There is a statement on the FCC website that says that Part 15 transmitters only get 500 foot of range. We get asked regularly how transmitters such as the AM1000 can legally get 1-2 miles range in view of this statement. After talking with FCC officials about the statement basically the opinion is that most AM and FM Part 15 transmitters are certified under Part 15.209 which is a radiation limitation. A Part 15 transmitter certified under this rule would get about 500 feet or so of range. AM transmitters certified under Part 15.209 are allowed 24000/F(Khz) micro volts per meter (at 30 meters) field strength. An example of this sort of transmitter would be a Childs toy or wireless microphone. However the AM1000 AM transmitter was certified under Part 15.219 which is not a radiation limitation but is a power and antenna length limitation. The power limit is .1 watt and the antenna and ground lead length limit is 3 meters. Another possibility is that looking at a case of a radio that was not sensitive, AND a radio band with high noise that Part 15 may only get a range of 500 feet, this is what the FCC may have been thinking when writing this statement, they may have been considering the sort of field strength that a full power station achieves. Part 15 is considered to be a “low range” service, it takes a sensitive radio and quiet band and careful installation to get good results.
here is no range or height limit for a Part 15.219 transmitter. With this allowed combination greater ranges are possible, though it requires tune up and setting the power by a competent technician. Generally you can’t buy a Part 15.219 certified transmitter bubble packed at the department store. Because the AM1000 has a removable antenna and adjustable power, instruction to be installed by competent personal was a condition of certification. Rule 15.215 (a) clarifies this: “(a) The regulations in Sections 15.217-15.255 provide alternatives to the general radiated emission limits for intentional radiators operating in specified frequency bands. Unless otherwise stated, there are no restrictions as to the types of operation permitted under these sections.”
Compare Part 15 walkie Talkies, the 15.209 "toy" type walkie talkies generally get about 200 feet of range, but the more expensive 100milliwatt type walkie talkies (especially those with sensitive receivers) can get 1/2 mile range and more.
In addition, the Part 15 rule was written in the 1950's when electronics was quite a bit different (Notice the rule mentions vacuum tube filament or heater power). It would be true that in some circumstances, any part 15 AM band device (there are over a million in operation) may only get 500 feet of range. A receiver that is not that sensitive, interfering structures, electrical noise in the band could cause low range. Again, Part 15 is intended to be a short range medium. The 1-2 miles range we advertise is under good conditions (sensitive receiver).
If you are concerned you are getting to much range from your Part 15 device it may be some natural feature, such as a river or lake that is carrying your signal. Or you may not have adjusted you unit properly, be sure to check all settings from the installation manual. Also your ground may be radiating a strong signal adding to your range, see
Ground hints to find out how to build or buy a ground filter.
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