I have to pass the TV signal cable near the power cable for lighting in my room, and I observed noise in the TV. If power and signal cables are near each other, does the power cable have a magnetic effect on the TV signal cable?
Power line noise can couple into low voltage signal cable easily when the cables travel close to each other in a parallel direction for any amount of distance. As you may guess the longer the parallel run and the closer the two cables the more chance of coupling and disturbance.
There are additional considerations to consider as well...
- Coupling potential falls off dramatically with increased separation between the cables. Doubling the distance can make a huge difference.
- Quality of cable can make a huge difference. There are many grades of TV signal cables and ones with high quality construction and internal shielding can make a huge difference.
- Noise on the power line can often be attributed to other equipment plugged into the circuit. This can even include equipment that is plugged into other circuits in the building but fed from the same power panel. Sometimes noise on the power line can be significantly reduced by using a plug-in power line filter between the noisy piece of equipment and the wall receptacle.
Anything with an electric charge has an electromagnetic field that exerts force on anything else with it’s own electric charge. In your case the power cable’s field is physically changing the signal on the tv cable (the tv signal will also affect the quality of the power delivered on the power cable but this effect will be minimal).
Technically this field is infinitely large and weakens with distance but practically for household situations a few inches is usually enough to be effectively nonexistent unless you have very sensitive devices (like radios).
The problem is especially bad if wires run parallel to each other for some distance. Crossing two wires at 90 degrees is usually fine, running side by side for several feet is often unacceptable. It also depends on the equipment (video/audio are usually problematic) and cable (some have shielding, though it’s never perfect).