Multiple transmitters can cover the area you need if one transmitter won't do the job. The most common method people are using to cover a larger area with multiple transmitters is place RangeMaster transmitters around town and link them by Internet, see this link. When using this method there are some important things to know. First you need to keep your audio in sync, even a few tenths of a second delay of audio between the transmitter s will cause a noticeable echo as a person drives between transmitter zones. Second, the RF carrier is not in phase sync using this method, the transmitters will not heterodyne (you must use the crystal controlled model) but the PHASES of the carriers will not be synced. Normally you will have a short zone of "flutter" as you drive between zones, not too noticeable, like driving under a power line. However if you don't do a good job of planning transmitter locations and get the transmitters to close together then the flutter will become worse. Do not try to use other (PLL) type transmitters with this method, you can get into all kinds of heterodyne problems.

See this FCC Publication addressing Multiple Part 15 Transmitters

We have other various communications from the FCC and Enforcement allowing the use of Multiple Part 15.219 transmitters

The way to design a system would be to generally plan a coverage are, put up the first unit and determine your coverage area. If you are getting 1.5 miles range then the next transmitter would need to go approximately 3 miles away. All the cells would be planned depending on the range attainable by the other cells and of course available locations. The idea is not to get the transmitters to close together and not to far apart. To close together and you have to much overlap, phase flutter and wasted coverage. To far apart and you have hole in you coverage. This is the Zerobeat method. With our system your coverage areas CAN overlap.

The Barix (see this link) product has provisions for audio synchronization.

Seek locations with a good ground when you are planning your site.  Typically if you see antennas and such at the site there is already a good ground there.

See this link for an example zerobeat diagram for 3 transmitters, however you can use as many transmitters as you like.

See this link for an example system for 2 transmitters, linked audio and radio carrier by microwave.

Here is an inexpensive microwave system prairietech

We recommend first of all using a good technical person that has worked with radio before. A good technical person can get more legal range just because they understand radio. What we recommend when setting up to cover an area is to put in one unit first to get an idea of what kind of range you will be able to get. Then design the location of the other units with the range of the first in mind. Range will vary widely according mostly to ground quality, installer skill, height, noise floor, ect.

Here is a link that describes many different methods of linking transmitters.

sync instructions               Sync guidelines         New Sync Manual

Using an Radio station type audio processor like an Innovonics 222 will make you signal sound louder and get you more range legally, however most audio links won't support the asymmetrical modulation output of the 222 so you will need a 222 for each transmitter. You can also you an old Audiomax or Volumemax audio processor.

Some customers have suggested that using a standard phone line to deliver the audio is acceptable, especially for talk radio.

Another method of expanding is to receive the signal of the first transmitter in the second location with a good quality selective AM radio, send the audio to another transmitter and rebroadcast the audio on a different frequency. The transmit and receive frequency have to have some good separation for this to work. The disadvantage of this setup is that you will be broadcasting on two different frequencies. Basically what you would be doing is using a Rangemaster Am transmitter to distribute your audio.

See for information on phone line STL links, says they can make your computer a phone line STL using software.

See this link for the Barix network MP3 player that will play audio right from you internet stream into the transmitter.

Here are some e-mails from tech support in response to us about the Barix Gold unit.