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What is the impedance of a half wave dipole antenna
50 Ohms balanced
50 Ohms Unbalanced
300 Ohms balanced
300 Ohms unbalanced
If a transmitter output is of a different frequency to the resonant frequency of a dipole
the excess RF energy is converted to heat in the antenna
some of the wave is reflected back down the feeder to the transmitter where it heats up the PA stage
some of the wave is reflected back down the feeder to the transmitter from where it is reflected back towards the antenna forming a standing wave
The dipole transmits a signal that is lower in frequency than the signal that leaves the transmitter.
An ATU is used to
tune the antenna so that there is an SWR of 1:1
absorb any reflected power so that the PA transistors are protected
artificailly alter the length of the feeder so that it matches the impedance of the antenna
match the impedance at the end of the feeder to the impedance of the transmitter
Which of these is not a function of an ATU
acting like a bandpass filter to reduce harmonics and spurious emissions
matching balanced feeders to unbalanced inputs to transmitters
removing high RF voltages from antennas
Matching impedances below 50 Ohms
Most transmitters are designed to have an output impedance of