View Full Version : TV Interference

22-03-2002, 07:28 AM
I am running an 800Mhz Celeron which is situated about three metres from a television set and separated by two brick walls. On channel one the interference is impossible, continually rolling waves of thick lines from top to bottom. Channels two, three and four are fine, perfectly clean reception. I believe that the latter channels use UHF, whereas TV1 is on VHF. I suspect that proximity is the problem, but it would not be easy of convenient to put more space between the computer and the TV.
I have tried several things, including using a Belkin SurgeMaster for both power and modem lines, and interposing a large sheet of metal between the two sets - none successful. The computer was made by a local OEM, but they can offer no solution. Up until June last year my 133mz Pentium was running in the same position and caused no interference.
I like to surf whilst my wife is watching Coronation Street, but she has rebelled! Any suggestions greatly appreciated.

22-03-2002, 09:43 AM
You will probally need an outdoor aerial - no easy way out on this one. Sky satellite would fix it - pacify your wife and watch sport yourself.

22-03-2002, 10:01 AM

We have an outdoor aerial and the feed to the set is by coaxial cable. The aerial is about 15 metres from the computer.


22-03-2002, 10:02 AM
what part of the country are you in and where does your tv signal come from?

check to see if its the montior or the actual 'box'.

the quality of the case seems to make a bit of a difference.

22-03-2002, 10:06 AM

I am at Pleasant Point about 20kms West of Timaru and the TV translater is a couple of thousand feet on the Hunter Hills to South. Good positioning for a strong signal I'd say.

Yes, I queried the computer box with the local OEM and it's all metal and (they say) should provide adequate screening. I wonder what it does to the neighbours TV - no complaint so far.

22-03-2002, 10:28 AM
Can you try temporarily disabling your case fans to see if that makes a difference..or like Tweake suggested turn of your monitor to see if that does it.

Really the first step is to try and identify exactly what part is causing the interference.

If it isnt the fans or screen try removing your cards 1 by 1 to see if that makes a difference (check with the computer shop to make sure it wont void your warranty first).

Now I forget the name of them exactly but you can get some donut shaped carbon rings that you can wrap fan wires and the like around to reduce interference.

Hope this helps.....

22-03-2002, 11:00 AM

You won't solve TVi problems very quickly with hit or miss techniques. The most inportant thing to do is to identify the frequency that is causing the interference. Fans & power supplies don't usually cause the type of problem you describe. It is most commonly a radio frequency signal rather than a switching artefact.

My time is limited today so I can't give you a full response right now, but go to the Press F1 archive for 15-02-2002 and you will see a similar problem described. Read my reply to that post and see if you can identify the answers to some of the questions I posted. It may be possible to help you out quite easily but I need to know some details. Post any facts you can get (your local TV shop can tell you what the TV1 frequency is) and also post your computer bus frequency.


Billy 8-{)

22-03-2002, 03:51 PM
Try unplugging the external aerial. If you haven't got an internal aerial, just hang a few feet (say 3-6 ft) of wire in the centre connector. Look at channel 1.

If the noise is gone (or MUCH reduced) a strong possibility is that the far end of the coaxial cable has rotted out. But check the Belling-Lee plug at the set end too ... it's easier to get at.

It's amazing what a good aerial the outer of a coaxial cable can be. However, that's not it's supposed to do, and it's very good at picking up noise as well as the signal you do want. A tuned Yagi is better at getting the wanted signal. But the Yagi does need a good connection to the receiver.

22-03-2002, 04:19 PM
Billy T
Thanks for your comments. I could not find a post at 15th February 2002 on this topic in your name - I searched several days either side without luck. However whilst checking out the various frequencies as you suggested, I gained some other suggestions locally.
The Techie who assembled the machine suggests that it may be a power unit fault, like a capacitor breaking down and he is quite happy to check that and change the power unit if necessary. The computer BUS frequency is 66Mhz.
In tracking the TV1 frequency I spoke to a local electronics firm of my acquaintance where the principal is both a satellite TV installer and a ham radio enthusiast. He seemed to think that the power supply is the most likely culprit and suggests installing a Faraday shield on power cable. This apparently consists of a series of small ferrite rings on the cable itself and adjusted until the interference disappears. He will drop off a specially doctored computer power cable tomorrow morning for me to try. But he was not too sure about the TV1 frequency because apparently they deal in channel settings rather than the actual frequency when tuning.
So, I rang TV1 in Christchurch where a technical man told me that the channel frequency is 65Mhz - only one meg from the BUS frequency. He also commented that if the computer power unit is properly earthed to the computer case then no emissions should escape. He also mentioned that a spike arrester might help, but I am using a Belkin SurgeMaster for both power and modem lines - to no effect on this problem.
So I expect it?ll be a process of elimination. I guess others with similar problems would be interested in your comments, but you can reach me direct at abdi@clear.net.nz. Many thanks - now that I have the bit between my teeth I?m determined to get to the bottom of it!


22-03-2002, 06:01 PM
The interference could also be carried by the mains, especially if the TV supply is on the same loop as the computer. The power cable with ferrite beads sounds a good idea. One can also wind a power cable through larger toroids to damp down radio frequency transmission. It's possible the Belkin device is intended primarily to remove spikes and may not necessarily be an effective anti-RFI suppressor which would normally have a common mode rejection choke and a few capacitors to earth and across the lines.
It would also pay you to get your earthing system checked out, if there is anything fauly in your mains wiring then that will cause problems.
RFI is a very difficult thing to cure.

22-03-2002, 08:14 PM
Oh, bollocks. It's Microsofts fault. Must be.

23-03-2002, 12:48 PM
How old is your houses wiring?
i'm serious, if you are having things interfering with each other, the problem may come down to dodgy earthing in the socket your pc's powered from, or in the plug you TV is running from. Older TV's need earthing. If you are confident with a multi meter, check that there is 230-240 volts not just between phase and nuetral (the power source) but also between phase and earth. If not, you may have found the problem! If this is the problem sorce, sort it before a fault kills you!
Sometimes making sure that 2 items that effect each other are not connected on the same circut (fuse) is sufficiant to remove this effect. It is loosely comparable to the fridge that makes the stereo 'thump' each time it switches on, interferance can travel through the mains.

25-03-2002, 12:07 PM
Hi Bill

How are you getting on with the interference problem?

I stand by my view that it is not power supply or mains electrical in origin but I'm willing to learn if I'm wrong.

The most likely cause will be a combination of effects i.e. weak TV signal + faulty antenna/feeder + computer motherboard not earthed properly to the case & allowing the computer BUS frequency to leak out.

Post a report on progress.


Billy 8-{)