When switching an antenna between a transmitter and receiver, the 1N914 or 1N4148 can still be used, but with decreasing success as the frequency rises. It is common practice in VHF transcievers to use a PN junction diode, but with a lightly doped “Intrinsic” region between the P and N layers. The diode is called a PIN diode.

When the PIN diode is made to pass a current it has a low resistance, just like a normal PN diode. But when the curren is removed, there is a delay when charge carriers do not immediately recombine, resulting in a delay. This delay gives causes a phase shift and can give the PIN diode many other uses, such as police RADAR speed detector jammers. But the “more perfect diode” properties and OFF-delay are the ones relied upon to protect your nice 0.1uV sensitivity receiver from getting a 100-volt jolt.

When switch S1 is open, both D1 and D2 are not biased at all, so the antenna signal is passed through the 1/4-wave line to the receiver. When S1 is closed, current passes through RFC1, D1, and RFC2, so D1 effectively passes RF from the transmitter to the antenna.

Current will also pass through RFC3 and diode D2, so D2 will shunt any RF at the input of the receiver to ground. Teror RF SwitchingThe dead short across the receiver input is reflected to the transmitter as a high impedance by the 1/4-wave line. In this way the diode D2 will not shunt the transmitter/antenna circuit.

This technique can be built up to quite a complex arrangement requiring many diodes, and capable of handling 100s if not 1000s of watts, and at frequencies in the GHz region.