Question
What creates intermodulation interference between two repeaters in close proximity?
Answer Options
- A) The output signals cause feedback in the final amplifier of one or both transmitters
- B) The output signals mix in the final amplifier of one or both transmitters
- C) The input frequencies are harmonically related
- D) The output frequencies are harmonically related
Correct Answer: B
Explanation
Intermodulation (IM) interference is a serious problem in repeater and commercial radio sites where multiple transmitters operate close together. IM occurs when two or more frequencies combine within a non-linear device, generating new, unwanted signals (IMD products) at predictable frequency combinations.
In the case of two close repeaters, the strong output signal of one transmitter leaks into the antenna system or output stage of the other transmitter. This causes the output signals to mix in the final amplifier of one or both transmitters (a non-linear device). The resulting mixing products then radiate from both antennas, causing interference to third-party receivers operating on the IMD product frequencies.
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