[Lowfer] frequency counter calibration

[Ed Phillips]

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  

Bill Cromwell wrote:

>On Fri, 2013-01-25 at 23:10 -0800, KD7JYK DM09 wrote:
>  
>
>>: > ways (shouldn't be very much). I will set it to agree with WWV at 10 MHz
>>: > and send it back to you.
>>
>>How is this done?  optoelectronics told me years ago people do this, they 
>>said they didn't know how.
>>
>>Kurt 
>>    
>>
>
>Hi Kurt,
>
>It seems incredible that the folks at Opto "don't know how". You need
>some kind of receiver that can detect zero beat. Zero beat is not the
>tone that matches your sidetone! Many newer (and not so new any more)
>receivers have a severe rolloff in response below 500 or 300 cycles per
>second. Even if the lowest frequencies are severely suppressed you might
>still be able to detect zero beat. If not...you will have to tap into
>the detector output before the audio stage (perhaps at the top of the
>volume control). You will be using AM of course and the carrier must be
>somewhere in the IF passband.
>
>Use the heterodyne frequency measurement techniques. There are a number
>of ways to approach it. I would most likely lightly couple the counter's
>clock generator at 10 MHz to the receiver set on 10 MHz WWV and then
>measure the zero with a scope. Human hearing will NOT be able to hear
>anything at all near zero beat so some means has to be used to detect it
>other than by ear. On some receivers you can watch the S-meter wobble
>near zero beat or even hear the AGC pumping. The response will slow to
>nothing (zero) and then increase again after zero is passed. I would use
>my O'scope. It will be the counter's clock that is tuned and NOT the
>radio. It should go without saying but all of the gear used should have
>a substantial warmup time - an hour of more. Overnight is *good*.
>
>There are other known signals that can be used. If you are unfamiliar
>with heterodyne frequency measurement look up the the LM or BC-221
>manuals. The method is very accurate for setting an oscillator to a
>known standard. WWV *IS* a known standard. Once the frequency counter
>clock is zeroed it serves as a secondary standard with the nice feature
>of automatically interpolating between multiples of the secondary
>standard and displaying the results on the digital readout. An AM
>broadcast station can be used (the tolerances may not be as tight as
>WWV). Drive the counter with the signal generator. Set the signal
>generator to zero with BC transmitter. Then set the counter's clock so
>that it reads the transmitters (known) frequency. You can use any
>acceptable standard including GPS, WWVB, your rubidium or cesium
>standard. How accurate you want your Opto to be is up to you. Optos are
>NOT temp compensated unless you modify them. I'm an amateur and my
>license even says so. WWV is probably good enough for most of what I
>will be doing. I check my secondary standards against WWV often. They
>seem to stay spot on of the time...sometimes for years.
>
>On those LMs .. heterodyne frequency meters can do several very handy
>tricks that your frequency counter can NEVER EVER do. It's good to have
>those tricks available in addition to a digital frequency counter. Maybe
>the technical people at Opto are all very young and missed the boat for
>alternative means and the advantages of alternatives. I could use one of
>my LMs to zero against WWV and then zero the counter's clock against the
>LM. So many choices.
>
>Did this answer your questions? Did it raise more questions?
>
>73,
>
>Bill  KU8H
>
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