The following lines were added (+) and removed (-):
A more convenient generation of intercom systems became available for the average home user which placed a radio frequency onto the home electrical system itself. Typically these operated in the 49Mhz range and the RF signal was combined with the electrical wiring. When you plugged the unit into AC power, it not only provided power for the unit it also provided the home electrical system as a conduit for the radio communication between units. Effectivivness varied from home to home. Sometimes these units only worked properly within the same electrical phase so that half of the home wall outlets would not hear intercoms connected to the other half. Newer homes sometimes utilize filtration within the circuit breakers rendering these units ineffective unless all connected within the same breaker electrical circuit.A more convenient generation of intercom systems became available for the average home user which placed a radio frequency onto the home electrical system itself. Typically these operated in the 49Mhz range and the RF signal was combined with the electrical wiring. When you plugged the unit into AC power, it not only provided power for the unit it also provided the home electrical system as a conduit for the radio communication between units. Effectiveness varied from home to home. Sometimes these units only worked properly within the same electrical phase so that half of the home wall outlets would not hear intercoms connected to the other half. Newer homes sometimes utilize filtration within the circuit breakers rendering these units ineffective unless all connected within the same breaker electrical circuit.Then a third generation of wireless intercom was introduced utilizing a short antenna and operating in the FRS UHF radio spectrum. These had the convenience of not requiring the additional wiring of the closed wire systems while while overcoming the signal blocking issues with the RF over AC design. Furthermore, it was never really a good idea to place RF on the AC line as that is considered unwanted harmonics by most electrical engineers. FRS intercoms worked well until the FRS spectrum became over crowed in dense urban environments. Also, there are privacy concerns when transmitting your intercom activity over the open airwaves especially on the FRS spectrum where listeners owning inexpensive blister pack walkie talkies can monitor. Then a third generation of wireless intercom was introduced utilizing a short antenna and operating in the FRS UHF radio spectrum. These had the convenience of not requiring the additional wiring of the closed wire systems while while overcoming the signal blocking issues with the RF over AC design. Furthermore, it was never really a good idea to place RF on the AC line as that is considered unwanted harmonics by most electrical engineers. FRS intercoms worked well until the FRS spectrum became over crowed in densely populated urban environments. Also, there are privacy concerns when transmitting your intercom activity over the open airwaves especially on the FRS spectrum where listeners owning inexpensive blister pack walkie talkies can monitor. Over the years various models of Radio Shack intercoms varied in quality and reliability. In reviewing many different models the [[RadioShack 14 Channel FRS Base Station 21-1845]] seemed to have the greatest overall appeal for most home or small office setups. The use of CTCSS tone encoded squelch helped to overcome some of the issues with FRS congestion in urban settings however, did not provide any actual privacy. The units required frequency and tone set by small dip switches on the bottom, which might be too confusing for some users this had some clear advantages. Later models suffered from "too many buttons" on the top and could easily be tuned off frequency by accident. As long as you had one competent person in the office or family to set the dip switches, you could be more confident every intercom remained on the correct channel with the correct CTCSS tone setting. As long as you did not discuss private matters on the intercom system, these units really were some of the best wireless intercoms ever produced by anyone.