Question E2B07:
Which types of modulation are used for amateur television DVB-T signals?  

Choices:  
A: FM and FSK  
B: QAM and QPSK  
C: AM and OOK  
D: All these choices are correct    

Correct Answer is  B: QAM and QPSK  

Answer: B — QAM and QPSK

1) Why B is correct
- DVB-T (Digital Video Broadcasting–Terrestrial) uses COFDM, where each OFDM subcarrier is digitally modulated with QPSK, 16-QAM, or 64-QAM depending on desired robustness and data rate.
- QPSK (Quadrature Phase Shift Keying) and QAM (Quadrature Amplitude Modulation) are the standard DVB-T constellation options used in amateur DVB-T as well.

2) Why the other choices are incorrect
- A: FM and FSK
  - FM is an analog modulation and not used for DVB-T.
  - FSK (frequency shift keying) is not part of the DVB-T modulation options.
- C: AM and OOK
  - AM (including vestigial sideband) was used by analog TV (e.g., NTSC), not DVB-T.
  - OOK (on-off keying) is a simple keying method (used in CW), not used in DVB-T.
- D: All these choices are correct
  - Incorrect because A and C include modulation types not used by DVB-T.

3) Useful formulas and rules of thumb
- For M-ary QAM/PSK, bits per symbol:
  $$b = \log_2 M$$
  - QPSK: $M=4 \Rightarrow b=2$
  - 16-QAM: $M=16 \Rightarrow b=4$
  - 64-QAM: $M=64 \Rightarrow b=6$
- Approximate data rate (per subcarrier set):
  $$R_b = R_s \cdot b \cdot r_c$$
  where:
  - $R_s$ = symbol rate,
  - $b$ = bits per symbol,
  - $r_c$ = FEC coding rate.
- Rule of thumb: Higher-order QAM (e.g., 64-QAM) gives higher throughput but needs higher SNR; QPSK is most robust for weak paths.