"Willey" wrote...

" Peter" wrote...

1. It is not for those using FM CB
FM CB requires more bandwidth than AM. Using speech
processors on FM CB only distorts and knocks out other
channels.

Wrong, what an idiot, using compression does not increase
deviation on FM an modulation

The whole point of the speech processor is to increase the
average modulation (or deviation with FM).
You really need to read up on the subject, consider ALL the
facts...

First of all, consider the UK FM CB legal limits:
RF power output: 4 Watts.
Deviation ("27/81" standard): 2.5KHz.
Deviation (new sets): 2KHz.
Audio bandwidth: 3KHz
Adjacent channel power: 20 microwatts.

You will find that, at 2KHz deviation, the bandwidth of the
transmitted signal goes into the adjacent channel bandwidth.
But this is only on the peaks, which should be only a small part
of the overall signal.
As long as any encroachment on adjacent channels is only on
the peaks, with the average being kept low, users will not
notice it.

A speech processor will increase the average deviation, increasing
the average adjacent channel power. This can cause serious
adjacent channel problems, and take the radio outside of that
20 microWatt limit.
Here in the UK, we have had over 25 years of FM CB and plenty
of distortion and splatter caused by speech processors and
power microphones.

There are also cases where adding a processor makes no
perceived improvement to the audio at the other end, but it sure
as hell starts wiping out adjacent channels. There are some
UK FM CBs which will not sound loud no matter how much
you boost or compress the audio. Some can wipe out two
channels each way, and still sound quiet.

People who have been sold a processor as a cure to these issues,
without anyone looking at why the radio *sounds* quiet, have
been very disappointed when they still had "quiet" audio, but
now a lighter wallet.
But the problem could have been fixed for pennies, without
increasing or compressing the audio.


limiter limits

You have to consider that the processor has no concept
of what 100% modulation or 2KHz deviation are. The exact
level will depend totally upon what the user sets it at inside
the radio. Unless they have the (properly calibrated) equipment
and the knowledge, then that limit could be be overmodulating
or overdeviating.

the Audio MAX.

My power supply is 7Amp maximum, should I run it at that
constantly? How about my CB, which takes 1.6 Amp, should
I use a 1.6A fuse?
Of course not; maximum is exactly that, maximum at peaks.


Fitting an FM CB signal within the 10KHz spacing of CB only
works with a low peak AND average. Increase the average
deviation, and all bets are off.

The changes in our CB standards were made after years of trouble.
Every second channel was unusable, we were down to a maximum
of 20 usable channels.
So the standards were changed; maximum deviation was reduced,
average adjacent channel power was stated and receiver adjacent
channel rejection was set at 60dB minimum.
And, just to make sure, UK CBs had to be submitted for testing
before they could be offered for sale (manufacturers were
no longer trusted).


3. It is not for use in UK CB radios.
UK CB rules state a maximum average deviation. As a
processor raises the average deviation, it can make a
UK CB illegal to own or use.
(RoHS rules also make it illegal in UK).

Again a compressor does not change the deviation, the limiter or
clipper in the radio prevents the over deviation.

The UK FM legal requirements set maximum peak and average figures.
BOTH requirements must be met, or the radio no longer conforms
to the required specification.
Increasing the AVERAGE deviation may take the radio beyond the
legal requirements for use within the Citizens' Band. This makes
the radio open to seizure, and the user open to prosecution.
If people want to risk losing their equipment and getting an
on-the-spot fine (as the DTI have decided should now be done),
that is their choice. But they should at least be aware of the facts.


Regards,
Peter.