Question
What problem can occur when using an automatic notch filter (ANF) to remove interfering carriers while receiving CW signals?
Answer Options
- A) Removal of the CW signal as well as the interfering carrier
- B) Any nearby signal passing through the DSP system will overwhelm the desired signal
- C) Excessive ringing
- D) All these choices are correct
Correct Answer: A
Explanation
Automatic Notch Filters (ANFs) use digital signal processing (DSP) techniques to automatically detect and eliminate narrow-band interference, such as unmodulated carriers or heterodyne whistles. While effective for noise reduction, ANFs operate by creating a very narrow band-reject filter at the frequency of the detected interference.
Since CW signals themselves are very narrow, the primary problem that can occur when using an ANF on a CW signal is the unintended removal of the CW signal as well as the interfering carrier. If the ANF mistakenly identifies the desired CW signal as a spurious carrier, or if the CW signal is too close to the interfering carrier, the ANF’s sharp filter may notch out the desired signal, rendering the communication impossible.
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