Ofcom meeting about PLT interference

Hi

Ofcom invited UKQRM to its London office to have a meeting about PLT interference. on the 27/01/2009.

It makes interesting reading.

Its quite long so click on the link below if your interested.

http://mikeandsniffy.co.uk/UKQRM/UKQRM_meets_Ofcom.htm

Cheers

Paul

I realise the subject text is limited but not everyone knows that PLT probably means Power Line Transmitters (or mains networking etc.).

I think that this attack on Power Line communications generally by a small group radio enthusiasts is in my opinion unjustified.

The answer to their problem is very simple. If BT is breaking the law by supplying the Comtrend UPA Adapters then take them to court and leave the rest of us out of it.

Hi

Terry its not just Comtrend adapters. I don`t think its unreasonable for any radio user CB`er, ham, shortwave listener who has been using the shortwave spectrum long before this flawed technology came along to listen in piece.


Cheers

Paul

Are there any Ethernet over mains devices which cause less problems, i.e. perhaps you could steer people towards the units which cause the least interference?

The fundamental problem is that while some units don't transmit data continuously, if they are moving data they then cover most or all of of the 3-30MHz spectrum with data sub-carriers. Even where there are notches for the amateur bands these are not deep enough to be fully effective and amateurs tend to operate with weak signals which means that the interference is more noticeable.

The signal levels used are sufficiently high that tests in accredited test houses show that limits that other devices are expected to comply with are exceeded by about 28dB. If the levels injected were reduced by that much then practically no data rate would be possible as the receivers simply couldn't detect the PLT transmitters in amongst all the mains hash.

If you look at the wiring used, mains tends to have abysmal balance, so that unlike Cat5 UTP the leakage levels are high.

Somehow the PLT industry has managed to get these into the market and has bypassed the need to test to standards like CISPR 22 (EN55022 in Europe) that would have precluded their use at all, forcing designs that don't interfere with anything.

There are between 50 and 60 thousand radio amateurs in the UK, plus other HF radios users. HF radio has been in used for more than 100 years, it is the only long range radio technology that has a global reach.

A difficult problem to solve the desires of both sides of the problem.

Unfortunately, the answer is no. The OFDM modulation scheme that the devices use to gain bandwidth and the frequency range that they use means that they cannot be radio friendly. Products based on the UPA standard (Comtrend etc) obilterate spectrum 24/7, but HPA devices generate noise mainly when transferring data, but still cause noise when dormant although at a lesser level.

Hope this helps

Richard M0SNR

Edited by M0SNR (Fri 30-Jan-09 23:39:31)

"There are between 50 and 60 thousand radio amateurs in the UK"

How many of them are actually active ? I hung on to my licence for about 6 years after I sold all my gear, "just in case". I then realised that there was no way I was ever going to re-join a hobby that was so full of old farts who were stuck in the dark ages, so I stopped paying. I listen to 2m repeaters these days (those that are still on), and they're like ghost towns.

Edited by deleted (Sat 31-Jan-09 10:17:56)

It is not that easy to put a hard figure on the number of UK amateurs active on the HF bands. However I have over 10,000 contacts with UK amateurs in my log. In a typical contest (which in itself involves a small percentage of active amateurs) I maybe work a couple of hundred in a weekend. As a gut feeling there are probably 5000 or so who come on the bands from time to time - and the number has in fact grown in recent years after the removal of the morse requirement. But although amateurs are very concerned about the impact of PLT the number of complaints from them are rather less than from short wave listeners due to the notches which have been added to the devices as a result of discussions with the manufacturers (via national amateur societies). Much harder to establish is the number of active short wave listeners as the only thing to go on is information from the broadcasters themselves (listener figures are always to be treated with suspicion) or the number of shortwave capable receivers sold (but not necessarily used on the shortwaves).

But unfair remarks aimed at amateurs or shortwave listeners are not welcome. We are not, and have never been, a strange group in anaroks and often use the experience we have achieved in our radio communication to good use in emergency communications. HF is a long way from dead, and needs protecting. EMC regulations were set up to control this, sadly there are far too many things sold which blatantly fail them despite having little green stickers on them.

I repeat what ARRL frequently say in the USA, we are not against PLT per se but it should not interfere with legitimate users of the radio spectrum.

(I expect this thread, like the others, will soon be closed).

In reply to:

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"There are between 50 and 60 thousand radio amateurs in the UK"

How many of them are actually active ? I hung on to my licence for about 6 years after I sold all my gear, "just in case". I then realised that there was no way I was ever going to re-join a hobby that was so full of old farts who were stuck in the dark ages, so I stopped paying. I listen to 2m repeaters these days (those that are still on), and they're like ghost towns.

---

I don't know how many are active, I suppose it's between a third and a half on a regular basis and maybe two thirds on an occasional basis. But I could be wrong in that.

I know what you mean about those that look backwards, this is a big problem, forward thinking is needed.

As for the licence, now that the licence is free you can get it back and keep it active at no cost other than 20 quid to retrieve it. You may or may not want to do that