Question E2E01:
Which of the following types of modulation is used for data emissions below 30 MHz?  

Choices:  
A: DTMF tones modulating an FM signal  
B: FSK  
C: Pulse modulation  
D: Spread spectrum    

Correct Answer is  B: FSK  

To calculate the ERP:  
$$ERP = P_T \times G_A$$  
where:
- $P_T$ = transmitter power in watts
- $G_A$ = antenna gain (linear)

This shows how to compute the effective radiated power for the given setup.

Question E2E01:
Which of the following types of modulation is used for data emissions below 30 MHz?

Correct Answer: FSK

Explanation:

1) Why FSK is correct
- FSK (Frequency-Shift Keying) is a standard, narrowband data modulation widely used on HF (below 30 MHz).
- Classic HF data modes like RTTY use FSK (often AFSK through an SSB transmitter). These fit within typical HF bandwidth limits and are robust in fading and noise.
- Examples: RTTY at 45.45 baud with a 170 Hz shift; 300-baud packet on HF uses AFSK/FSK.

2) Why the other choices are incorrect
- A: DTMF tones modulating an FM signal
  - DTMF is a set of audio control tones, not a general-purpose data emission for HF.
  - FM is rarely used on HF (except limited 10 m segments) and is not the standard for HF data work.
- C: Pulse modulation
  - Pulse techniques (e.g., radar-like) are not typical or practical for amateur HF data communications.
- D: Spread spectrum
  - Not permitted below 222 MHz in the Amateur Service. Rule of thumb: spread spectrum is VHF/UHF and above, not HF.

3) Useful formulas and rules of thumb
- Approximate BFSK occupied bandwidth (Carson-like):
  $$B \approx 2(\Delta f + R_b)$$
  where $\Delta f$ is the frequency shift (Hz) and $R_b$ is the bit rate (bps).
- Data rate vs. symbol rate for M-ary schemes:
  $$R_b = R_s \log_2 M$$
- Common HF RTTY settings:
  - Baud rate: $R_s \approx 45.45$ baud
  - Shift: $\Delta f \approx 170$ Hz
- Rule of thumb: Below 30 MHz, use narrowband modes (CW, FSK/AFSK, PSK). Spread spectrum is not allowed below 222 MHz.