Lighting interference with cabling


Active Member
I have 2 cables running from my a/v rack to my TV... 1 HDMI and 1 CAT5e

Due to contraints I have used my CAT5e as my Component Video cable.

When I have my fishtank metal halide lighting (140watt electronic ballast) on there is a thin red line of interference on the TV when using the Component, not the HDMI. So I know the TV and the HDMI are not the source of the red line. Must be the CAT5e cable.

The lighting is 6' and 2 walls away from the closes point of the equipment and cabling.

any ideas on how to cheaply fix this until I can get a proper cable?

Operating on the assumption that it is probably noise being induced onto the power lines (since it sounds like the video cabling goes no-where near the lights). . .

Is the fishtank on the same circuit? If it is, you could try moving it to a different one, if possible. Or maybe move the video equipment. . .

You could insert a power filter into

a) lights
:) source device
c) TV
d) video switcher (if there is one)

Another thing- if it is a powerline noise issue, changing cable types will not affect it.

And, since we are on Cocoon, I have to propose an automated solution-

Just monitor your IR commands to the TV, and anytime you switch to that input, turn the fishtank light off, and when you switch away (or turn off the TV) switch it back on. ;-)

What are you using for your Cat5 to Component? Do you have a seperate pair? You can try changing the wiring configuraton, but more then likely, like mdesmarais said, you are most likely injecting noise into the line. This typically happens through the neutral so changing circuits isn't going to do to much. Try some different line filters.
If you are not using baluns to convert between component video and Cat5 at each end, get the proper cable first instead of wasting money on "patches" and then see if you have the problem. Cat5 cable is not shielded. Component video cable is three coax (shielded) leads. You are probably missing the shielding and it makes a big difference.

Contrary to what many seem to believe, CAT5 is NOT good for EVERYTHING unless signals are properly converted before sending it over CAT5! And even then, an end-to-end shielded system beats a non-shielded system (Cat5) hands down, IMO.
huggy59 said:
And even then, an end-to-end shielded system beats a non-shielded system (Cat5) hands down, IMO.
I never thought I would be disagreeing with Huggy. Ever.

But I do now, just a little. When used as directed, a twisted pair system is much more noise-immune than a shielded system. Here is why:

A shielded system, such as a coax, tries to prevent noise from contaminating the signal. But noise can and does get through the shield, and the stronger the source of noise, the more noise that leaks in. The better the shield, the less noise that leaks in, but for more money per foot of cable.

A twisted pair system allows the noise to get in. It doesn't try to prevent it. But the purpose of the twists in the wire is to insure that the noise affects both wires equally. The signal is put on the two wires in differential form: usually opposite high and low for digital data, and usually opposite polarity for analog signals. The receiver simply subtracts the signal on one wire from the signal on the other wire. The result of the subtraction is that the signal is doubled, and the noise is reduced to zero (which is referred to as "common-mode rejection"). It doesn't matter how strong the noise is, it gets subtracted out, leaving an uncontaminated signal.

This is why RS422 and RS485 can run up to 4000 feet on unshielded twisted-pair in a noisy environment, with few errors.

A balun (for balanced-to-unbalanced) is a transformer that converts a signal to differential form (to balanced) and back again (to unbalanced) for use at each end of a twisted pair. It is the balun that subtracts the noise out of the video signal. It also electrically isolates the two sides, thereby eliminating potential ground-loops.

The baluns are the key to a good Cat5 system. They are truly precision devices, which is why they are so darn expensive.