1. Q. Is broadcasting on AM or FM legal without a license?

The FCC and Industry Canada do permit broadcasting on the commercial AM and FM bands without a license provided power levels are kept low. This is typically referred to as 'micro-broadcasting' since the coverage range of a 'clean and easily detected' signal stays within a 1/4 mile of the transmitting antenna.

In most FM (VHF) applications a transmitter with an RF output less than 100 milliwatts sent through 50 feet of coax and coupled into a half wave dipole antenna creates the maximum signal permitted. For AM (Medium Wave) a combined coax and antenna length of 10 feet does the trick.

In Canada, a higher output on FM frequencies 88.1, 88.3, 88.5, 107.7 and 107.9 is permitted. Roughly a 250 milli-watt transmitter, hooked up to 50 feet of coax and a half-wave dipole antenna will create a signal close to the maximum.

Government regulations are based on actual radio wave field strengths and distance from the transmitting antenna. The specifics of this are discussed further on this website CLICK HERE!

[Back to Top]

2. Q. What do FM and AM mean?

FM stands for Frequency Modulation. This technique involves injecting the audio signal into the RF carrier in such a manner that the actual carrier frequency swings in direct proportion to the waveform of the audio. The power level of the carrier remains relatively constant.

AM stands for Amplitude Modulation. This technique involves injecting the audio signal into the RF carrier in such a manner that the power level or amplitude of the transmitter swings in direct proportion to the waveform of the audio. The frequency of the carrier remains relatively constant.

[Back to Top]

3. Q. How high should a micro transmitter's antenna be?

Commercial FM radio falls in the VHF band where line-of-sight suggests the maximum range of signal converge. Licensed FM radio stations combine powerful transmitters with antennas placed on towers and buildings, high above the average terrain, and so in fact slightly surpass this line of sight limitation. Often several antennas are placed along one tower and fed by a single transmitter so as to maintain optimum signal density close to the ground. The understanding here is that a signal that can be detected 100 miles away is of little use if it cannot be detected easily by the average listener at ground level.

A micro transmitter has insufficient power to reach the line of sight potential provided by an antenna placed high above the ground. Long coaxial feed lines eat up power as well. Typically a micro transmitter works best with an antenna less than 50 feet above the terrain since this will provide an optimum balance between ground level signal density and range. Ideally the feed line should be kept under 50 feet and the antenna kept away from nearby obstructions.

--->

Commercial AM radio falls in the Medium Wave band where wavelengths of several hundred meters appear. Ground level signals of this nature tend to bend around the earth while skyward bound energy is absorbed or deflected by the ionosphere. Licensed AM radio stations use towers that are electrically insulated at the bottom from the earth so the entire tower in effect becomes the broadcast antenna.

Low power transmitters in this range of the radio spectrum benefit from antennas that are long and vertical which start close to the ground, however the rules mandate that the feed line and antenna may not exceed 10 feet in length.

[Back to Top]