[ARC5] The BC-221 low frequency tank circuit puzzle.

[Bruce Long]

If I remember correctly my reading about the history of the early crystal resonator business, 10 ppm was about state of the art in the mid-30's so your hetrodyne detector might have been pretty good for the time.
During WW2 in the hugely expanded crystal resonator industry there was a concentrated effort to get frequency measurements from multiple crystal vendors to agree within a few ppm and that was achieved only by introducing a common, standardized test set and doing round robin testing




      From: Glen Zook via ARC5 <arc5 at mailman.qth.net>
 To: Roy Morgan <k1lky68 at gmail.com>; Leslie Smith <vk2bcu at operamail.com> 
Cc: ARC-5 List <arc5 at mailman.qth.net>
 Sent: Sunday, February 14, 2016 11:15 AM
 Subject: Re: [ARC5] The BC-221 low frequency tank circuit puzzle.
   
I have an RCA TMV-97-C, circa 1935, that goes down to 90 kHz and all the way up to 25 MHz, in 8 ranges, which was sold as a test oscillator and a heterodyne detector.  However, although the dial has extensive calibration marks, the actual calibration is horrible!  That is, the dial only gets one in the neighborhood.  But, I guess that it was "good enough" when it was originally designed.


http://www.njarc.org/books/RCAVictorServiceNotes/ServiceNotes_1935/TMV-97-C_ServiceNotes-1935.pdf



 Glen, K9STH 
Website: http://k9sth.net

      From: Roy Morgan <k1lky68 at gmail.com>
 To: Leslie Smith <vk2bcu at operamail.com> 
Cc: ARC-5 List <arc5 at mailman.qth.net>
 Sent: Sunday, February 14, 2016 8:22 AM
 Subject: Re: [ARC5] The BC-221 low frequency tank circuit puzzle.
   

On Feb 14, 2016, at 8:15 AM, Leslie Smith <vk2bcu at operamail.com> wrote:

> Well done Brian!
> You solved the mystery - that is the "low" range covers 125 to 250kHz;
> the figure in my mind (200 to 400kHz) was simply wrong.

But not completely wrong. The early LM frequency meters (LM-4a through LM-9), and I think their predecessor**  had a (low) frequency range of 195 - 400 Kcs*.  (All LM’s listed in the LM-18 manual I have had the high range of 2000 to 4000 Kcs.)

*The abbreviation/symbol Kcs used in Table 1-4 of the LM-18 manual I have is not in accordance with NIST SP-811, of which I wrote just earlier.  Of course the LM-18 manual predates the international system of units by perhaps some decades.

**The Bendix product brochure from 1941 I have shows their "MODEL IF-21 Portable Frequency Indicator Equipment” which appears to be one of the LM models in civilian form, and its range starts at "125 kilocycles".  But I can’t remember the name/number of the somewhat different 1930’s predecessor to the LM frequency meter. The early BC-221 meters had medium based tubes, later ones had both medium and octal tubes and the latest ones had all octal tubes.  (I “think" that all LM meters had medium based tubes.  At least through LM-19 they did.)

Roy

Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958

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