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M0WYM

The End of Short Waves?




The end of Shortwaves? Not really - given the nature of physics the Short Wave radio band will always be part of the electromagnetic spectrum! The dilemma that we confront is whether those short waves will continue to be a usable form of communication or will we sacrifice them in order to have cheap and easy methods of linking electronic gadgets together.

What do we mean by 'Short Wave'? Roughly speaking the Short Wave part of the radio spectrum extends from 2MHz to 30MHz and is divided into various 'bands' that are used used for different purposes such as broadcasting, marine, aeronautical, amateur, citizens bands, radio control and numerous utilities. (See here.) Radio, in general can be extremely diverse, and can be accessed from a range of devices - from the mobile phone handsets you might see online at places such as the O2.co.uk website, to industrial transmitters used to send and receive instructional information. Given it's many uses, it is hard to imagine how this form of communication might be altered in the future.

The great thing about the Short waves is that they can be used to send all sorts of signal over vast distances and at relatively low cost. Some transmitters use very high power (500,000 watts) whilst others may use only a few watts but all transmissions are subject to interference at the receiving end. Radio reception is subject to two types of interference, natural and man-made, these are known in radio circles as QRN (Natural) and QRM (Man-made). Natural electrical noise includes static electricity, lightning and noise from space.

spark Man-made interference can be caused any electrical device that has moving parts and nearly all electronic equipment, especially digital devices. By good design most electrical and electronic equipment can be prevented from radiating interfering signals but there are some devices that by their very design will inevitably cause interference. Some instances of this are very strong transmitters nearby, consumer electronics with plastic cases (modems, monitors, etc), some plug-in power supplies (wall-warts). These latter instances are usually the result of bad design rather than of principle.

But there is at least one application of technology that, thanks to it's basic specification, is designed in such a way that it will transmit over large sections of the Short Wave band. Now if you wanted to ensure that water coming into people's homes was clean would you arrange to inject mud into the pipes? Of course not, you would assume that anyone doing such a thing was crazy - insane! That is a fair analogy of a technology that pipes data around the home by injecting it into the mains wiring. Now when you connect a transmitter to a wire you have a system that will radiate, radio waves do not think 'Oh mains cable, mustn't radiate.', a wire is an antenna, end of story - just what a transmitter needs!

This technology comes in two forms, one that carries data over the electrical mains system to the home and the other that carries data over the home wiring from socket to socket where plugin units deliver the data devices such as modems, computers, TVs, internet radio, etc. The former system is known as Broadband over Power Line (BPL) see here. Watch the video below to see how this effects radio communication:



The second form is known as a Power Line Adapter (PLA) and typically plugs into a 13 amp socket and has an outlet for connecting to a computer, etc, via a network cable. It is this type that is becoming popular in the UK, they are sold by all the major domestic computing stores as well as such stores as Argos and John Lewis. The major manufacturers of networking equipment all produce a version of this type of device, see here for an example. These devices radiate over most of the Short Wave band making the reception of normal radio signals impossible, the only exception is that 'notches' have been programmed into the adapters that cut down the interference on the radio amateur bands. This is all very well but many people, for personal and professional reasons, wish to listen to signals outside the amateur bands.

BT Vision are currently supplying Comtrend PLA devices as part of their solution to streaming video around the home. These devices are causing serious interference problems for users of the Short Wave band. The video below gives an idea of how bad this problem is.



Pretty conclusive! So what can be done about this sorry state of affairs? Well, the Radio Society of Great Britain represent licenced radio amateurs in the UK, they have a very expert EMC Committee and do compaign on these issues at national and international levels. Sadly, they are not mandated to represent all non-professional users of the Short Wave band. Currently the International Shortwave League do not appear to be interested in this issue - this seems ridiculous to me and we can but hope things change!

The most active group is UKQRM Yahoo Group (see left for useful links) so if this issue concerns you please do join. If you are suffering from PLA interference (you will need to ensure that it is actually from PLA devices) then report the problem to BT and to Ofcom, you will get lots of help and advice from the UKQRM Group.

Ofcom are investigating a number of complaints, their investigating officers are making site visits and taking complaints very seriously as they have a legal obligation to ensure that equipment does not interfere with the normal reception of radio broadcast. BT also seem to realize that they have a problem on their hands and, in at least one case, are replacing PLA devices with other technology.

Things you can do: Join UKQRM, write to your MP, MEP, contact your local press, write letters to your favourite technical magazine. Have I already mentioned joining UKQRM!

I personally see this in the context of a number of onslaughts on short wave operation these include, cheap unfiltered computer power supplies that carry the CE mark and are now flooding the Uk, badly filtered switch mode powersupplies in TVs & set-top boxes, ditto running modems, chargers,light dimmers, etc. The issue of Power Line Adapters really is a wake-up call, unless we push for improved standards and best practice we will lose the short waves - they will be sunk under an ever increasing tide of QRM.

Charles Ivermee, August 2008.
Please free to copy and use the material on this page, a credit or link back is always appreciated!



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