Question
What is the purpose of the notch filter found on many HF transceivers?
Answer Options
- A) To restrict the transmitter voice bandwidth
- B) To reduce interference from carriers in the receiver passband
- C) To eliminate receiver interference from impulse noise sources
- D) To remove interfering splatter generated by signals on adjacent frequencies
Correct Answer: B
Explanation
A notch filter is a highly selective filter in a receiver designed to remove or greatly attenuate a very narrow range of frequencies. Its primary purpose in an HF transceiver is to reduce interference from carriers in the receiver passband. This is particularly useful for eliminating persistent, irritating heterodyne whistles or continuous wave (CW) carriers from interfering stations that have bled into the desired signal’s bandwidth.
Modern digital notch filters are often automatic, quickly identifying the frequency of the interfering tone and applying a deep notch (attenuation) to that specific frequency, effectively silencing the unwanted tone without significantly affecting the quality of the desired voice or CW signal.
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