Interferance from PC/tuners...

[ricklous]

Hi,

A little mystery with which I'd like some help from the electrically minded among us...not a direct GBPVR problem, but I guess relevant to PVRs none the less.

Im setting up a new PVR with two Black Gold DVT-Ts, and very nice they are too. the only problem is that the PVR itself seems to be producing enough interferance to weaken the aerial signal...

After much faffing about Ive managed to arrange things so i can exclude pretty much everything other than the PC and the aerial flylead. So heres the setup:

SD-TV, fed direct from roof aerial.

PC, headless, sat next to TV. Power lead plugged in, aerial flylead plugged into the tuner, but 'loose' at other end. MCE remote is the only other external device. no s-video into TV, etc.

so, I tune TV to analog BBC2 (ie not watching via the PVR, which isnt connected to the TV anyway) and the picture is fine...press power button on the MCE remote, and within about 15 seconds, theres lots of thick black horizontal lines flowing across the TV picture. If I put the PC back to sleep, the interferance disappears. If i unplug the aerial flylead from the back of the pvr while its powered up, the interferance disappears.

So as far as i can understand...the PC is producing interferance, and the aerial 'boosts' it enough to affect the TV roof aerial lead, or the aerial being plugged into the PVR is causing some form of electrical interferance?

Has anyone seen this before? could the PC case be earthing or something? any other ideas? Ive been into Maplin and they were stumped, but thought putting a ferrite ring on the power lead of the TV might be worth a shot, which confused me more than ever....help!:confused:

[paperchaser]

Some PC's definitely put out RF. Not just the PC, but also certain peripherals, such as the hard drive, cd/dvd drive, external drives, graphics cards, etc.

Could be your case needs better grounding/shielding. People use all kinds of approaches for this from tinfoil to paints. Maybe try googling RF shielding for PC's and see what could work for you. Coils you mentioned work too sometimes...it is much trial and error.

[nitrogen_widget]

My experiance has been that it is the PSU that is a problem.
Cheap PSU's can be noisy when connected to some motherboards.

It can also be an "electrically" noisy fan causing feedback.

[martint123]

I'd have to say check the earthing of the TV coax, patch lead, wall socket etc. No way should any noise be able to get up to the aerial and back down again. Neither should PC noise be able to get straight into the TV (that's all part of the spec required to get "CE" approval).
I've got all sorts of junk next to a portable in the shack and the only thing that gives slight picture noise is a mobile phone when very close to it.

Martin

Can you try taking the PC to another TV system to find out if the TV or the PC is the problem item?

[ricklous]

Thanks for the suggestions Chaps

Can you try taking the PC to another TV system to find out if the TV or the PC is the problem item?

I knew i should have kept the spare TV i left behind when i moved! doh...

Neither should PC noise be able to get straight into the TV (that's all part of the spec required to get "CE" approval).

Thats what i thought, this TV really has been quite good to me over the years, Ive had it between massive floorstanding speakers in the past with no sign of them messing with it, so im assuming the signal is being dorked via the roof aerial lead (its a rented house) rather than the TV. Which gives me a catch 22 if i cant find the source...

Anyway, the missus is out on the drink tonight, so its an unbridled evening of geekery for me! will report back if i crack it

[ricklous]

Well, thought Id best report back on this seeing as stuffs now sorted...

Eventually got chuffed off with trying to fix the interferance at the same time as my signal getting worse as the weather got worse so everything got parked in the corner for a long time.

Finally got the aerial changed for a new digital spec one - so a really good signal at last - and for the PVR itself i took the job lot out of the case and the interference disappeared!

So now quite happy with my PVR. The wifes not, seeing as its a naked computer sat on the living room table with a spagetti tangle slung over to the TV, but Im sure if I leave it for long enough she'll get used to it

[Lindsay]

Must say I have a certain sympathy for your wife

Very strange that it's worse inside the case. You'd think the opposite would apply. Perhaps someone here may have a plausible explanation.

Good luck with the WAF!

[jbyram2]

Some computers have BIOS settings that reduce interferance..

on my computer for instance.

Hit DEL when it is first booting up

Under "advanced chipset settings"

Set "Clock spread spectrum enabled" to "yes".

This causes the clock frequency to waver a bit, and so keeps the computer clock from ever syncing with the TV scan rate to make bands of interferance..or so they say.

I havn't had an interferance problem, so I can't tell if this fixes it...but it's supposed to.

[ricklous]

This causes the clock frequency to waver a bit, and so keeps the computer clock from ever syncing with the TV scan rate to make bands of interferance..or so they say.

Thats one of the first things I tried :o

Also its not much further from the TV than it was so if it wasnt the case, I would have thought that the interference would still be there, and possibly worse seeing as the case isnt there to 'soak it up'. But I have a perfect picture now.

One thing that I think it might have been was the struts for the pci slots were wider than normal and had some funny slithers of metal stuck on the back that seemed to be designed to act almsot like those spongy draught excluders you can tape around a doorframe so it seals when shut. Im not sure weather they were there to keep noise from escaping the case or something? Anyway, with the aerials plugged into the tuners its possible they were touching the struts. maybe this was causing something funny between the case and the aerial lead...who knows. Im not a leccy guru...

[stustunz]

if you move the power supply close to the tuners does anything change
thats if you can