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:

---

"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

Thank you for a balanced reply, and thanks for the information on licence retrieval. Since I don't however, plan to return to amateur radio, I won't be seeking to get my licence back. Although the gear is now quite a lot cheaper in the UK than it was when I started 27 years ago, there is still the elitist element in amateur radio that I can't stomach. Some older amateurs wouldn't even talk to you unless the second character in the licence was a 3. I met lots of good friends too, and I keep in contact with most of them, and most of them aren't active now either.

I just wanted to reply to your post in particular to let you know that you are not alone.

I left for EXACTLY the same reasons and I have never renewed my licence or thought about it since.

I used to be in the Royal Signals, for five years and naturally I wanted to keep going to a certain extent when I left to join the Police, so I got my civvie Licence and carried on, and as you quite rightly point out, it was expensive in those days ! This was back in the early 80's and I had a room entirely for my kit in my flat at the top of a block of flats over the ice rink on the Queensway in Bayswater, London. I kept it up for about 18 months before giving up because of the very people you mention! Even though I was technically about 6 or 7 years into it, because I had only just got my civvie licence I was still a newbie ! ! ! !

But I know EXACTLY what you mean !

Yes, amateur radio does have that sort of tendency, and I suspect will eventually cause the death of the pursuit, assuming that people with a more forward-thinking mindset are not able to rescue things before that happens.

I've found amateur radio quite friendly. I suspect it all depends on which club and who you meet. I've heard stories of people being shunned in the past. Maybe things have changed. I've been on air with an M6 callsign (entry level licence, very new) and very basic setup and had help and helpful comments from others. For me it's a good way of using and keeping some of the skills I studied in my engineering degree, even though I went into computing instead, so for me it is a technical hobby as well as a social hobby.

Some points on the main subject:

28dB above the limit - that's a factor of 630 for those who don't think in dB.

The regulators must look at a technology in terms of its percieved benefit as well as its cost. The cost with this technology is that it intereferes with radio. As the bandwidth increases the amount of radio services it intereferes with also increases. Newer advances will start hitting broadcast FM radio, maybe even police and other services radio. Then more people are going to start noticing. I note that the device manufacturers reduce their signal strength in these areas, but it will still effect people in places with not so strong reception.

What of the benefit? For some it may be easier than WiFi or wired networking, but for many the existing technology should work well. WiFi occupies its allocated space in the radio spectrum. It has a new higher speed. Wired networks work so well. Some people install the cabling as they decorate. We just ran it under the carpet around the edge of the room until we moved to wireless. Is this technology really important to "Broadband Britain"?

Another aspect is that this is your data that is being broadcast. I don't know whether the technology encrypts it or not. The signal is likely to be carried along the mains wiring to your house as well as through the air, so is there an increased chance of mutual interference between users if more and more people start using this?

Nothing like digging up an 18 month old thread.

I'll have to remember why I searched for it now. Some recent news on the subject I think.

Well 18 months has indeed passed... But BT are still pushing these things, the interference complaints continue, and some of the original people who have got Ofcom to investigate cases have still not had them resolved. Ofcom continue to insist the problem does not exist and refuse to act despite a recent very critical independent report commissioned by them. The only change is that we now have Gigabit PLT devices which block out band 2 FM and DAB radio as well as the shortwave bands.

But I appreciate this topic is not considered for discussion on these forums.

I make quite heavy use of 2m, as part of a local repeater group and part of RAYNET. RAYNET tends to be weaker signals as control is about 30 miles North from me and I currently live in a dip.

I'm currently listening to another control station about 20 miles South talking about an event at the weekend in which it seems lots of charity walkers did a serious hike not prepared for the bad weather that came in. Hills can be dangerous. Without mobile phone coverage, amateur radio is very good for providing safety communications on these events.

Last weekend I was involved with an event around town for which we used lower power walkie talkies. Increasing interference would be a problem in that situation too. One of our people lost contact when they moved too close to a certain white goods store for example. Of course we're not the only people in town using 2m walkie talkie. There are a fair few shops and security firms on these frequencies.

I think a few people would start noticing DAB failing and lots would notice FM. DAB is weak here. I've helped some people with antennas because those that came with the radio didn't work. Would people know to blame these devices though, or just blame DAB? The local FM station is very strong. National stations are comparably weaker.

The EMC laws do exist for a reason. It is bad that corporate interests are being allowed to ride roughshod over them.