Question
What factors affect the bandwidth of a transmitted CW signal?
Answer Options
- A) IF bandwidth and Q
- B) Modulation index and output power
- C) Keying speed and shape factor (rise and fall time)
- D) All these choices are correct
Correct Answer: C
Explanation
Continuous Wave (\text{CW}) is a basic on/off keying (OOK) mode. While simple, the act of abruptly turning a signal on and off generates sidebands across the spectrum. The width of these sidebands determines the signal’s bandwidth and its potential to cause ‘key clicks’ or splatter on adjacent frequencies.
What affects the bandwidth of a transmitted \text{CW} signal are the keying speed (how fast the data is sent) and the shape factor (rise and fall time) of the \text{RF} envelope. Faster keying requires more bandwidth. Crucially, a sharp, instantaneous rise/fall time (a square wave pulse) generates wide sidebands (clicks), whereas a ‘soft’ shape (longer rise/fall time) minimizes the sidebands and results in a narrower, cleaner signal.
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