THE CHELMSFORD WIRELESS SOCIETY

Primer: Wireless was not invented - it was discovered at the end of the 19th Century by several groups of scientists in different parts of the world around the same time - but first developed into a practical "applied" product most famously, by Guglielmo Marconi at factories in and around Chelmsford, Essex.

And now "Wireless" is everywhere in modern life, you literally cannot avoid it. Unless you live in a lead-lined room (or subscribe to the EE cellphone network in parts of Little Baddow) wireless will find you. Over the last century it has evolved from replacing telegraph wires as a means of sending point-to-point messages, to delivering entertainment, and in the last 50 years it has become the fundamental means of personal communication with cellphones - for the entire planet. It is also widely used in products that we take for granted that have become fundamental to living - such as car and home alarms. And Microwave cookers.

But the range of frequencies available for use by wireless devices is finite, and there is a struggle developing to avoid interference between different types of devices that want their share of radio spectrum.

Wireless is fundamental science - it is the "bottom" (low frequency) end of the light spectrum that you cannot see. Unlike light, some radio waves - depending on frequency - can pass through and around solid objects; although all electromagnetic radiation can be stopped (screened) by enough of a dense conducting substance like lead.

The wireless spectrum is partitioned into groups or "ranges" of frequencies that have different characteristics that have been adapted for quite different purposes, and these groups became described as "bands".

In entertainment applications, most of us will have heard of these ranges referred to as "the medium wave band (MW)", "the short wave band (SW) or high frequency (HF)", "the (very high frequency) VHFband". the VHF broadcast band is referred as FM - which refers to frequency modulation -the method by which information is "applied" to the wireless signal.

Different frequencies go from transmitter to receiver - ("propagate") -  in different ways. Some frequencies in the range 10kHz to 100MHz are suitable for communication around the entire planet. These obviously cannot go in straight lines - but are bent and bounced around the earth's curvature in close association with the way the sun affects the upper atmosphere through the process of ionisation, Since the earth's exposure to the sun is constantly changing, the the skill of early wireless pioneers was to find out - by observation and practical experiment - which frequency ranges worked best at what time of day and year for covering which routes.

Shortwave broadcasting remains the only way to reach audiences around the entire planet using 10 transistor portable radios to receive signals from a 500 transmitter. Keep that in mind when poorly informed politicians enthuse about shutting down all analogue broadcasting and replacing it with digital services that cost 1000 times as much to deploy  and 5-10 times a much to receive - over MUCH shorter distances. The range of Digital Audio Broadcasting (DAB) is 10-30 miles. The downside of this ability is that a SW transmission from anywhere on the planet can interfere with another transmission - on the same frequency - anywhere else on the planet, given favourable "propagation conditions". The orderly allocation and management of these frequencies has been fundamental to all radio and broadcasting from the beginning.

It's coordinated by the ITU (International Telecommunication Union), that also ensures that anyone licensed to transmit in these frequency ranges is suitably qualified to understand all the issues, and the potential that exists for causing interference to other legitimate uses.

Since the arrival of satellite broadcasting in the 70s, "point to point" communication circuits and broadcasting have been supplemented by using geostationary satellites which use ultra high frequencies that travel in straight and contained "beams" that are virtually line of sight. The signals obviously have to travel through clouds and other atmospheric conditions (within limits) but range can be crucially affected by these conditions .

The Chelmsford Wireless Society proposes to provide a versatile forum for all those businesses and individuals around Essex that are interested professionally or personally in wireless in all its forms, and tap into the considerable amount of expertise that still exists here, despite the demise of the original Marconi companies.

 

 

Guglielmo Marconi

 

www.essex.net

work in progress

USP Networks: www.usp.net