AdvancedA-005-006-002
How does intermodulation interference between two repeater transmitters usually occur?
A
Answer
Antennas and transmission lines
Type
A
When they are in close proximity and the signals mix in one or both of their final amplifiers
B
When the signals are reflected out of phase by aircraft passing overhead
C
When the signals are reflected in phase by aircraft passing overhead
D
When they are in close proximity and the signals cause feedback in one or both of their final amplifiers
Answer Notes
Intermodulation interference typically occurs at sites where multiple transmitters are located in close physical proximity, such as a shared repeater tower or a multi-transmitter vehicle. The strong RF signal from one transmitter can travel down the antenna and transmission line of an adjacent transmitter.
Once inside the final amplifier of the second transmitter, the non-linear characteristics of the amplifier circuitry cause the two signals to mix. This mixing generates unwanted sum and difference frequencies that are then radiated out of the antenna as interference.
Options mentioning aircraft reflections simply describe multi-path propagation and do not generate new frequencies. The option mentioning feedback incorrectly describes self-oscillation rather than the mixing of distinct signals.
Previous · A-005-006-001
If the signals of two repeater transmitters mix together in one or both of their final amplifiers and unwanted signals at the sum and difference frequencies of the original signals are generated and radiated, what is this called?
Next · A-005-006-003
How can intermodulation interference between two repeater transmitters in close proximity often be reduced or eliminated?