depends on a 
lot of issues. 

JLPCB is an outfit in China that will build a PCB and assemble it for you. They
have a selection of parts and you get to pick from their list. That makes for 
some interesting choices. 

https://jlcpcb.com/

A sub $2 MCU with a divider in front of it would be my choice from them. 

Heading back to the GPS side of stuff, it could read out the “sawtooth correction” 
message from a GPS module that sent that message. It would enable you to 
do a pretty accurate counter. 

Bob

> On Jun 24, 2023, at 4:06 PM, Tyler H via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> HP app note 200.   Fundamentals of Frequency Counters.    Thanks!
> 
> http://leapsecond.com/hpan/an200.pdf
> 
> I miss HP.   
> 
> Tyler
> 
> -----Original Message-----
> From: TomH via time-nuts <time-nuts at lists.febo.com> 
> Sent: Saturday, June 24, 2023 12:01 AM
> To: 'Discussion of precise time and frequency measurement' <time-nuts at lists.febo.com>
> Cc: tholmes at woh.rr.com
> Subject: [time-nuts] Re: building a frequency counter.. use 1PPS, ,or 10 MHz reference from GPS?
> 
> Tyler...
> 
> Averaged over a long term, the 1 PPS from a GPS receiver is pretty accurate, but variation from one pulse to the next could be as high a 10 nanoseconds. Any GPSDO with a 10 MHz output uses the 1 PS as its reference since that is the only time signal available from a GPS receiver. The control loop for the 10 MHz ( or whatever frequency) output is designed to clean up that variation so that the variation in the 10 MHz is much less both short and long term. I have probably over-simplified this but that's the basic situation. Conclusion: The GPSDO, say a Leo Bodnar or one of the used commercial models on eBay which can usually be had for under $400, provides a very good time base for a counter. 
> 
> As you mentioned microwave LO's, but only want to measure up to 200 MHz, I am guessing that you plan to measure a low frequency oscillator that is multiplied up and do some math to get the actual LO frequency. There is a very good HP app note from many years ago which talks about all of the considerations in using counters, as well as architectures. Well worth reading if you haven't already found it. Will likely save you some time and headaches, although might reduce the educational value of discovering the pitfalls of various designs yourself. There's nothing like burning your fingers to teach you which end the soldering iron is hot. Up to that point, it's only a theory 😉.
> 
> Hopefully someone on here with better search talents than mine will come up with the URL for it.
> 
> Good luck with your project!
> 
> Tom, N8ZM
> 
> -----Original Message-----
> From: Tyler H via time-nuts <time-nuts at lists.febo.com>
> Sent: Friday, June 23, 2023 2:58 PM
> To: time-nuts at lists.febo.com
> Cc: Tyler H <tyler881 at comcast.net>
> Subject: [time-nuts] building a frequency counter.. use 1PPS, ,or 10 MHz reference from GPS?
> 
> Hello!  
> 
> 
> I'm building a frequency counter for some amateur radio microwave transverters to measure the local oscillators.  
> 
> 
> I am designing towards a capability of directly counting up to 100 MHz and up to 200 MHz with a prescaler.  
> 
> 
> For a time base, I'd like to use a 1PPS pulse from a GPS, but how accurate
> are they?   Should I just count a 10 MHz GPS reference and use that to
> generate a gate for the counter? 
> 
> 
> Yes, there will be propagation delays in dedicated logic gates, but they don't appear to be too bad.  I should be able to get down to 100 Hz or so, which will be fine for what I need to do. 
> 
> 
> I'd rather stick with dedicated counters and gates than move to an FPGA.  
> 
> 
> Thoughts? 
> 
> 
> Thanks!
> 
> 
> Tyler
> 
> KM3G
> 
> Shrewsbury, PA
> 
> 
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