[time-nuts] Vintage Frequency Measurement
Bill Byrom
time at radio.sent.com
Mon Feb 13 04:02:58 UTC 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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