[Milsurplus] Frequency Measurement test

[Howard Holden]

There are those of us who still use the BC-221 or it's Navy cousin the LM, 
which comes in many flavors.

In the early 90s I participated in an FMT and came within 47 Hz (repeatedly) 
with a BC-221. With no help from a freq counter.

I've had an LM sans calibration book for years now. The lack of the book 
might be viewed by some as a hindrance, but I've made my own calibration 
settings for the 3500-3700 segment (I'm not into phone so no loss for me) 
with the use of a calibrated freq counter and some patience. It isn't hard, 
just a little tedious. But it's quite accurate, and I can come within less 
than 100 Hz using my cal table, the interpolation scale on the LM,  and some 
additional interpolation between the dial-to-Khz  settings.

The BC-221 and LM are quite similar, some differences in control functions, 
and the LM has no modulation, and is usually designed to run with an 
external supply, with internal regulators, while the BC is usually a 
battery-operated affair, although many have been converted to AC supplies.

Problems I've found are bad calibration crystals, sketchy connection in the 
BC from it's output to the antenna post, and on a BC with the cal book I 
just picked up, it doesn't keep calibration over a page of the book. I think 
there's an issue with a fixed capacitor in parallel with the tuning cap.

The BC is rated at a frequency accuracy of less than 500 Hz near a 
calibration point, and less than 750 Hz well away from the point. I find 
them, with a little care to be far more accurate than that. You just have to 
be willing to calibrate out the long-term slight drift downward, and focus 
on precision in dial settings.

The fact they're seventy-something year-old devices and can still maintain 
such accuracy and stability is nothing short of amazing, and they're keepers 
for me. Especially the LM which I think is a better-designed unit.

Howie WB2AWQ





-----Original Message----- 
From: Ray Fantini
Sent: Tuesday, November 03, 2015 10:26 AM
To: milsurplus at mailman.qth.net ; MRCA at mailman.qth.net
Subject: [Milsurplus] Frequency Measurement test

No matter how improbable it appears once again a picture and reference to 
WW2 military technology and equipment has appeared in this month's issue of 
QST, a magazine almost entirely consumed with pushing the modern Ham to 
spend all their money and time that is when not supporting the league itself 
in buying the latest new radio widget.  In the announcement about the annual 
frequency measurement test there is a little sub article and picture of the 
BC-221 with a write up on how that was once the state of the art in 
frequency measurement. They further challenge modern Hams to try using that 
old heterodyne technology and enter their results along with a write up 
about it use. So here it is, an opportunity for some of the "know it all's" 
out there to demonstrate their competence with the two twenty one in 
comparison with the state of the art Hams who will just park the cursor over 
the carrier on the display and write the number down from off the screen. 
Myself I am not quite smar
t enough in such matters being I will just take a signal source like a 
BC-221 and heterodyne it against an unknown carrier and then use a frequency 
counter like my old HP-5328 to read the frequency.

Ray F/KA3EKH
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