True Story No33


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!

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