[Milsurplus] Frequency meters, LM - and BC-

[Bob Camp]

Hi

You can (with some care) measure the frequency of an LM or BC-221 to at least “as good as” the original calibration setup. I came across the frequency standard rack from one many years ago. It was state of the art back then. We’ve moved on.  

The other side of the process is very accurately “spinning the dial”. You can build up a fancy drive setup. Most folks don’t go that far. Without it, it’s *very* tedious to get enough points to do as good a job as they did “back in the day”. The tuning capacitor isn’t quite as linear as one might think ….

Yes, this is really a “that depends” sort of thing. 

Is a cal book that’s “close” good enough? For a lot of things it most certainly is. 

What on earth are we comparing to? 

How accurate is that 80 year old cal book today? Does the meter still have the same tubes in it as when it went through cal? (some very much look like they do). How much does the cal book change when you swap tubes? How long do you keep the unit powered up before you use it? Do you “trust” the crystal or do you zero it with every use? If so how do you do it?

Lots and lots of rabbit holes to wander down. 

Bob

> On Sep 3, 2025, at 1:40 PM, Bill KA8VIT <ka8vit at ka8vit.com> wrote:
> 
> These days you can easily recreate the CAL book using an NanoVNA.
>  
> There was an article posted about it somewhere, (I thought here).
>  
> 73 - BILL KA8VIT / W8COD
>  
> ==================================== 
> Bill Chaikin, KA8VIT 
> Chief Radio Operator 
> WW2 Submarine USS COD SS-224 (NECO)
>  
> ka8vit at ka8vit.com 
> http://ka8vit.com 
> http://www.usscod.org 
> ====================================
>  
>> On 09/03/2025 1:44 AM EDT Bill Pileggi <wpileggi at juno.com <mailto:wpileggi at juno.com>> wrote:
>>  
>>  
>> The LM and BC series frequency meters might be more popular than we think... I had one stolen from my table at the Sellersville, PA hamfest sometime between 2010 and 2020. Absolutely astonished me. The meter did NOT have the CAL book on the front, I had the CAL book with me in electronic format (it's a complicated story as to why I didn't have the physical CAL book (for this serial number) ). The CAL book remains in my electronic archives...
>>  
>> Bill KA3AIS
>>  
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