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All posts by Ray Reed

Below are all of Ray Reed's postings, with the most recent are at the bottom of the page.

Resolve your interference problems | Freeview Interference
Tuesday 21 June 2011 1:32PM
New Malden

Hi, I'm new to your site and am hoping you may be able to offer some advice. At the beginning of April this year I began to get poor quality TV pictures on all channels via Freeview on my home TVs. An old analogue set seems to have poor quality pictures too. I am located in South West London, KT3 6LD, and have used the Crystal Palace transmitters with no problems for the last 20 years.

The problems I have include an overall compressed' look to the pictures, poor skin tone looking too pink and sometimes red or heavily sun tanned', overexposed highlights, particularly white, poor shadow detail, odd contrast, odd colours, particularly mauve and green, sometimes very soft pictures and darker scenes being too dark. I've also noticed that captions and news channel ticker tape' strings often stutter a little and become intermittently pixelated. The pictures often look very wrong on standard definition and similar, though less pronounced, on HD. These effects appear on two LED flat screens, one of which is a 9 month old Samsung C8000, and an old CRT TV.

I installed a new, good quality loft mounted, high gain, horizontal polarised, group A aerial when the new Samsung TV was bought. Again I have always had a loft mounted aerial with no problems. The aerial feeds a 4 way distribution amplifier. I'm a professional sound engineer with a background in radio. I have some electronics skills and carry out studio installations and first line equipment maintenance and have installed several aerial systems, amplifiers, cabling, etc. I've checked every connection from the loft down, remade coax and F type connections and disconnected the distribution amp all to no effect. I've checked signal strength with a basic DTV meter, which shows a high signal level, and have even run a coax cable direct from the aerial to one of the TVs with no improvement. I spent some time fine tuning the many picture options on the new Samsung TV and, before these recent changes, had what I considered to be a very good picture. I am unable to make any adjustments that make much difference to the poor picture quality I am now experiencing.

I've checked the BBC and Digital UK websites for information about reduced power or planned work at the Crystal Palace transmitters and see that there are no problems listed. I did wonder if anything had changed at the transmitters recently, lower power output, higher compression rates, bitrate reductions, any changes made to multiplexes in preparation for the digital switchover perhaps but I'm told there have been no changes.

I'm guessing the problems are caused by some sort of RF interference. I wonder if anyone is able to throw any light on the problems I'm experiencing or can explain the sudden poor quality TV pictures I now have.

Apologies for the long description. Thank you for your attention.

Ray Reed

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Thanks for your comments so far. I did think the signal may be too strong, though I could see no reason why it should suddenly change from its previous levels, so I disconnected the DA and put 1 then 2 attenuators on the line with no effect. I changed the original aerial as I couldn't remember what the spec of the old one was and wanted to give my shiny new HD TV the best signal I could. I tried moving the new aerial around the loft and put the old one back up, again no change. Interesting possibility re the Sandy Heath Tx as it coincided with the onset of my problems. Any ideas what I could do about it if it is the problem?

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GB flag

Thanks again for our suggestions. I would reiterate that the problem only surfaced in recent weeks after using the current set up successfully for many months and the previous TV for many years. Jm F, same problem on the channels you mention. Can anyone suggest or recommend an RF engineer of some sort in my area who could investigate the problem perhaps with spectrum analysers, etc?

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GB flag

Steve, I've now tried taking the front elements and reflector off the loft aerial to drastically reduce the gain with no affect. Also bought a basic set top aerial to try which just about gets a useable signal in one position. It may have reduced the problem a little but I'm not sure, if it has it's not by much. I do still wonder if it has anything to do with the increase to full power in other areas. My immediate neighbours get their TV via Virgin cable. I haven't canvassed any others, yet.
Mike, I tried bypassing the amplifier in the early stages of investigation and even ran a coax cable out of the loft direct to a TV in case there was a problem with the down lead, no change.
Mazbar, I think I'll have to admit defeat and do as you suggest.
Many thanks to all for your interest and suggestions. Please feel free to comment if anything else occurs.

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