Abstract: A signal switching circuit includes an input terminal to which a signal is input, an output terminal from which a signal is output, a first electronic circuit and a second electronic circuit which are alternately connected between the input terminal and the output terminal, and switching elements for alternately connecting the first electronic circuit and the second electronic circuit between the input terminal and the output terminal through a selection. A signal alternative path for connecting between the input terminal and the output terminal at all times is provided. Even when the switching elements are in an open state, the signal that is input to the input terminal is output to the output terminal via the signal alternative path.

Abstract: A television signal transmitter includes a first frequency converting circuit that converts a television channel signal lower than a television broadcasting band into a first intermediate frequency signal higher than the television broadcasting band, and a second frequency converting circuit that converts the first intermediate frequency signal into the television broadcasting band and outputs it. An input amplifying circuit for amplifying the input television channel signal is provided at a previous stage of the first frequency converting circuit, and a band-pass filter is provided between the first frequency converting circuit and the second frequency converting circuit. The band of the input amplifying circuit and the band of the band-pass filter are a transmission band of a plurality of successive channels.

Abstract: A filter switching circuit includes first and second amplifiers, relays, and bandpass filters in which a bandpass filter having a higher frequency passband is selected by a smaller number of relays and the selected bandpass filter is connected in a decreased distance. A first relay is disposed near the input or output end of the first or second amplifier, respectively, and the other relays are positioned to correspond to the filters. The other relays are provided in opposite sides of a line connecting the output and input end, and the switching terminals of each pair of relays on the same side of the line are sequentially connected to one fixed terminal of each of the relays so that the other relays are sequentially connected to first and second fixed terminals of the first relay and each relay is connected to each second fixed terminal of each of the other relays.

Abstract: A filter switching circuit includes first and second amplifiers, relays, and bandpass filters in which a bandpass filter having a higher frequency passband can be selected by a smaller number of relays and the selected bandpass filter can be connected in a distance as smallest as possible. A first relay among the relays is positioned in the vicinity of the output end of the first amplifier or the input end of the second amplifier, and the other relays are positioned to correspond to the filters.