By Ray St. Louis, PICO Products, Inc.
The concept of the Active Trap is an extension of the technology used for many years in the negative trap.
The Active Trap is a two pole, phase cancelling device with one pole fixed-tuned to the video carrier of the channel and the second pole tuned by voltage applied to a varactor diode. This square wave voltage causes the varactor-tuned pole to pass through the frequency to which the fixed pole is tuned. Each time this happens (47,118 times per second), maximum attenuation of the video carrier will occur. When the poles are not tuned to the same frequency, the video carrier attenuation will be at its minimum.
The difference in attenuation of the video carrier between the electronically tuned, then de-tuned condition of the active trap results in a 99.6% AM modulation of the video carrier with the 47KHz scramble signal. This scramble causes a permanent "overwrite" of the video intelligence and sync signal on the channel.