[Lowfer] frequency counter calibration

[Bill Cromwell]

On Sat, 2013-01-26 at 11:49 -0800, Ed Phillips wrote:
> Bill:
> 
>     Here is the question your note raises for me:  EXACTLY how do YOU
> do this with YOUR 2810?  Mine, which has been in use here since they
> first came out much more than 10 years ago, now reads 2 Hz low when I
> measure my 10 MHz Rubidium standard, indicating that the reference
> oscillator is high by 2 parts in 10 million after more than 10 years
> of aging.  Pretty good in my opinion, but off topic as far as 'your
> method' is concerned.  Question:
> 
>     HOW do YOU 'connect the counter's clock generator' to ANYTHING
> without removing the case [a job I wouldn't wish on my worst enemy
> although necessary when replacing battery], digging around to find an
> unmarked spot on the circuit board where the reference signal is
> available AND not subject to loading by an external connection????
> How do you know there's no loading?  I'm speaking of an
> Optoelectronics 2810 counter, not some generic device.  With mine, and
> I suspect all others, there is no trace of the 10 MHz reference
> present at the antenna terminal.
> 
> Ed   

Hi Ed,

If it's really that tough just drive your frequency counter with a
signal generator that has been zeroed to WWV and then make the frequency
counter read the correct frequency. That's the one I outlined using an
AM broadcast transmitter. You could also just tweak it to display the
correct frequency of your rubidium clock. Presumably you were able to
read that without yanking the clock oscillator too far off and with the
case in place. Pretty easy. It's so easy that even *I* can do it.

The frequency counter clock - that 10 MHz xtal oscillator with heaters
and GPS spankers - provides the counting gate timing. All you are doing
is setting the gate timing. You can do it 'forward', 'backward', or
'sideways' and the result will be the same. If the counting chain is
defective and the clock oscillator is spot on, the result will always be
trash, too. So looking at it several ways for a reality check is good.
If you have set it with your atomic clock and then used it to check WJR
in DeeTroyt and find WJR at 600 kHz, yer counter is broke. Etc. If you
find it at 760 kHz...A-ok.

73,

Bill  KU8H