[Milsurplus] LM freq meter calibration book accuracy

[John Hutchins]

Group, Bill  -

The reference Crystal to be aligned in a room @ 68F or 20C  air;  I got 
that spec somewhere:-/

Now the measurements I made were in a room of relativity stable air,  in 
doors with Central HVAC. No ceiling fan going.  Warmup at least an 
hour.  I made a Xcell spread sheet at all the setting points

Movement off the set frequency was slow and gentle,  I observed an 
recorded whole cycle of drift over an hour or so by hand popping in and 
out every 5 minutes or so.

After 65 years I was impressed.

Hutch



On 7/29/2013 6:27 AM, Bill Cromwell wrote:
> 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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