Question
What is the difference between direct FSK and audio FSK?
Answer Options
- A) Direct FSK modulates the transmitter VFO
- B) Direct FSK occupies less bandwidth
- C) Direct FSK can transmit higher baud rates
- D) All these choices are correct
Correct Answer: A
Explanation
FSK (Frequency-Shift Keying) is the modulation of a signal by shifting its frequency between two discrete values. This can be accomplished in two primary ways in an amateur radio transmitter. The distinction lies in where the modulation is applied within the radio’s circuitry.
The difference is that Direct FSK modulates the transmitter VFO (Variable Frequency Oscillator) or frequency synthesizer directly. This method bypasses the radio’s audio chain and creates a cleaner, more precise FSK signal. Conversely, Audio FSK (AFSK) involves injecting audio tones (the shifted frequencies) into the microphone input of an SSB transmitter, which then transmits the resulting sound on a suppressed carrier.
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