7
FM Narrow band frequency modulation (max. 2.0 kHz range)
USB Single-sideband modulation, upper side band
LSB Single-sideband modulation, lower side band
The different modes for CB radios are partly historical, as CB radio exists since the 1950s. AM (amplitude
modulation) mode corresponds with the technical operation of medium wave and short wave broadcast und is,
except for CB radio, currently used for aircraft radio. While speaking the transmission power is adjusted
rhythmically (technical term “modulated”). AM is traditionally the radio system used by truck drivers worldwide for
CB radio. The low background noise is advantageous if for instance in low interfering diesel trucks squelch is left
open during standby operation. A disadvantage is the lower communication range compared to FM (because of
higher allowed power in FM) or even SSB and the varying volume between near and far stations.
In FM mode the transmission power is always the same when speaking, thus hardly any interferences from other
units are to be expected in this mode. Instead the frequency of the unit varies during speaking and for this reason it
is called frequency modulation. Due to the interferences expected for AM and SSB some countries only permit FM.
Advantage is a greater range compared to AM and a constant volume of near and far stations as well as a clear
modulation sound. Some noise is a disadvantage and can be heard with weak or missing signals. In FM mode it is
basically not possible to leave squelch open in standby operation.
SSB (Single-SideBand) marks the height in the development in long distance traffic voice transmission. SSB mode
avoids the disadvantage of low range of AM and concentrates all transmission power on a minimum frequency
width with speech pauses reducing the output to nearly zero. For reception a special circuit ensures that the
transmission of cut off “sidebands” and the “carrier” are again restored. This achieves an enormous increase in
range compared to AM and FM. Not only does the transmitter reach further, also the receiver is substantially more
sensitive through the halved bandwidth. All this has to be paid for with the disadvantage of a very fine tuning being
necessary for reception and that there is a higher risk of interferences of nearby devices during transmission. Due
to the necessary fine tuning of the receiver with the “
Clarifier
” (11) the use of SSB in moving vehicles is a problem
and can distract in an objectionable way from the traffic, similar to using a mobile phone. SSB is rather a mode for
base stations. This is also the reason, why today only experienced radio operators use SSB – you really have to
train and develop a sure instinct for the correct setting.
USB and LSB
In SSB mode a conventional channel is divided in two halves: the so-called
upper sideband
(USB) and the
lower
sideband (
LSB
). Both can be used independently. Example: you transmit on channel 9 in USB. In reality you use
for speaking only the frequencies upward of 27.065 to approximately 27.070 MHz, while in LSB mode the
frequencies below 27.065 MHz to approximately 27.060 MHz are used. Both sidebands are mirror-inverted and
this is why receiver and transmitter must be set to the same sideband. Otherwise you only receive some
incomprehensible gibberish.
Set Transmission Power
Your unit comes with continuously variable transmission power. In normal state the control knob
PWR
(14) should
be set fully clockwise. In this setting you achieve 4 Watts in FM and SSB and 1 Watt in AM. Turn counter-clockwise
to reduce power to approx. 100 mW. This should be done if you want to be heard only in the absolute near
proximity.
By the way: it also reduces the general electric smog level if the transmission power is set as low as just needed
for the radio link!
How to Receive SSB?
As receiving station of course you do not know in which sideband your outstation is currently transmitting. That the
outstation is transmitting in SSB mode is easily found out, because the “squawking noise” is very different from FM
or AM signals. First receive in USB. Carefully tune through the
Clarifier
. If you hear a “Mickey Mouse like” pitch
carefully fine-tune to a more comprehensible pitch. If this is not possible try the other sideband
LSB
.
You will need some experience until you clearly understand your first dialog partner in SSB mode. But surely you
will soon be rewarded by your first DX (= long distance traffic) connection.
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