Everybody (except Collins receiver owners) used to have a crystal
calibrator, a little black metal box with a vacuum tube on top,
that put out a signal every 100 kHz (100 kc in those days). You'd
set the bandspread to 0 and tune the main tuning until your 100 kHz
signal was heard, the idea being that the main tuning was accurate
enough to distinguish 100 kHz frequencies so you got the right one.

Then tune with the bandspread and take the frequencies off it as
offsets from the main tuning frequencies. That is, the bandspread
does the part below 100 kHz and the main tuning does the part above
100 kHz, in the constructed frequency.

You'd either leave the receiver on, or recalibrate as it drifted,
as you use it.

If you know a station's frequency, you set the bandspread to the
100 kHz part and tune the main tuning to hear the station, and then
that calibrates the receiver instead of the crystal calibrator.

Basically listening was partly calibrating the receiver and partly
tuning for stations, if you were interested in what frequency you
were hearing.

--
Ron Hardin


On the internet, nobody knows you're a jerk.