SR ) writes:
I mostly use my Sony ICF-2010 for swling.

Many times on 75 meters, I hear out of tune signals or voices. So, I
then turn the radio to LSB or USB. And then the audio of my radio goes
down. But the signal strength is still high or strong.

I know their Hams operators talking. But the bigger problem I have is
that when I go LSB or USB to better hear them, I lose almost all of the
audio. Even if I bring the volume all the way up. I don't understand this.

These two paragraphs don't seem to match, but then it's not clear if
you are talking about frequency or volume going down.

I suspect you aren't using the receiver properly. If there's a tuneable
BFO, you may not be getting it to the right spot in relationship to
the IF filter, which will cause it to filter out the incoming signal
if you try to tune for best whatever.

I really don't see the point of side band transmissions, if everyone is
going to have a problem tuning in. -One voice talking too high and the
other is too low. Maybe their is something more to this. I don't get it.

It's more efficient. A regular AM signal has two sidebands, both
mirror images of the other, and a carrier. The actual information
can be transmitted in one sideband, so the bandwidth is halved. The
carrier serves no purpose other than to demodulate the signal at
the receiver, yet it requires power. If you only send one sideband,
all the transmitter power goes to it, rather than it being split
between the two sidebands and the carrier.

When you don't transmit the carrier, you need to generate a synthetic
carrier at the receiver end, ie the BFO. This does the same thing
that the carrier does, only locally to the receiver, beating the sidebands
down to audio.

If you only send one sideband, then there's no way of knowing exactly
where the locally generated "carrier" should be. Hence it can sound
funny, as you will notice something mistuned by even a few hundred
Hertz.


Now what's funny is, on my Cobra 148-GTL, when I turn to LSB or USB, the
signal gets a lot stronger. Where as with my Sony ICF-2010 it's the
opposite.

A CB set is crystal controlled, so "tuning" is out of your hands.
Not only is the tuning to the channel crystal controlled (or these
days derived from a crystal reference), but the BFO is crystal controlled.

Turn the channel selector to the desired channel, and you know it is
tuned right where it should be (and so will the transmitter on the other
end). But there will be a good IF filter in there with sharp
sides, and the BFO will be set to right where it should.

A shortwave receiver, well first you have the main tuning and you
need to tune that so the incoming signal will be in the passband
of the filter. Mistune that and some of the incoming signal
will not be in the passband. Then if the BFO is tuneable, you
need to decide where it should be tuned to. Leave the BFO fixed,
and tune the sideband signal, and you will hear the voice move
in frequency as you tune across the band. The incoming signal
is varying in reference to the BFO. But it will also
vary in amplitude, because when you tune off the center frequency it
will be on the slope of the filter and attenuation of the filter comes
into play.

But keep the receiver tuning fixed, andtune the BFO, and you will likewise
hear the voice move in pitch, since you are varying the BFO in reference
to the incoming signal. When the BFO is tuneable, you have two variables
rather than one.

On those cheap receivers, the BFO is often treated like a fine tuning
control, but when you use it that way you are moving the BFO in
reference to the IF filter. Hence you can end up with a combination
where the desired signal is not properly in the passband of the filter,
even if you have the pitch right.

In the old days, tuneable BFOs would have some sort of rough calibration,
and you'd basically set it so it was in the right place along the
receiver passband, and not tune it except to switch to the other
sideband.

Also my sony has a Sync button, when I press that, the audio gets low
too as well. Why?

A synchronous detector is for when there are two sidebands being
transmitted, either with or without a carrier. It's the same
basic premise as for sideband, ie a locally generated carrier.
For a signal where the carrier is sent, this helps because if
the carrier fades in the wrong way, you can't demodulate the
sidebands where the information is. (And there can be cases
where the transmitter does not send the carrier, to save
transmitter power and so there are no beat notes between
adjacent channel transmitters, so the carrier has to
be locally generated.) But since in this case there are
still the two sidebands, if you don't have the BFO right between
them, not only will you have odd pitched voices, but the two
sidebands will not translate down to the same frequencies at
audio. A 1KHz tone in the sideband will translate down to 1KHz
on an AM receiver, or a receiver with the BFO properly located
right between the sidebands. But if that BFO is mistuned,
one sideband will translate down to 990Hz, and the other to
1100Hz, so for every audio frequency at the transmitter there
are now two in the receiver, and it's impossible to listen to.

The synchronous detector adds circuitry to automatically tune
the BFO to right between the sidebands, so everything will work
properly.

(But it won't work on single sideband since there's not enough
information, ie the spare sideband, to indicate where the BFO
should be tuned.)

Another thing that I notice in other radios: Their is no LSB or USB just
SSB. I do not understand how that works or which is greater to have.

Likely because it's got a tuneable BFO, or it's fixed tuned right
in the middle of the IF filter. The reason there would be two positions
is that it puts the BFO where it should go for both Upper and Lower
sideband. If it's not selectable, you have to fuss yourself.

Also, in my Panasonic RF-2200, their is a BFO button. It seems to work
for turning up Ham operators and CW signals. -Although you have to tune
a bit up or down. (I love the sounds of radio squeals). But when I pick
up a regular SW broadcast, I see no other use for the BFO button.

That's because it only serves the purpose of replacing the
carrier that wasn't sent, or to beat the incoming carrier of the CW
signal down to audio. A regular AM signal has the carrier, so
it doens't need it generated locally.

I would like to know: When, how and why did SSB and BFO came about?

Sometime in the 1920's the theory was figured out. The telephone
company used that theory to multiplex phone calls on underwater cables.
There had to be some commercial use of SSB on radio in the thirties,
given that there were a few hams who tried it out then. But it
didn't start becoming common till after WWII, when more stable
and selective receivers were more common (thanks in part to WWII
surplus, and also the prosperity that the war brought). It became
much more common in the late fifties into the sixties in amateur
radio circles, and by the late sixties AM was fading.

The various armed forces have used SSB from the fifties, and some
point to point work used it. Note that it's not common in two way
communication, and of course has only been used sparsely for
shortwave broadcast.

Michael