Tips on Choosing an Operating Frequency and avoiding TV interference

This requires Thought, Time, Care and Discernment. Do not proceed unless you are willing to do all of the above. Can't do it? Then stop now, or find someone who can help you. It is OK to ask for help.

It really is NOT sufficient to just check the FM band for an empty frequency using the average FM portable or desktop radio.

Note:

If running 100 milliwatts or less it matters little where you set up to transmit as your area of operation will be about 100 feet or less, and the chance of causing problems are nil.

If you are running 1/4 watt to 7 watts, your area of broadcast will be 1000 feet up to a few miles.

You could interfere and must take care NOT to do so.

Suggestions:

1. Do not operate with more power than you need. If you live in a town with its population within a radius of less than a mile, a one watt exciter is adequate. Use an antenna like a Desert Slim Jim and mount it as high as necessary to reach those around you. A higher antenna is always better than more power.

2. If your transmitting site is above the average elevation, that helps greatly.

It is your responsibility to carefully research what FM stations can be listened to using a very good receiver in your area of planned broadcast. Any distant station you can't hear with a very good quality, very sensitive, receiver, you can disregard.

Check the published listings of all existing Stations within your community and the surrounding 50 miles. Make a list of the Stations that are published. Then add stations you find that are not listed officially.

Some stations might be across a state line and it is important to note them as well.

The WWW has search engines for each frequency by state that may be useful for compiling your list. One webpage has a search engine that's programable to list published stations within a certain distance from your search area according to city name or zip code.

Find a "slot" that is two channels (400khz) away from an existing station. 3 channel "slots" away is even better.

Of all the open "slots" you find, Note the 3 most quiet "slots" by driving all around your planned broadcast area.

If you can, Disregard any candidate "slot" that has noise or a discernable station from far away.

You want the quietest "Slot" you can find as your listeners will be able to hear you better.

This is especially important, typically in the lower end of the FM broadcast band (88-92 MHz), where there are numerous overlapping medium power National Socialist Corporate Bottom Feeder Public Radio stations who are there in my opinion to help crowd out "INDY" LPFM volunteer stations that might provide an outlet for accurate local news and timely info. Your neighbors may be receiving a distant station using a good receiver and an outdoor antenna. Interfering with such reception is in violation of regulations but worse, it is bad form to interfere with an existing station, even what amounts to a borderline R.I.C.O. Enterprise in my opinion. NPR affiliates occupy 6 frequencies in my community. Half of them mirror the same content, little of it from inside our community. Obviously, this is to push out “INDY” broadcasters. Commercial Broadcasters pull a simular stunt, often using Translators to mirror their signals on an additional frequency or two in order to deny others from having a local station by filling up available frequencies. Translators are supposed to be used only in special circumstances where a mountain or other obstruction blocks the signal. The Translator concept is supposed to be a very low power operation to fill a dead area of reception, not to offer programming in another city, or Dual signals on the FM band. This is an abuse, which the FCC allows in violation of their own regulations. Another game played against LPFM is the use of Translators linked via Satellite from one source, typically it is a centralised corporate religious broadcaster offering music and the odd canned sermon, a K-Jesus station where no one is there. There is someone to talk to, -they will answer an 800 phone number where you can send them money. How nice.

Hopefully, you live in a free country where you are not subject to capricious and arbitrary Governance.

One way of finding an open frequency on the FM band is to check the band with a very good FM receiving system using an external antenna. If you do not have access to such a radio, most modern car radios with exterior antenna are very sensitive and usable to help you know what stations your neighbors really can be receiving on a particular frequency. A digital tuned AM/FM 1985-1989 Ford radio used in pickups and large sedans with an outside antenna are one of the best ever made. They are very sensitive.

Find relative higher ground in your area (not a mountain top, just the higher areas around your community) and scan the band and list every signal you can hear. Drive to the fringes of your planned broadcast area and do same from at least the 4 major points around the compass. 8 points around is even be better. Listen from higher ground when possible.

In choosing an operating frequency, remember that many digital-tuning receivers are designed to tune in 200 KHz increments and therefore might not receive a signal operating between these standard FM broadcast "Slots" (frequencies). Most licensed Stations will be on odd frequencies, for example 88.1, 94.3, 103.7 etc. Many modern digital tuning receivers will not be able to listen to "even" frequencies such as 88.0, 100.4, 107.6, etc.

It is your responsibility to determine carefully that your operation will not cause interference to any Radio Service, Other FM Broadcasters, Aircraft Bands, or even Television stations via second harmonics generated by your transmitter (exciter).

Harmonics: An Example.

After all your search and survey, Your three best "slots" are 95.5, 96.7, and 106.9 The concern here is possible TV Interference (TVI) generated at exactly 2 times your FM Frequency. This is called "second harmonic radiation" 23 and 44 miles to the south of you are large cities that have 5 TV broadcast stations operating on channels 2, 5, 7, 10 and 13. All of them transmit from a mountain top between them.

You want to transmit on a channel that avoids a second harmonic that lands on a TV channel in your area. Those that avoid channels in your area make "the final cut" We are not talking of TV Cable channels, but of open-air TV broadcasts that their customers receive with outside antennas close to your Operation.

TV channels 7 through 13 are a possible headache for low power FM operators, Especially if your transmitter is in a fringe TV reception area. In this example Channels 7, 10, and 13 are of concern here.

Reject 106.9 as it may interfere with TV-13 (2x 106.9 = 213.8)

Reject 96.7 as it is in possible conflict with TV-10 (2x=193.4)

Choose 95.5 as its 2nd harmonic falls on TV-9. There being no TV Channel 9 in your area,

in this example You are best served by homesteading 95.5 from the perspective of avoiding TVI.

Study Broadcast TV frequency ranges for each TV channel

174 - 180 MHz television channel 7

180 - 186 MHz television channel 8

186 - 192 MHz television channel 9

192 - 198 MHz television channel 10

198 - 204 MHz television channel 11

204 - 210 MHz television channel 12

210 - 216 MHz television channel 13

If all your neighbors have their TV antennas pointed south toward the distant TV stations and you are east or west of them there may not be any problem, especially at power levels below 7 watts. Ask your closest neighbors if you are causing them any problems. You want good neighborly relations. Potential TVI problems are most likely to sneak up on you at higher power levels, or someone too close to your station. A worst case situation might be you transmitting on 105.3 and just north of you is a neighbor pointing his antenna due south at TV-13 many miles away from you both. If the 2^nd harmonic signal is strong relative to the audio portion of TV-13 from many miles away, You have a problem. If you are on good terms with the neighbor, perhaps a good hi-pass filter installed on his TV will clean it up, along with a good low pass filter on your transmitter. If that does not do it, You have to choose a frequency whose 2^nd harmonic is outside any of the TV stations in your community.

There is the problem of signal overload if your neighbor is right next to you, It would be wise to not transmit if you overload a neighbors TV, either operate with their agreement at times when they are not watching TV or move the Operation to an other location away from TV viewers who use outside antennas. Or buy them Cable.

If you are transmitting at power levels above 7 watts, and have neighbors close by, you must use an inline TVI supression device like a Low pass filter from Progressive Concepts. The models: LPF-7000, up to 25 watts, LPF-7002, up to 125 watts. Ground your Antenna tower with at least one 8' grounding rod. This may help prevent some TVI and help to protect you from Electrical Storms as well. Do not build your own Exciter even if from a kit, unless you have a high level of technical expertise. You are better served to shop around and purchase something already assembled.

Some kits, like these from PCS are only $10.00 more in the assembled version.

Your time is better spent on Programming, Antenna and Frequency search duties.