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[Marks DTM Calib]

Right

1) How many of your items (in this setup) use the earth pin.....I suspect none (as is common on double insulated items these days) so ignore the mains earth.

2) Do you get interference with a single link from the a piece of equipment to the TV, in this scenario you cant have a ground loop....

The princpile of lopps should be overcome by your switch box as this should be the star connection point in the setup.....with the TV and ancillaries being the leaf and route points.

Is there a TV earial lead connected to the TV via another pice in your setup?

[Kevin Wood]

I also doubt it's a ground loop as such because 99% of this type of equipment is double insulated and doesn't have a ground connection from the mains supply. This means your only ground connection between the units is via the signal cables, and this ties all the grounds to the same potential. You should probnably avoid trying to connect other grounds to the devices as this is exactly what causes a ground loop.

These are classic symptoms of mains hum getting into the video signals, however.

My money is on either poor screening of the cables, or a poor connection of the screen as it enters one of the appliances.

Another possibility is that the power supply of one of the devices is breaking down and either passing "mains hum" into its' DC outputs and affecting the quality of signals passed through it or, more worryingly, the isolation between the mains and output is breaking down and causing leakage of AC current.

As Mark said, it's key to determine of this "hum" is present on the picture with only an RF source into the TV directly from the antenna. If it is present, it points to a fault in the TV. When it is preseny, is it present with all source signals, including the TVs internal tuner, or only those connected

Next, try different combinations of peripherals connected and see if there is a pattern. As you have said, it's good practice to separate the signal cables from mains cables and also from devices such as mains adaptors which contain transformers.

Many external switches for video are pretty poor quality. Can you not connect the devices to SCART sockets on the TV and switch them internally? You will benefit from a better picture as this avoids PAL encoding and you can eliminate a component from the system.

The reason you don't see many "braid breakers" for video signals is that the audio devices are just a transformer. Since video signals require frequency response down to DC, and very good transient response with no "ringing", isolating a video signal is an order of magnitude more difficult.

Another thought. You talk about CCTV? Is this a wired system? If so, could it be that the video signal from this is grounded at the remote end of a long cable?

Kevin

[Plomien]

if you plug them in without the RCA do you still get interference?
I was getting screen interference and it was my scart splitter causing the problem

[Martin_1962]

I use one of these and the picture is great.

Composhite is always a last resort signal, always try to use RGB or component

http://www.vtx.co.uk/video/trilogy1.htm

[Martin_1962]

[STMO123]

Just try a different telly.

[mv6copcar]

Thanks to everyone who helped out on this one - i had the engineer visit me from the shop where i brought all the cables and adaptors from, Get this - - The scart switching unit i use (same as pictured above) has a 12v dc tranny (built into the plug) this was leaking ac signals everywhere, when turned on he picked up static from the other side of the room!!!!!!!!
the second he unpluged it - perfect picture.
so even though everything i could disconnect was disconnected, the plug 12v tranny was still emitting noise/signals.

SORTED! thanks again people!