Red Wave Radio

What's 'USB, 'LSB', and 'SSB'?

Quote:>What's 'USB, 'LSB', and 'SSB'?

        1) The original carrier frequency
        2) An upper sideband which varies in amplitude with the sound
        3) A mirror-image lower sideband

Most of the power goes into the original carrier frequency.

If you drop the lower sideband, you get upper sideband.

If you drop the upper sideband, you get lower sideband.

Either of these is Single Sideband.

USUALLY, they also drop the carrier. This is a much more efficient
mode of transmission which gives more punch for the wattage. However,
when you listen to a carrier-supressed signal on a normal AM receiver,
it sounds like Donald Duck. To receive a SSB-carrier-supressed signal,
the receiver has to reinsert its own version of the carrier. Either
the radio has a LSB/USB control, or it has a BFO control which
requires somewhat tricky tuning.

MOST broadcasters are double sideband with carrier. A few broadcasters
have done USB with carrier. A few do USB without carrier.

Most ham radio stations are LSB WITHOUT CARRIER if they are on the 7
MHz band or below and USB otherwise. This has to do with the history
of how hams made SSB. Most non-broadcast/non-ham voice stations on
shortwave do USB without carrier.

Here is a good web reference:

http://www.dxing.com/modesand.htm

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        AM stands for Amplitude Modulation. In AM we take a radio
wave and impose our audio signal onto it so that it's amplitude
(or magitude) will vary in relation to the audio. The radio wave
is called our carrier, since it carries the audio (which we will
call intelligence) from the transmitter to the receiver.

        When we impose (or modulate) the intelligence into the
carrier, something called sidebands form. If we modulate a 1 KHz
signal onto a 1000 KHz signal we will get a lower sideband (LSB)
and an upper sideband (USB). It would look something like this...

                      1000 KHz (carrier)
                        |
                        |
                        |
           999 KHz LSB  |   1001 KHz USB
                    |   |   |
                    |   |   |
         -----------|---|---|----------

        Now keep in mind, 1/2 to 2/3 of the total power in our
signal is in the carrier. The BIG downside of AM is that the
carrier gets "thrown away" after the intelligence is taken off of
it. Only 1/3 to 1/2 of the power is in the sidebands. The
advantage of AM is that it even the most crude radio circuits can
detect it. Simplicity on the receiving end goes a long way
towards keeping AM alive and well.

        DSB is known as double sideband. If we could take the
energy that the carrier uses and put it into the side bands, we
end up with a mode of transmission that is more efficient than AM
because very little of the energy would get wasted. If we took
our 1 KHz test tone and send it DSB on 1000 KHz it would look
something like this....

           999 KHz LSB      1001 KHz USB
                    |       |
                    |       |
                    |       |
                    |       |
         -----------|---|---|----------

        As you can see, 50% of our power goes into the LSB, the
other 50% goes into the USB. While power is used more efficiently,
there is a downside, a regular AM radio cannot receive this kind
of signal since it relies on the carrier to help "detect" or
demodulate the signal. A device like a BFO (Beat Frequency
Oscillator ) is needed to re-insert a new carrier so the signal
can be detected like a regular AM signal. Note too that a DSB
signal is just as wide (IE: takes up as much bandwidth) as an AM
signal.
        We also know that the Upper and Lower Sidebands are
identical, mirror images of each other. You are not going to run
into a DSB signal very often, if at all (I read in an old book
that it was used from time to time on the 1750 metre experimental
Long Wave Band).

        Now there is also a variation on this theme where there
is a carrier, like AM, but the carrier is at a reduced power
level. From what I understand (since I have yet to monitor such a
signal) a AM radio can pick up such a signal, but rather
distorted. I would guess such a signal would be rare on the world
bands

        SSB stands for Single Side Band. Like DSB, we do not use
a carrier. Unlike DSB, we use only _one_ of the sidebands, hence
the name. Since both Upper and Lower sidebands are alike, we can
transmit only one of them and still convey the same information.

        We can use the Upper or Lower sideband, it really does
not matter. Where one is preferred over the other is really more
tradition or convention rather than necessity these days. When we
are sending only the Upper Side Band we just say USB, or with
Lower Side Band, LSB.

        This is a look at a 1 KHz test tone send on 1000 KHz SSB.
Showing what USB and LSB variations look like.

Upper Side Band (USB)

                            1001 KHz USB
                            |
                            |
                            |
                            |
         -----------|---|---|----------

Lower Side Band (LSB)

           999 KHz LSB                  
                    |        
                    |        
                    |        
                    |        
         -----------|---|---|----------

        Notice that not only 100% of the power goes into the
sideband, making it more efficient, but it is only half the width
of a DSB or AM signal ! This means that all else being equal, two
SSB signal can fit where only one AM signal can fit. Since all of
the power is going into one sideband, there is going to be an
effective gain of 9 db (8 times) over an AM signal of the same
strength ! But like the DSB signal, a BFO is needed to re-insert
a carrier so it can be detected like a conventional AM signal.
Amature Radio operators (Hams) and various Utility Stations use
SSB for just these reasons. AM is still more popular than than
SSB on the world bands because many people in poorer countries
own simple receivers with out BFOs. A good example of a SSB on
the world bands is Radio Havana Cuba on 9830 KHz (around 0100-
0300 UTC), USB.

        There is a variation on SSB, which is simply an SSB
signal with a carrier added (or you can think of it as an AM
signal with one of the sidebands trimmed off). While power is
"wasted" with a carrier, the signal is still only half as wide as
a regular AM signal. An easy to find example is CHU, a Canadian
time station at 3330 KHz (and 7335 I think) that uses USB with a
carrier. Here's what it would look like if they sent out a simple
1 KHz tone.

CHU Canada, 3330 KHz

                       3330 KHz
                        |
                        |
                        |   3331 KHz USB
                        |   |
                        |   |
         -----------|---|---|----------

        Since this signal comes with a carrier, a regular AM
radio can receive it just fine.

        CW stands for Continuous wave. Hams and some Utility
stations use CW to send Morse Code by turning the carrier on and
off. The CW signal is just a solitary carrier, with nothing on
it.

A CW signal at 1000 KHz

                     1000 KHz
                        |
                        |
                        |
                        |
                        |
                        |
        ----------------|--------------

        A regular AM radio will not hear the signal, the S meter
will move along with the presence of the signal, the AGC (Auto
Gain Control) line voltage will change with the signal too. You
may hear a change in the noises & static or something similar. To
hear the famous "dit - dah" of CW, you need a BFO. CW signals,
while still numerous, are not as numerous as they once where.
Most services & utility stations will be dropping CW by 1999. Hams
will still be using CW for quite some time.

--
     Member of the Signal Surfer DX Club, check out our web site at:
                    http://www2.awinc.com/users/djabs

SSB -- Single Side Band

Is really suppressed carrier, single side band.

Amplitude modulation is transmitted with a carrier and upper and lower
sidebands. In SSB, no carrier and only one sideband is sent. So -- when
the operator quits talking -- no signal is transmitted. Unlike AM or FM
radio where a carrier is sent irrespective of modulation.

SSB is most commonly used for long distance voice communications by
Amateur Radio Operators. Also used by the Military and some Short Wave
Stations.

Changes strength of signal according to how loud the voice.

Compared to AM == 1/2 of the signal and the carrier is removed allowing
all the power to be concentrated in the other half.

Takes up half the space on the radio bands as A.M. so twice as many
stations can use the same amount of frequencies. More or less.

Sound quality can be poor depending on bandwidth transmitted. Hams use
narrow BW.  Sounds like "Donald Duck" if not tuned properly. Requires
precise tuning.

Requires special radio equipped with a device called a "B.F.O." (Beat
Frequency Oscillator) in order to be received. Or a special detector
circuit i.e, product detector.

-----

USB -- Carrier and lower sideband is suppressed and the upper sideband
transmitted.

LSB -- lower sb sent, Carrier & upper sb is suppressed

Difference between USB and LSB -- none really -- as only one sideband is
required to transmit intellegence, either one will do. Needs "Special"
radio features however.

If you just can't un-donald duck it (tune it in) --- switch side bands.

For Hams (in general) 160,80,40 Meter Bands --- LSB
20, 17, 15, 12, 10M bands --- USB

Regards
Rod in San Diego
--
AC6V's HAM  AND  DX  REFERENCE  GUIDE
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Master Index: http://pw2.netcom.com/~ac6v/pageas.html

***EDITED***

Quote:>and two side bands called USB and LSB.  AM has good fidelity but the
>transmitters power is shared across the carrier and two sidebands.  If you
***EDITED***
>punch  for a given transmitters power level but you loose fidelity.  
>If you listen to Amateur radio use LSB below 10 MHz and USB above 10 MHz.

        The reason that SSB tends to have lower audio quality (fidelity) is
more due to implementation than to anything inherent to the mode itself.
For example, if the transmitter was to drift 250 Hz, the SSB signal would
have to be retuned while the output of the AM receiver would have no real
change in output.

        On the receiving end, a receiver drift of 250 Hz would also make
reception of difficult while on AM it would not be noticed much. Also, some
radios seem to be harder to tune on SSB than others due the way  they are
set up. It is much easier to clean up a signal on my Drake SW8 than a
Grundig YB 400 in part because that thumbwheel on the Grundig is so small.

        Keep in mind too, a lot of SSB users outside of the world bands
tend to use a smaller bandwidth, since they are just sending voice or data.

        A good example of the capability of SSB in terms of fidelity was
when I was listening to Radio Havana Cuba last Sunday. I tuned to their SSB
signal to listen to a music show and it sounded very nice ! But keep in
mind, their transmitter was not drifting that day and I was using a more
expensive receiver.

        Like I said, I think the reduction in fidelity when using SSB is
more a matter of implementation rather than the mode itself.

--
     Member of the Signal Surfer DX Club, check out our web site at:
                    http://www2.awinc.com/users/djabs

--
     Member of the Signal Surfer DX Club, check out our web site at:
                    http://www2.awinc.com/users/djabs

Matt J. McCullar, KJ5BA
Arlington, TX