View Full Version : Interference

15-02-2002, 04:17 PM
I have a near new Athlon 1Gz, Asus A7266 mobo,Novia Model MS-300w (p4) power supply,256k ddr ram,Only cards are Nvdia gforce 2 Mx.mx video and riser card for 2 usb ports.This machine puts rf over tv1 picture.I have checked all earthing of mobo and ps to no avail.Even changed from a previous PS to this above.The case also is atx (new) Runs off UPS with no previous probs like this.Any help appreciated.

15-02-2002, 04:42 PM
You have the advantage that the owner of the equipment does want to fix it.

The usual list ... an external aerial for the TV should help. Don't run the TV and the computer off the same power point. As far as possible between the TV and the computer.

It might be the monitor, rather than the computer box (expecially since you have double filtering with the UPS). Monitors use switch-mode supplies too, and also have big currents in the video circuit. Try turning the monitor off (with the computer still running) to eliminate/prove that. If it's the monitor, you could try a filter on its power cord. (One simple power cord filter is a ferrite rod -- Dick Smith of Jaycars will still have them -- which you wrap the power cord around, close to the cabinet).

Since when has there been anything worth watching on television, anyway? ;<) .

15-02-2002, 05:46 PM
<<Since when has there been anything worth watching on television, anyway?>>

If Alister has a teenage daugher/s in his house, then there isn't much *not* worth watching!

So, tell me again, how do I make my PC do that to our TV?

15-02-2002, 05:47 PM
thanks graham.tried eliminating monitor.still the same.have large outside aerial.A

15-02-2002, 06:13 PM

RFI is usually straight forward to sort out but rather than take a 'hit or miss' approach, it is best to find out what the likely source is first before you embark on remedial options.

To start with, what region are you in and what channel do you use to receive TV1? I don't mean what number shows on the front of your TV (if any) I mean the actual transmitter channel. This identifies the frequency that is being interfered with. If you don't know, post the name of your local transmitter site and I'll look it up.

Secondly, what form does the RFI take i.e, is it closely spaced diagonal lines or jagged vertical lines; are they relatively stable or do they vary constantly; are they more prominent on particular coloured scenes or backgrounds; do they go away on black & white pictures?

I recently traced severe interference on TV3 in Auckland (channel 7) to a neighbour's computer running a 100 MHz bus. Bearing in mind that computer clock speeds are not all that accurate, the second harmonic landed slap-bang on top of the chroma subcarrier of 200.68 MHz, causing diagonal blue & yellow lines across the picture. The situation was aggravated by the computer being almost level with the customer's outdoor TV aerial and directly in line between the aerial and the transmitter in a poor signal area.

I agree with Graham that an outdoor aerial is virtually essential but direct interference via shared power points is very rare as both items of equipment will have power filtering to prevent EMI injection or reception via the mains. The most likely transfer medium will be direct radiation into the antenna/tuner of your TV.

Post more details and I'd be glad to walk you through the process. No cast iron guarantees of success, but we're eager to please!


Billy 8-{)

16-02-2002, 01:52 PM
One simple thing to try before you get too carried away: unplug the aerial cable from the set, and plug it in again.

The Belling-Lee plugs have always been a 'cheap' connector. They tend to get a bad connection if left undisturbed for too long. The reverse case: they show their mechanical fragility if unplugged and plugged too often.