TVI Solutions 101

[THUMPER]

TVI Solutions That Might Help

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The steps listed below may help you to eliminate TV interference that you experience from CB, amateur or other two-way radio stations. High-pass filters, common-mode chokes (choke filters), snap-together ferrite cores and ac-line filters are available from local electronics and department stores. A list of sources of filters is also provided at the end of this book. Remember, if your TV set or VCR has insufficient filtering or shielding, you may not be able to correct the interference yourself. You will have to obtain help from the manufacturer.



1. CB or Amateur Interference: Check to see if the TV volume control affects the interference level. If it does, install a "high-pass filter" at the antenna leads. This is a filter which will not allow signals in the the low part of the radio spectrum to pass through it. The name "high pass filter" is all you need to know to purchase one. If the TV volume control has no effect on the interference level, go to step 4. If you still receive the interference after installing a high-pass filter, go to step 3.



2. Two-way FM Interference: If you are receiving two-way FM transmissions, such as police or taxi, you may need to install a "notch" or "band-reject" filter at the TV antenna leads. The filter must be designed to reject the specific transmissions that you are receiving. The electronics dealer where you purchase the filter should be able to assist you with your selection. If you still receive the interference after installing a notch filter, continue to the next step.

3. Install a common-mode filter and/or common-mode choke at the TV input. If you still receive the interference, go to the next step.

4. Disconnect the antenna lead from the TV set. If you still have the interference with the antenna disconnected, install an ac- line filter at the electrical outlet your TV is plugged into.



Try wrapping three or four turns of the TV set's power cord through a ferrite core. Do this as close to the TV set as possible. You may also install a ferrite core on the antenna coaxial cable where it enters the TV set. You local electronics store will know what a ferrite core is and willl help you select one.

VCR ISSUES

Your VCR is really a television receiver without a screen. If your VCR is receiving interference, replacing connecting wires with shielded wire (coaxial cable) or replacing push- on connectors with screw-on connectors may solve the problem. The solutions for interference from two-way radio, broadcasting, and paging, described for television interference above, also apply to VCR interference. If these do not work, contact the VCR manufacturer for alternative solutions.



TELEPHONE PROBLEMS

1. Disconnect all of your telephones and accessories such as answering machines and take them to one telephone jack. Connect each instrument, one at a time, and listen for the interference. If you hear the interference through only one telephone, the interference is being generated in that unit.

2. Install a filter on the telephone line cord at the end nearest the telephone and/or at the telephone handset cord.

Filters are very selective. They must be designed for the type of interference your are experiencing or they will not work. For example, if your phone is reacting to an Amateur or a CB radio transmitter, install a filter designed for that purpose. FM broadcast interference requires a filter designed to reject FM broadcast stations. AM broadcast interference requires a filter designed to reject AM broadcast stations, etc.



3. Filter the incoming telephone line with ferrite beads and snap-together ferrite cores. You may need to experiment to find the best style of bead or core and the best location on the cord.



4. If you cannot eliminate the interference using the above techniques, you should consider purchasing a interference free telephone which has been specifically designed to be immune to interference.



Cordless telephones use radio frequencies and have no FCC protection from interference. If you are receiving nearby transmissions on a cordless phone your only recourse is to contact the manufacturer for assistance. The remedies above will not be of any use