Posted by: GW7AAV | July 19, 2010

Interference from Plasma TVs

Plasma TV’s are the Devil’s spawn. I really cannot understand anyone buying one unless they have not done their homework. I warned my eldest son but did he listen? No and now he is saying what I told him all along, that it just cannot cope with fast action. Anything moving quickly across the screen leaves a snail trial of colour behind. It is annoying to say the least, but not as annoying as the problem with timebase interference that can be heard on HF up to a half a mile away. I have not been up to my son’s house since he got his TV with any radio gear so I do not know if his is one of the dodgy ones, because not all plasma TVs have the problem, just most of them.

Ted Moore G7AIR wrote to me recently because he is having severe QRM on 80/40 and 20 metres. We were pretty sure from his description that it was line timebase radiation from plasma set. It appears every 20 KHz from about 2 MHz through to 30 MHz.

Ted had often dealt with Rod Wilkinson at Ofcom when sorting out special event licences and so he gave him a call. Rod referred Ted to Ofcom’s interference department and after filling in a form followed by numerous telephone calls he managed to get their nearest engineers to come out and give a listen. When they arrived Ted turned off his mains supply and ran his Alinco DX 77 on batteries so they could see that the interference was still there. After a few tests and some wandering about the results were inconclusive and they left asking Ted to do some tests and then contact them again. Ted was not overly impressed with the Ofcom engineers even though one appeared to be an amateur himself.

Ted started his own investigations. He travelled 5 miles due north, on the river bank miles away from any power lines or houses, there was no QRM. He then went about the same south of his QTH and tried again, no QRM here either. Then he had a breakthrough, half of the village is on one substation fed overhead lines, while Ted’s half is on another substation and fed from underground cables. His substation went off for an hour and the QRM was still there during the power outage. A few days later the electricity company advised everyone that power was to be off for a few hours for tree cutting at other end of the village only. He was listening at 0730 when it went off and so did the QRM. It came back on again at 1430 when they turned the power back on. Ted used a home-made 80m. loop, fashioned from a hula hoop and trimmed with a variable capacitor and was able to locate it as coming apparently from a house some 50 yards away. Ofcom seemed to be unable to do this as their DF equipment appeared to only be for use on VHF. Ted is now struggling to get them to come back but it is proving difficult. One of the problems may be that Ofcom are now no longer in charge of TV and broadcast radio interference as that has been handed over to the BBC.

If only Ofcom would actually police their own rules regarding the emissions from electronic devices problems like Ted is having would not be taking up so much time and effort from everyone involved. If there was any justice in this world the manufacturers of these things would not be allowed to put them on sale anywhere in the EC or at least the UK.

One problem having seen my sons Plasma TV is that they come with a set of ferrite chokes and instructions on where to fit them on the power and other cables. I wonder how many of the problem TVs have had the filters fitted and how many are sat in a draw or were thrown away because the buyer failed to read the instructions or understand why they were there?

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Responses

  1. well – in re my comments last month about plasma qrm. the guys from OFCOM came to my qth twice and we were set up on the second occasion to go hunting when it went OFF, makes one feel paranoid, was the perpetrator watching the goings on in my garden ? the day before their arranged third visit I got cheesed off at not being able to operate and went hunting myself using an Eddystone 40A receiver as used many moons ago by the GPO interference squad. found the house knocked on door and chap very apologetic listened, agreed and turned it off. all is well that ends well I guess. phoned Ofcom bod and told him all was now quiet on bands. one thing I very much appreciate is that their first task was check out my entire home and shack to eliminate my gear. turned off mains, dissed my large solar panels and battery system, noise still there. tedg7air


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