Some manufactures attempted to solve the interference problem by producing wireless microphone systems which operated in the 88-108 MHz band and were grossly over powered per the FCC regulations of the day. Some of these systems provided improved performance with less interference, however, they were illegal due to the large amount of radio power they broadcast, which according to the FCC could produce interference with standard radios such as in homes and cars. Nonetheless, during the late 70’s and early 80’s, lack of FCC enforcement allowed the proliferation of thousands of illegally or barely-legal wireless microphone systems to be openly sold in music stores across the USA. Because these wireless microphones operated in the FM band of 88-108 MHz, the band commonly used in car radios of the time, it was possible, when at very close range, to ‘break in’ over a legal broadcasts by music stations and be heard by drivers and passengers of nearby cars! Clint noticed that the battery life of these wireless microphone systems was poor due to the large amount of broadcast power they emitted. Some of the wireless microphone transmitters would become warm to the touch because they were consuming and emitting so much energy.
A low-power legal version of this technology was marketed through Radio Shack in the 70’s under the brand name “Mr. Microphone”. It used the 88-108 MHz frequencies to operate, but was legal because it radiated an amount of RF power below the FCC mandated limit. Consequently, wireless microphone transmitters which were operated with the FCC rules and regulations had a useful range of 10-50 feet under good conditions depending on the quality of the receiver and antenna, or a bit more range in ideal conditions. However, mainly because of the range limitation, these legally devices were considered a child’s toy. Many variations of this low powered, but legal, wireless microphone have appeared on the market since then. There surfaced yet another problem is ALL wireless microphones of the 70’s era, regardless of low or high power output, regardless of which frequencies on which they operated. The technical term for the problem was ‘multi-path interference’, or running into a ‘null spot’. This problem occurred when the wireless microphone transmitter interfered with its own operation. The radiation broadcast pattern of most wireless microphone systems of the day was omni-directional, generally