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Although JT Communications products are not approved for part 15 use, You may be able to use these products if you follow some simple guidelines.

Licensed FM Broadcast stations and their listeners have the right to unobstructed enjoyment and use of the FM airwaves. Unlicensed use has LIMITED privileges in regard to locally unused frequencies. Your unlicensed use has no absloute rights over the rights of licensed broadcast stations, or the rights of their listeners. If your unlicensed operation interfeeres with any other licensed transmission, your only choice is to CEASE operation or change the operating frequency of your unlicensed equipment.

Unlicensed operation of small transmitting devices in the US is covered in Part 15 of the FCC rules (47CFR15). It is best to obtain a copy from the Government Printing Office, or by contacting the FCC directly, via telephone or INTERNET. You can read more about low-power operation from the FCC location at This Specified FCC Website

If you want to locate the technical document that explains un-licensed operation, check out FCC BULLETIN # 63.


The FCC Rules specify a maximum field strength of your transmitted signal. Since it is unlikely that you have the equipment to measure the field strength accurately, it is useful for you to understand the theory of field strength so that you will know what you can expect from your unlicensed transmissions.

In 1989, the FCC revised its rules specifying a maximum field strength of 250 microvolts per meter at a measured distance of 3 meters.

The field strength of a transmitted signal decreases in direct proportion to the distance away from the radiating antenna. This means that every time you double the distance from your transmitting antenna, your receiver will only receive 1/2 of the signal voltage. However, when you are discussing power, it decreases by the square of the distance; for every doubling in distance, the received signal is quartered. Using the voltage theory, it is possible to create a chart to show the performance of your unlicensed transmissions under the Legal maximum field strength. The theoretical figures assume a simple 1 meter long receiving antenna, and do not take into account that reception can be increased with gain antennas, and/or preamplifiers at the receiving end. In the chart below, the field strength gets theoretically stronger as you move from the edges circular boundaries torward your antenna system.

FIELD STRENGTH COVERAGES WITH 250uV/m at 3 meters reference

METERS ----------FEET-----------FIELD STRENGTH (uV)---------TOTAL AREA
3                9.5             250                   304 ft.
6                19.7            125                   1216 ft.
12               39.4            62.5                  4865  ft.
24               78.7            31.25                 19458 ft.
48              157.4            15.625                  1.8  acres
96              314.9             7.81                   7.15 acres
192             629.8              3.91                  28.6 acres
384             1260               1.95                  114.3 acres
768             2519               0.98                  457   acres
1536            5039               0.49                  1831   acres
By restricing the maximum field strength at a specific distance from your antenna, the FCC plans for your signal to fade out at a somewhat predictable distance from your antenna. On the other hand, the FCC standards do make it legal and possible for you to broadcast on a school campus, campground, or local neighborhood, as long as you do not cause interfeerence to licensed broadast trasmissions.

How about "leaky cable"?

The FCC allows you to use leaky cable (radiating coaxial cable, usually buried underground to limit the maximum radiation), as long as you comply with the maximum field strength.

To see more on this topic visit  FCC LPFM WEBSITE


Last modified: May 5, 2013