By Andrew Westcott 'M0WAN'
Introduction To Amateur Radio
Contact And Location Info
80m Antenna On A Postage Stamp
40 & 80m combined inverted V
Receiving VLF Signals
• PLT Interference •
Capacitive Reactance Calculator (opens in new window)
Inductive Reactance Calculator (opens in new window)
In recent years a type of device has appeared on the market intended to aid networking between computers without the need for wi-fi or networking cables. These devices are generally known by their abbreviated name of PLT or PLA, or as the 'homeplug'. PLT stands for either 'power line telecommunications' or 'power line technology'. The abbreviation PLA is also sometimes used, meaning 'power line adapter'.
These power line networking devices are supposed to make home networking a simple system suitable for the general public to install. Two units are used, plugged into suitably placed mains sockets within the house. One computer connects to one, the other computer connects to the other and a network connection is established between the two, using the mains wiring as the data transfer medium. No need for untidy cables and having to put up with wi-fi dropouts. The system seems almost too good to be true, surely there has to be a drawback?
Yes there is, one heck of a drawback.
PLT devices operate by injecting radio frequency energy onto the mains wiring within your house and detecting the same as sent by the other unit. The average occupier would be completely unaware of the huge sphere of interference being generated around his home which, depending on the individual topography of the house wiring, could extend for many hundreds of metres around the property.
Although the majority of occupiers would remain unaware of this, this interference has been shown to cause a lowering of broadband connection speeds and interference to DAB radio. The biggest losers though are those who enjoy listening to stations on the shortwave bands, as most of the emissions are within this unique part of the radio spectrum. The shortwave bands are unique because only these frequencies can be refracted by the ionosphere, allowing long distance intercontinental communications to be established.
Someone living near a PLT installation will find that he is no longer able to receive shortwave broadcasts due to the high level of interference generated, and if he is a licensed radio amateur he will find that his receiver has been flooded with the characteristic screech of PLT, rendering his radio station all but completely useless.
Below is a link to a recording of the interference I was getting to illustrate how disabling it is, and how nothing except the most powerful stations can be expected to be heard through it. The noise was present at a very high signal strength throughout the entire shortwave bands and all that could be heard anywhere was this noise - it didn't occur at spot frequencies, it was everywhere.
PLT Interference Recording
After a complaint was lodged with the Office of Communications (OFCOM), a field engineer identified the offending property and the networking devices ordered to be switched off.
Although my particular case ended satisfactorily, Ofcom are now shying away from dealing with similar cases and power line networking devices continue to flood the market unabated. Something has to be done, but due to the sheer numbers of devices Ofcom have allowed to be sold in the UK it is going to be a major uphill struggle just to get the government to accept that there is a problem.
I don't want to load anyone down with regulatory legislation, but there is such a thing as the EMC Directive's "Essential Requirement". Part of this legislation is copied below:
"Equipment shall be so designed and manufactured,
having regard to the state of the art, as to ensure that:
(a) the electromagnetic disturbance generated does not exceed the level
above which radio and telecommunications equipment
or other equipment cannot operate as intended;
(b) it has a level of immunity to the electromagnetic disturbance
to be expected in its intended use which allows it to operate
without unacceptable degradation of its intended use."
Clause (a) is obviously the one to watch here, as PLT devices quite evidently don't allow radio equipment to operate as intended. So why does our quango Ofcom continue to allow this junk to proliferate on the UK market without being challenged?
No, I don't know the answer either.
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© Andrew Westcott 2003 - 2021