VHF and UHF switching
The switching of VHF and UHF signals presents problems that do not arise in the consideration of other switches. The frequency of the signals implies that even very small amounts of stray capacitance can be significant, and the inductance of the switch components can lead to the switch having a resonant frequency which may be in the VHF or UHF range. In addition, the switch will normally be located in a line whose impedance will be of the order of 50 0, and the switch should also have this impedance value in order to avoid mismatching on the line. Very simple designs exist and are used, for example, for switching the input to a TV receiver between an aerial source and a TV game source. These switches are not intended for anything other than casual domestic use, however, and have large losses. The better quality switches for this frequency range are of coaxial construction so that matching can be maintained, and the operation is more likely to be by solenoid. This permits remote control, so avoiding hand capacitance effects.
For switching signals at low level that are not on a line, mechanical switching is seldom useful, and has been replaced by the use of low-capacitance diodes, usually of the Schottky type. The bias on these diodes is taken through a well-decoupled connection to a remote switch, so that the main switching action is simply a low-voltage DC one. The design of switching for UHF/VHF signals at high-power levels is a very specialized matter and usually calls for a one-off solution rather than any form of off- the-shelf switchgear.