[time-nuts] Vintage Frequency Measurement

Bill Byrom time at radio.sent.com
Sun Feb 12 23:02:58 EST 2017


The BC-221 was mentioned in a Time-Nuts thread from December, 2015.
Copying from my post in that old thread:

Back in the early 1970's I took my BC-221 and added a TTL divide by
1,000 (or 2,000 or 4,000 or 8,000) external circuit to generate very
precise audio test tones from the RF oscillator. The BC-221 had two
output frequency ranges: LOW: 125 to 250 kHz HIGH: 2 to 4 MHz  By using
the appropriate range and divide ratio I could generate 15.625 Hz to 4
kHz (and multiples) with very smooth continuous tuning and great
accuracy (typically better than 0.005%). This was very useful for
adjusting and measuring audio filters and circuits, such as 2125/2295
Hz AFSK terminal units I was using on 2 Meter AM and with SSB rigs for
HF FSK. I could tune up my filters built with 88 mH telephone surplus
toroidial inductors. I could also use the audio source to compare by
ear the beat note between harmonics of my divided-down 5 MHz commercial
surplus precision oven oscillator and RF signals (such as during the
ARRL Frequency Measuring Test).  The anti-backlash gear mechanism,
large dial with high resolution interpolation scale, and well-built
variable capacitor were difficult to find in other commonly available
radio related equipment. In my opinion the BC-221 was a technically
beautiful precision instrument. It was the time-nuts tool of choice for
several decades!
--

Bill Byrom N5BB







On Sun, Feb 12, 2017, at 08:31 PM, Bob Camp wrote:

> Hi

> 

> If you look at a typical BC-221 in use, it goes from “calibrated” in a
> nice warm hut to the back

> of a jeep. It heads out to an ice cold flight line and the
> switch turns
> the batteries back on again.

> It bumps in and out of a batch of B-17’s setting each one up for the

> day’s net frequencies. You

> would be doing very well to hold 50 ppm under those
> circumstances. That
> was indeed adequate

> for the purpose.

> 

> Bob

> 

> 

>> On Feb 12, 2017, at 7:58 PM, Bob Albert via time-nuts <time-
>> nuts at febo.com> wrote:
>> 

>> Well 5 cycles per second is more than accurate enough.  That
>> translates to a 150 Hz error at 30 MHz, definitely negligible for the
>> uses of all these gear.  There was no official Time Nuts group at the
>> time, although many of us had the spirit.  Yet the capability of the
>> BC-221 far exceeded its specification if you could receive WWV.
>> 

>> I noted immediately that zero beat of WWV at 5 MHz was not as precise
>> as at 15 MHz.  In those days there was even a 30 MHz WWV but it got
>> shut down a long time ago.  And there were CHU and JJY.
>> 

>> Bob

>> 

>> 

>>   On Sunday, February 12, 2017 4:02 PM, Dan Rae <danrae at verizon.net>
>>   wrote:
>> 

>> 

>> To put BC-221 things in perspective, the 1 Mc/s reference crystal was
>> adjusted, according to the manual, to within 5 c/s...

>> 

>> Things have come a ways since!

>> 

>> Dan

>> 

>> 

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>> 

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