Trevor Wilson wrote:

-------------------

mike wrote:
Phil Allison wrote:



** Anything using a crystal time base will have good accuracy.



I don't expect anything I could say would change your mind.
We'll just have to disagree on that.



**Here is a crystal I specified for a project back in the 1990s (because
it was cheap). I paid AUS$0.22 each for them in 1,000 quantity. It's
cheap because it is typically used in clocks.

http://au.element14.com/ael-crystals...mhz/dp/9509585

Here is the technical data:

http://www.farnell.com/datasheets/31...801.1495964215

+/- 20PPM is very decent accuracy. Plenty good enough for regular
domestic service. Certainly, for professional stuff, you'll need an oven
for the crystal.


** Please note that the tempco of 50ppm over the range of -10C to 60C.

So well under 1ppm per degree C !!!

The initial accuracy can easily be trimmed to under 1ppm match the usual operating temp - say 20 C.

Put those simple facts together and it ain't difficult to get 5ppm accuracy in your workshop.

Just don't put the X-tal next to a hot component on the PCB - like Jim Rowe of EA did with their 1GHz counter.




..... Phil