OK, CB's now legal but all the Breakers
out there are still breaking the law!
CB Radio was big in the States with
lots of feature films of rebellious lorry divers and the like
glamorising the hobby to the extent that the UK Government of
the day were forced by popular demand to legalise the hobby in
this country.
By that time there were literally millions
of imported sets being operated by otherwise law-abiding citizens,
young and old alike.
Industry in the shape of our own semiconductor
specialists were attempting to capitalise on the soon-to-be booming
market in locally manufactured transceivers, by designing special
devices to enable the new sets to be made….
..once Government gave the go-ahead.
In the US the CB standard was loosely
called "AM".
Strictly speaking sets had moved forward
from basic AM which is designated "A3" to single sideband,
a sub-set of A3.
By removing the carrier and one of the
sidebands a lot more of the transmitted signal was concerned
with intelligence than straight AM.
With AM one first had to develop a thumping
big carrier which, by itself, imparts no intelligence whatsoever
and for the most to be got from AM you needed to develop, not
only the huge wasteful carrier signal, but also a pretty potent
audio signal generating lots and lots of modulating power.
In summary, for a 10 watt signal you
needed to provide something like 40 or 50 watts of DC power in
order to drive the rig.
SSB is much more effective.
Once the designers had sorted out a
cost-effective method of deriving the basic SSB signal most of
the DC power used to drive the set would be converted to intelligence.
Put another way, for the same power
input you could generate masses more signal from SSB.
Anyway the UK Government was now pondering
over the standards to be applied to the soon-to-be legalised
Citizens Band.
Industry was gearing up to chip production
and a million CB'ers were hoping to make the trip to the Post
Office and for a nominal sum become legal.
The announcement was made.
What's FM?
What channels are those?
What's this about fitting attenuators
in the aerial lead?
What height restriction on car aerials?
The Government had got its own back
on the powerful CB lobby!
ALL the illegal CB rigs were now decidedly
illegal.
Most of the CB aerials were decidedly
illegal.
Most car installations, even if they
had been permitted (and they weren't), were illegal anyway because
their aerials were too big!
And of course no-one would hear you
if you transmitted on a now-legal channel as these were totally
different to those used previously!
A new logo was to be carried on the
front of the new rigs certifying that the thing was FM and did
not generate more than the legal amount of power.
Industry was distraught because they
had assumed that the UK would adopt the standard CB channels
and all the new devices designed for the launch were now so much
scrap!
Why FM and why the various restrictions?
Perhaps the huge popularity of the new
hobby had itself been to blame?
In our fairly cramped country, unlike
the rolling prairies of the States, it would be difficult to
squeeze everyone in and maintain a reasonable quality of communication?
FM has a couple of major features useful
in the provision of a relatively high quality communications
hobby.
Firstly, capture effect means that the
strong local signals would totally swamp more distant signals
unlike AM were they all get mixed up together.
Secondly, interference to TV receivers
is minimised because their FM origin has little effect on wide-band
AM video signals.
In order to provide a flat playing field
"ERP" or effective output power was going to be limited.
You could not put your signal head and
shoulders above others by using a high gain aerial because aerial
size was to be governed.
True you could have a big aerial but
you would have to insert an attenuator in the lead to stop you
getting an advantage over your neighbours.
The same went for car installations.
Aerials were restricted to keep your
signals down to a respectable level.
All this was a shock to the CB fraternity,
some of whom ploughed on with their AM equipments but sooner
or later, in order to join in with the rest of the community,
bought an FM rig and went legal.
What about the chip manufacturers?
Well after scrapping the first load
of chips they sorted out new designs and soon FM rigs were commonplace.
I picked up some samples of the old
chips.
Guess what?
By a little ingenuity they were usable
on the 2 meter amateur band.
Whether by design or good luck, I never
found out, Mr.Bryant, the designer in the Company for whom I
used to work, came up with a superb circuit for generating 2
meter signals from the CB chipset.
I'll go into this in another story…try
No.34!
