"james" wrote...

Actually they don't have loads of bandwidth to play
with. In most cases 15KHz

James,

That is AUDIO bandwidth of the input signal, not the
bandwidth allowed for the transmitted radio signal.
For CB, the audio bandwidth is just 3KHz.

I'll bet you would consider that ratio significant if
it was applied to a pay-rise... and I bet you would find a
way to spend 5-times the income :~)
We are greedy creatures. Give us more and we will manage
to use it, wonder how we ever managed, and demand
another increase.

Here in the US they are limited to 75KHz peak
deviation.

Now we are getting closer... that is much better than the
2KHz deviation now allowed for UK FM CB.

Broadcast station deviation is the same here, 75KHz.
With an audio bandwidth of 15KHz, the total bandwidth
required for a basic mono signal of that quality is around
120KHz.

12 CB channels in each direction just to match the quality
of the mono signal.

The CB channels, and the 10KHz spacing, were set back in
the days of AM. But then we in Europe took this spacing
and decided to put an FM signal in there.
It took some squeezing and some careful balancing tricks,
we even had to reduce the deviation from the original
2.5KHz down to 2KHz.


Regards,
Peter.