*Question G8A01:
How is direct binary FSK modulation generated?*  

*Correct Answer is  B: By changing an oscillator’s frequency directly with a digital control signal*  

### AI Response: (may contain errors)  

Direct binary Frequency Shift Keying (FSK) modulation is a method used to transmit digital data by varying the frequency of a carrier wave. Here's why the correct answer is correct and why the other choices are incorrect:

1. **Correct Answer: B - By changing an oscillator’s frequency directly with a digital control signal**

   - **Explanation**: In direct binary FSK, the frequency of the carrier wave is shifted between two distinct frequencies. These frequencies represent binary '0' and '1'. This is achieved by directly controlling the frequency of an oscillator with a digital signal. The digital control signal determines which frequency the oscillator should output, thus encoding the binary data.

2. **Why the other choices are incorrect**:

   - **Choice A: By keying an FM transmitter with a sub-audible tone**
     - **Explanation**: This describes a method more akin to tone squelch or CTCSS, which is used for signaling and not for binary data transmission. It does not involve direct frequency changes based on digital data.

   - **Choice C: By using a transceiver’s computer data interface protocol to change frequencies**
     - **Explanation**: While a computer interface can control a transceiver, this method does not describe direct binary FSK modulation. It involves more complex protocols and is not a direct frequency shift based on binary data.

   - **Choice D: By reconfiguring the CW keying input to act as a tone generator**
     - **Explanation**: This option suggests using a CW (Continuous Wave) keying input for tone generation, which is unrelated to FSK. CW is typically used for Morse code, not for frequency shift keying.

In summary, direct binary FSK modulation involves directly altering the frequency of an oscillator with a digital signal, which is why option B is the correct choice.