MrRas wrote:

I have an Eton E5 SW radio, I love listening to broadcasts from all over
the world, but I've had this radio for a few years now... and there is
one problem. I still have no clue how to work the SSB function.

First of all you have to understand what SSB is. A normal AM signal consists
of three things. The first is a carrier signal which is always on, the other
two are the information you want to hear, which are called sidebands.

Since the sidebands are what you need, you can remove the carrier entirely
and still have a useable signal. That's where DSB or DSRC (double sideband
reduced carrier) signals come from. They can be received as an AM signal
by an AM receiver with far less power used by the transmitter.

Now what would happen if you only transmitted the information you needed
to make up the full signal? It so happens that both sidebands are the
same, being mirror images of each other.

So one can transmit the same INFORMATION, using a lot less power by
transmitting only one of the sidebands. The problem is that without a
carrier, or both sidebands a regular AM receiver can not decode the
information.

The question is how do you get it back?

Normally this is done by mixing a new carrier with the signal, and
stripping out what you don't want. There are various methods for doing
this, but they all rely on the frequencies matching. On an SSB signal if
the frequencies match exactly, the sound seems "normal" if they are too
high or low or vary, the signal gets that funny distortion that sounds
like the rebel pilots in the final attack on the death star in Star Wars.

Now here comes the problem with SSB and shortwave listening. If you use
SSB to receive an AM signal, and the carrier frequencies don't exactly match,
or are not stable, you get a howl. The howl is the mixing product of the two
mismatched signals.

If you tune them to the point that they match exactly, that's where the
magic happens. As a shortwave signal fades in an out, the reception of it
gets better and worse. If you mix a carrier with the fading carrier and replace
it, the information you want is still received and the fading dissapears.

This is called ECSS. In order to work, it requires a frequency stable
transmitter and receiver and exact tuning.

If you don't have the exact tuning you need, or a stable enough receiver,
then it won't work and will howl. Therefore not many people use SSB
receivers for AM reception.

If you want to receive SSB signals, there are occasionaly a few of them
on shortwave broadcasts. It's not that popular because the majority of
shortwave listeners in the world don't have receivers capable of SSB
reception.

You are most likely to hear SSB signals on the ham bands and utility
frequencies. From international aircraft flight controlers to fishing boats
too far off shore for VHF and so on. Most of them are USB (upper side band),
but ham transmissions on the 1.8mHz,3.5mHz and 7.0mHz bands are usually LSB
(lower side band).

Except on the US 5mHz band, where USB is required, hams may use either
USB or LSB, but the convention is LSB below 10mHz.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
To help restaurants, as part of the "stimulus package", everyone must order
dessert. As part of the socialized health plan, you are forbidden to eat it. :-)