This invention is a modular active filter that can be inserted between the antenna and a filter of a pre-existing unit, so that it can still function normally, without noise from cellular phones. This unit is modular. A heterodyning unit is used with a prefilter/amplifier unit and a post-filter/amplifier unit. After down converting the signal, while heterodyning, the signal is put through at least one crystal filter to filter out the noise introduced by cellular phones. To make sure that the unit works well with a wide variety of antenna-receiver pairs, the resonant frequency of the filters of the pre and post amplifier/filter units is set to the center frequency that the antenna and receiver are designed to handle. In this way, only one type of unit needs to be manufactured for each frequency band. An example of such an operating frequency might be 900 MHz. This invention has two types of embodiments. In one type embodiment the local oscillator produces only one fixed frequency. In the second and preferred type of embodiment, the oscillator has a connector that can except input from a laptop computer, for example. A simple key pad might or any means for a user to generate a set of signals corresponding to the desired set of frequencies can also be substituted for the laptop computer. This user generated input is then used to determine the output frequency of the oscillator.

A spurious signal SSP whose frequency spectrum is located at frequencies [(N + (1/2)).fh] is multiplexed with a luminance signal Y so as to keep an interleaved relation between the spurious signal SSP and the luminance signal Y and the resultant signal is transmitted. When the spurious signal SSP is detected, the recording operation is inhibited. The spurious signal SSP is multiplexed with the luminance signal Y at a level such as not to exert an influence on the picture quality when the video signal is reproduced and seen by a monitor screen.

A band elimination filter includes an input terminal and an output terminal. A capacitor is coupled between a first terminal connected to the input terminal and a second terminal connected to the output terminal. The first terminal is grounded only via a first grounding point. The second terminal is grounded only via a second grounding point. A first acoustic resonator is connected between the first terminal and the first grounding point and a second acoustic resonator is connected between the second terminal and the second grounding point.

A spurious signal SSP whose frequency spectrum is located at frequencies [(N+(1/2)).multidot.fh] is multiplexed with a luminance signal Y so as to keep an interleaved relation between the spurious signal SSP and the luminance signal Y and the resultant signal is transmitted. When the spurious signal SSP is detected, the recording operation is inhibited. The spurious signal SSP is multiplexed with the luminance signal Y at a level such as not to exert an influence on the picture quality when the video signal is reproduced and seen by a monitor screen.

A television scrambling system in which a television signal is scrambled by means of placing a scrambling (or jamming) signal into the luminance signal spectrum on the transmit side. On the receive side, the jamming signal is removed by a Surface Acoustic Wave (SAW) notch filter. On the transmit side, pre-correction of the television signal is performed to compensate for amplitude and phase distortions introduced by the SAW notch filter. The pre-correction includes: inverting the television signal as a function of time; pre-distorting the phase of the time-inverted television signal in accordance with the phase response of the SAW notch filter; pre-emphasizing the time-inverted television signal using a first amplitude corrector having a phase response; restoring the television signal to a time uninverted state, such that the phase of the restored television signal is pre-distorted in accordance with the inverse of the SAW notch filter phase response; and pre-emphasizing the restored television signal using a second amplitude corrector having a phase response which is substantially equivalent to the phase response of the first amplitude corrector.