[Milsurplus] LM freq meter calibration book accuracy

Bill Cromwell wrcromwell at gmail.com
Mon Jul 29 07:27:23 EDT 2013


On 07/28/2013 10:36 PM, John Hutchins wrote:
> My two cents-
> Turn the meter on wait 30 minutes.
> Slap a frequency counter near by and you will note that it rises and 
> falls either side of the mark, setting <= ~100hz on the primary band,  
> by observing the digital frequency counter; Yes is does drift up and 
> down but the drift is slow, over a ~20 minute period.   This may be 
> due to outside air getting into the unit through the phone jack, among 
> other places.  That being said the settings are right on if the 
> reference crystal is adjusted correctly.  I have two LM-13's and two 
> BC221-AK's
>
> I compare this to my HP 8601A the drifts all over the place no mater 
> how long I let it warm up. Setting on the desired frequency in the 
> lower bands is a real challenge to say the least.
>
> Forgot, was it Clete,  who described wrapping the LM or BC221 unit in 
> a heavy towel; that makes a lot of sense.  This would cut down on the 
> air flow exchange with the outside air and limit any drift... I'm 
> going to try this trick on my HP8601A  see if a heavy towel will quiet 
> the drift.  Kind-a like a BBQ smoker.... an even temperature....
>
> Hutch

Hi Hutch,

I should do an evaluation like that with mine. I do know it's well more 
stable and accurate than is required for ham operations. With any 
receive setup I have, if I can get within 100 cps (actually within a 
couple of kc) of your listed net frequency I will most certainly find 
you. Even If I have the bandpass knothole smaller than 100 cycles. Ain't 
panadapter displays wunnerful.

73,

Bill  KU8H






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