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SSB CB no thankyou !

Dear Reader,

It has come to my attention that the citizen band community include some persons who are pressing for a relaxation of the rules in Europe. They want CBers to be allowed to use SSB with peak envelope powers of over ten watts. (http://www.ecbf.eu/20yearsECBF.html) also see (http://www.erodocdb.dk/Docs/doc98/official/pdf/ECCDEC1103.PDF)

Now what I am about to write might make me seem like a kill joy or a meanie, please no hate mail as what I am about to write is for the benefit of CBers. Sometimes the greatest favour you can do
someone is to say “no” when they ask for something.

I hold the view that the typically CBer will not benefit from SSB being allowed on 27 MHz, if anything it will handicap them.

If a person wants to use SSB and other exotic modes then I suggest that they undertake some technical training and then get a radio ham’s license. During the training which is the preparation
for getting a radio ham’s license it is hoped that a person will learn the things which they need to know to be able to use SSB (and other radio techniques and modes) in a responsible and legal manner.

I see four main EMC problems existing with radio transmitters.

  1. Breakthrough to non-radio equipment, such as stereos (the speaker leads make a wonderful dipole thus allowing RF energy into the audio amplifier).
  2. Harmonics, either radiated by the transmitter or generated outside the transmitter by non-linear objects being exposed to intense RF fields (e.g. the harmonics formed in a typical AM TV which has a strong 14 MHz (or 27 MHz) current flowing through the set between the aerial connection and a RF ground (or the main’s lead)
  1. Direct reproduction of RF within electronic equipment, for example 10 MHz could enter a 10.7 MHz IF stage and blot out the wanted signal in a FM receiver.
  1. In band problems, for example over-wide signals preventing others from going about their business.

SSB and AM are always worse for point one; any form of amplitude modulation will always make the breakthrough more noticeable. So for that reason I would suggest that AM / SSB with untrained persons are a recipe for trouble.

With FM equipment if a person over modulates it is possible to cause in band interference, thankfully the over modulation should be very clear to the other person who is trying to have
conversation with the over modulator, but a short distance away in frequency the amount of spectral power density should be low.

Also another advantage of FM equipment is that class C (very non linear) power amplifiers can be used.

However SSB is not so forgiving, to build a SSB transmitter you need to generate the SSB signal at a very low power. This signal is then amplified in linear stages to the final power output. If any of
these “linear” stages are poorly adjusted or over driven then they stop being linear and start to generate a lot of in band spurious emissions (splatter).

I worry that some CBers are likely to open their rigs up and fiddle with the output stages to try to get more power at the expense of cleanness of their signal. While it is quite easy to fiddle with a
FM rig to increase the power output and still have a cleanish rig, for a SSB rig it is not so easy. A radio ham who is commissioning a valved amplifier should do things such as check that the valves are not being used outside their ratings.

He or she should try the test of checking that the output power is proportional to the input power, this can be done with the X-Y mode of an oscilloscope. Also using an adsorption wavemeter the ham should check for harmonic production.

The new amplifier should be checked that it is stable, one method is to apply the heater current to the valves, the plate (anode) voltage and all the bias voltages to the grids (screens and control
grids) but no drive to the amplifier, if any RF power comes out of the amplifier then it is too unstable for use.

Another method is to use a torch bulb wired to a loop of wire on the end of a plastic stick, this can be used to check a live amplifier for oscillation. I am not giving all the details of how I would
check a new amplifier intended for SSB service but I think I am starting to give you a flavour of what I would be doing with it.

I think that CB got it wrong from day one, it should have been at about 49 MHz with FM and about four watts of RF. This would have been better than 27 MHz for several reasons.


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