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

[ghf at hoffmann-hochfrequenz.de]

Am 2023-06-23 20:58, schrieb Tyler H via time-nuts:

> 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.

I've built a frequency counter based on a Xilinx 2C128 CPLD. It also 
should
fit into a smaller 2C64, i.e. 64 FlipFlops + comb. logic. Unlike a real 
FPGA,
the CPLD keeps its program data in on-chip Flash forever if wanted.
It has an SPI interface to a micro controller (BeagleBoneBlack in my 
case)
The flat cable is the connection to the programmer. The Coolrunner II
family is quite old now. There are cheap Chinese programmers, I was 
told.

The SMAs are RF input and 20 MHz input from a 20 MHz IQD crystal oven.
This board is made on my etching process @ home. (1.5 hours delay from
computer layout finished :-)
There is also a prettier one from commercial fabrication with the OCXO.
The 2C128 should do 100 MHz, the 2C64 should do 200 MHz just so.
I needed only 5 MHz to measure a down-converted X-band DRO.

There are on-board regulators for 3.3V (LT3080) and the 1V8 core 
voltage.

74HCxxx won't work at 100-200 MHz. 74LVC might do.

regards, Gerhard  DK4XP



-------------- next part --------------
A non-text attachment was scrubbed...
Name: 13.png
Type: image/png
Size: 382191 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20230624/4d692748/attachment.png>