Television Interference is caused by the receiver (the TV) not being filtered well enough to reject the transmissions from nearby transmitters (e.g. vacuum-cleaner motor, FM Radio stations, Amateur Radio stations).
If the transmitter is far enough away most of the time a high-pass filter like those you can get at Radio Shack will fix the problem. Install it on the antenna feed line as close to the antenna input to the TV as possible.
If you're still getting interference, try an FT-240-43 ferrite core (Don't use unknown material; it may not work.) Wrap about 10 turns of the antenna feed line (either coax cable or twin-lead) onto the ferrite core, installing it as close to the antenna input to the TV as possible. In some cases, you may also need to install an ac-line filter on the TVs power cord. They are available from Radio Shack (catalog #15-1111).
Some things that can interfere with your TV reception are rusty or corroded antennas and connectors on the antenna feed line. You should replace them if possible.
If you have CATV you can still get TVI because the Cable TV systems use the same frequencies that other services (like Police, Fire, and Amateur Radio) use.
Have you looked at the bottom of your phone or the back of your TV lately?
This device complies with part 15 of FCC rules. Operation is subject to the following two conditions:
(1) This device may not cause harmful interference, and
(2) This device must accept any interference received, including interference that may cause undesired operation."
You can get a FT-240-43 ferrite core from:
Toroid Corporation of Maryland
202 Northwood Drive
Salisbury, MD 21801