[R-390] BFO Question

[Roger Ruszkowski]

Chuck,

The BFO PTO just is.
It has a range more than ample so you just crank the shaft on the can to 455Khz.
Back in 54 prior to the invention of counters, you just zeroed it against the incoming 455
being passed through the 455Khz crystal in the 0.1 bandwidth.

You watched the line meter drop to zero and stop ticking.

On a good day you had a signal generator (AN/URM 25) to work against.
Not so good days you used Arm Forces Radio as a strong signal.

You can put a frequency counter on the BFO and set it to 455,000 if you have a counter in house.
Put a tube extender under the BFO tube. Use a blocking cap between the Tube plate and the
counter and you can set the BFO to exact.

In 74 75 in Okinawa we took to setting the BFO with a counter and then zeroed every thing else
including the AN/URM 25 against the BFO at Zero 455Khz.

We also hung the counter on the AN/URM 25 to get 455 for the IF deck alignment.

As tools and test equipment come along and improved we used them.

If the knob does not twist + - 3 from stop to stop smoothly you may want to pull the IF
deck and check the bellows coupler or the shaft bushings on the front panel or If deck front.

If the bellows coupler is not set right you can over stretch it or compress it as you get to the
end of the shaft rotation travel. This is your clue that some adjustment could be in order.
Stretch and compress are not equal so a nice operating  center that gives smooth shaft rotation 
may not be with the bellows coupler at neutral length (set screws loose on one end) and the
BFO at exactly 455Khz. Its a touchy feel thing a point of pride to have a smooth BFO shaft.

Your micro dial should run as smooth as a plain knob from - + 3. But your micro dial has
no stop and you can run the BFO until you hit the bellows coupler starch or compression limit.
The shaft rotation range of the BFO PTO is larger than the bellows range. So
most times the bellows keeps you from cranking the BFO PTO can  into the trash.

But be mindful do not force the BFO PTO. A smooth operation lets you know when you have
 bumped up to the limit and there is not need to force the mechanics of the BFO.

Roger AI4NI