"Allen McBroom" wrote in message
. 97.132...
I'm using a Hallicrafters S-108 receiver, and having a terrible
time
figuring out which (even approximate) frequency I'm listening to.
If anyone here is familiar with tuning old Hallicrafters, I would
appreciate a note of contact.
Thanks.


The SW bands are most easily tuned using the bandspread. Unfortunately
for the SWL, most radios back then only had the bandspread calibrated
for the ham bands. SWLs got a 0 to 100 logging scale. The logging
scale should usually be set to 0 for normal tuning. Or maybe 100.
Which ever gives correct tuning on the main dial. The ham bands were
usually marked off at something like 20 to 50kc intervals. There should
be a dot on the main tuning dial to indicate the approximate correct
position for the correct bandspread use on the ham bands.

Probably the most common way to use the bandspread was to tune in a
strong SW signal at a known frequency and tune down from there using the
bandspread. Say the bandspread was set to zero at at a known
transmiission at 9760kc. Another known signal at 9580 kc might turn up
when the bandspread indicator gets to 18. That's a 180 kc difference
for every 18 bandspread divisions. Or something like 10 kc for every
division. The breakdown probably isn't linear, so smaller differences
in frequency will give better results. And the breakdown won't often
come in with round numbers. I'm sure it kept the sliderules and scratch
pads busy back in the olden days.

A crystal calibrator could be used to give regular dependable signals
across the bands. 100 kc was a common crystal calibrator frequency.
That makes the math easier. The more expensive radios of that era had
internal crystal calibrators.

A SWL could keep all this info in a notebook and do the hard work only
once.

The analog radio's local oscillator can be heard with with a digital
radio. The local oscillator will usually be 455 kc above the received
signal. Sometimes the LO is 455 kc below the signal, usually on the top
band. Using a digital radio in this way might sound silly, but even a
very cheap digital can give a very precise readout to a better quality
analog readout radio.

There's now a digital readout which can be added to an old radio:

http://www.aade.com/#dfd

Do you have the Hallicrafters manual for your radio? There's probably
one at the BoatAnchor Manual Archive.

Frank Dresser