Antenna Basic Parameters (impedance matching)

Aerials can have any impedance, from a couple of ohms to thousands of ohms and may have some reactance as well. The impedance has to be matched to that of the aerial terminal of the receiver or transmitter, so as to transfer the maximum power. e.g. a "whip" aerial being used on very low frequencies might look like 10 -j1000, so you need an inductance of +j 1000 in series to make the aerial looks like 10 ohms (resistive). This value will need to be transformed up to 50 ohms to connect it to a transmitter for maximum power transfer. This is often done with a PI or T network.
Frank