electrical interference

[stinkfoot]

Hi! I'm getting interference on my tv whenever I have my laptop plugged into the same outlet. I can't move the laptop since it feeds into the tv thru a vga to composite video converter. my tv system is all coax and composite connections (I have -gasp- 3 vcrs - I live remote enough that my county actually still has analog over air tv signals).

any suggestions on eliminating that interference other than the obvious (upgrade from my ghetto gear - which I'm working on saving up towards)? It's not as bad as vacuum cleaner interference, but still a significant loss in quality.

Thanks!
core

 

[Resqueline]

Is the interference present on all channels/inputs while the computer is plugged in? Or is it only present on the "computer channel"?
Can you remove the interference by disconnecting the VGA or composite going to the TV?
You can try feeding the various cables through ferrite cores and see if/where it helps.

 

[stinkfoot]

all channels - even when I'm not using the vga>composite converter, my antennea channels are still a bit fuzzy (so, all channels). The interference goes away when I unplug the laptop power supply from the outlet (sorry, should've mentioned that).

can you tell me more about ferrite cores?

 

[Merlin3189]

I have a problem with interference to my audio system when using my laptop. I believe that it originates in the PSU as it does not occur when running on battery, even when the laptop audio is connected to the system and the PSU is plugged in but switched off.
I get some improvement with ferrite rings, but I haven't yet solved it. I do think this is the right way to a solution, just need to get the right ones in the right places.
I'm trying clamp on ferrites - two half-cylinders of ferrite which are clamped round the lead by a hinged plastic holder. In the past I've used torroids (overgrown Polo mints) which the lead is passed through maybe 2 or 3 times. This requires that the lead be passed through the hole in this solid ring, so you may need to remove (& later replace!) a large plug to do it. I think these are more effective, so that'll be my next step: the clamp on ones were just easier to try first.

 

[stinkfoot]

Merlin,

someone just mentioned to me that ferrite clamps don't work and that we would need a pi circuit.

can anyone here confirm or deny that and possibly provide more information on how that would be implemented?

 

[Resqueline]

Ok. So is the noise there when you play the VCR's too, with the VGA unplugged but with the computer powered? If so you'll probably need a differential filter.

There are two noise propagation modes; common mode and differential mode.
The common mode is what is capable of radiating into an antenna system, and also setting up noise along signal cables between equipment.
The differential mode is only capable of entering equipment, say through the power lead, and radiate noise within this (standalone) equipment.
A ferrite clamp/ ring/ toroid takes care of common-mode noise but due to its limited # of turns they can only deal with higher frequencies. Prevents cables = aerial.
Common mode chokes has a substantial number of turns (high inductance) and are thus able to deal with much lower frequencies. Only one is needed.
Differential-mode chokes doesn't have as much inductance since the core has to deal with the supply current, and so has a limited lower frequency. Two are needed.
All power line filters contains at least one common-mode choke, one X-capacitor, and two Y-capacitors. Some filters contains two differential chokes as well.