Why no channel 20 and 21?
In 1988 when narrow band RC channels were first introduced, RC channel 20 was found to create a problem when operating close to a channel 4 TV station. The problem did not affect the channel 20 users, but potentially affected all other channels. The wide-band single conversion receiver was the most popular receiver in use during this time period and was the receiver affected by the channel 20 problem. To understand how this problem occurs we must understand the internal workings of our receivers. The single conversion receiver has a front end (RF section) which is tuned to broad carrier frequency, this is followed by an IF (intermediate frequency) section, which was tuned to the industry standard 455 KHz. An oscillator is required in the receiver to beat against the incoming carrier frequency and produce the 455 KHz IF frequency. This beating of the frequencies, called heterodyne, is the basic operation that we call conversion today. The advantage of this conversion to 455 KHz is that
