From: peterk@seanews.akita.com (Peter A. Klein)
Subject: Tuning SSB using an adjustable BFO
Organization: SEANEWS - Seattle Public Access News + Mail
Date: Tue, 15 Dec 1992 19:52:54 GMT

Emailed this to an as-radfo in Bristol, UK. It bounced, so I'm posting it 
instead. Hope it helps someone.


The basic idea is to offset your BFO about 1.5 kHz from center, and then
tune in the signal until the pitch sounds right. You set the BFO on one
side for USB and the other side for LSB.  For protables with only .1 kHz
resolution in the main dial, you will have to make a couple of marks on
your BFO dial for the approximate USB and LSB points, tune it as close
as possible with the main dial, and then tweak the BFO to get it just
right.
 
For USB, you tune your BFO below the "center" and tune your main dial
the same amount of offset above the actual suppressed carrier frequency.
For LSB, it's the reverse--you turn the BFO above center and the main
tune below. So you see, SSB means setting the BFO an main tune dials
"wrong," but each in the opposite direction! Your BFO may be calibrated
+ or -, but who knows if this refers to the actual frequency of the BFO
or the signal it's going to receive?
 
To calibrate the BFO, you can use a known USB and LSB signal.
Alternately adjust the BFO and main dial until you find a spot that
reproduces the voice best, and mark that spot with a colored pencil,
piece of tape, etc. It the BFO is tuned too far off center, only the
"highs" will be reproduced, and the voice will sound tinny, even though
you have the signal tuned in right. If the BFO is too close to center,
the signal will sound bassy.  As for known USB and LSB signals, use the
ham bands. Ham voice signals around 3.7 or 3.8 - 4.0 Mhz ( I forget the
UK allocations for voice, but you should find something in that general
area, especially at night) and about 7.050-7.1 mHz are LSB.  Signals in
the 14.1 - 14.35 and 21.2 - 21.45 range are USB.
 
To get an approximate idea of where to initially set your BFO, tune in
an regular AM station that is doing only voice, not music. Now turn on
your BFO. Tune the main dial to the exact frequency (a plain old MW
broadcast station is best, since you can look up the frequency in your
local paper).  Now rock the BFO back and forth. You'll find a center
point where there is no tone, with a tone of rising pitch being
generated as you move the BFO to either side of this point. Mark the
center point. Now turn the BFO dial in either direction until you get a
tone of about E-fla E-flat two octaves and a third above middle C on the
piano. If I remember my acoustics right, that is about 1.5 kHz. Mark the
spot. Now move the BFO to the other side of center, generate the same
pitch, and mark the spot again.
 
So you see, you can find the spot by trial and error, or by getting it
about right and then using trial and error to get it right on.  But once
you've found the spot, you mark it, and the rest is easy.
 
Tuning SSB does take practice. Once you get it "in your ear," thought,
ti will become second nature. Having a a main dial with a resolution of
only 0.1 kHz means that you will often have to tweak the BFO slightly to
get it exactly right, but this is no big deal once you know how.
 
Once you've found your BFO points, you can practice by tuning any AM 
signal as an SSB signal. And guess what--doing that is the manual 
equivalent of the expensive "synchronous" tuning feature found on the 
Sony 2010, etc. If there is interference on one side of a SW broadcast 
station, you can reduce or eliminate it by tuning the desired station as 
an SSB signal, using the side band that is on the opposite side of the 
signal from the interference. I've been doing it for years.  It also 
helps reduce selective fading distortion in some cases.
 
Hope this helps, best to you-- Peter Klein, KD7MW

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