Four-Way Aerial Switch

EE JULY/AUGUST 1987 by C Sanjay In many cases it may be necessary to switch between two or more aerials with minimum loss in the RF signal. Though this is not generally a problem at low frequencies, it becomes a serious one when the relevant signal is in the VHF/UHF range (50-960 MHz). The electronic switch de- scribed here keeps the switching losses minimal by making use of PIN diodes. PIN diodes are essentially current controlled resistors with properties that make them suitable for switching and attenuating RF signals. They dif- fer from most other types of diode in that rectification of the input signal only occurs below a certain limiting frequency. Above this frequency, the resistance of a typical PIN diode will change from 12 to 10,0002 when the control cur- rent is reduced from 100 mA to 1 pA. The circuit can switch up to four aerials, and is composed of two functional parts: the RF switching section, mounted onto the aerial mast, and the power supply & control section, ke...