Now, it would be of some help if you had a fellow ham with a H/T to help you in this endeavor. This way you can operate the packet station and he or she can tell you if the RFI is still present at the television. If you use the H/T on low power, you will probably find that it is about the same signal strength as the packet station. If it causes the same type of interference, it will let you do a lot of troubleshooting right in the neighbor's house.
These steps can be approached from many different directions. Choose which is easiest for you. But for an example: Take the antenna leads off of your TV or cable converter if this is what receives cable channel 18. Terminate the antenna input on the equipment with the proper resistor. 300 ohm for a 300 ohm set and 75 ohm for a 75 ohm set. Keep the leads as short as possible. Transmit on 2 meter packet. If you still have RFI, there is a good chance that the RFI is entering through the A/C line, or being directly picked up by the television circuitry. Wrap the A/C line around the toroid. Transmit again. If the RFI is eliminated or reduced, you have found the path and cured the problem. If the RFI is still there, check to see if there are any other wires or conductors attached to the TV. Remember, any thing that can transform itself into an antenna, can be the source of the RF current. If this is the case, more experimenting with more toroids may be necessary. Now after these areas have been eliminated and the RFI is still present, the RFI is either stronger than the toroids and more turns or toroids are needed or the RFI is being induced through the case of the TV.
If this is the case, you may need to stop right here. Most state laws prohibit you from fixing your neighbor's TV without a state electronic repair license. Besides, if anything goes wrong when you have the back off the set, you will be assuredly (and expensively) blamed! Contact the set manufacturer through the Electronic Industries Association (EIA), 2001 I St NW, Washington, DC 20006. The EIA maintains a database of EMI/RFI contact persons at each of their member companies.
On the other hand, if after you properly terminate the cable input with the resistor, and the RFI disappears, then you know that the RFI is entering via the cable before your TV. This can either be via common-mode on the shielding of the cable coax, or by the RFI penetrating the shield of the coax itself and entering via the center conductor. The latter is a more difficult problem to fix and you may need the help and cooperation of your cable company, and a lot of perseverance.
A quick check to see if there is leakage into the cable system is to determine if there is leakage out. Tune your H/T receiver to 145.250 and see if there is a carrier present. If there is not, or only a very weak one, then the cablesystem itself is "clean". You will have to look elsewhere.
This method of locating the path of the RFI current and eliminating it can be used with most all types of appliances and radios. You just have to use the process of elimination. Now there are a number of factors that we really can't do too much about. Some televisions have only a 300-ohm balanced input. For these TVs, we need a 300 - 75 Ohm transformer in line. These pieces of equipment have been known in many instances to be a major contributor to the problem. In many other TVs, you have a coaxial 75 ohm input, but your TV converts it right back to 300 ohm inside the case! And in the cases where the RFI is induced through the case of any essential piece of equipment, depending on what piece of equipment is suspect the only things that you can do are:
Contact a licensed television repair technician if your television is suspect and see if the television can be modified to prevent RFI. Some manufacturers have good information about these types of modifications.
Contact your cable company if their cable converter box is suspect. Reduce the intensity of the Electro-Magnetic Field. Increase the distance to the Electro-Magnetic Field. Or, shield the equipment from the Electro-Magnetic Field.
(Continued in Part 7)
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