[plug] TV interference (otopic)

[Steve Grasso]

>When my computer is on, I get interference on the TV in the way of red
>and green diagonal lines.  Some points
>1) The interference is only on Channel 9 (is this a good or bad thing
>;-) )
>2) The interference is coming from the box (not modem, screen or
>printer)
>3) The computer is in the room futherest from the TV
>4) There is an aerial port unused in the computer room

RFI from (typically older) computers mostly originates in the monitor and 
is best controlled at source ie. remove the computer to another room, or 
plug it into a different power circuit to the TV if possible. If not, there 
are three things I know of which may help (possibly by doing all three)

1.  Wind the TV antenna coax through a ferrite ring as many times as will 
fit (about three turns through a 2.5cm ring) before plugging it into the 
TV  -- ferrite rings from Dick Smith Electronics, Jaycar Electronics, 
Altronics etc

2.  Put an RF choke on the power cable of the computer, the power cable of 
the monitor and the monitor cable (if it hasn't got one already). The 
chokes should attenuate RF signals escaping the monitor/computer and using 
the cables as an "aerial". Put the chokes on the cables up near the 
computer case. RF chokes can be bought from the same place you get the 
ferrite ring and snap on around the cable. -- Putting chokes on all cables 
is probably overkill and considered by some unneccessary, but worth a go.

3.  Buy a commercial TV antenna RFI filter and fit it to the TV antenna cable.

(and an ugly but sometimes effective 4th idea:  cut out the flaps and one 
side of a  cardboard box, wrap it in aluminium foil, punch a few vent holes 
in it, and sit it over the back and sides of the monitor. The box should be 
big enough to not impede air circulation to the monitor)

Hope these help.
Steve