Question E2B09:
What kind of receiver can be used to receive and decode SSTV using the Digital Radio Mondiale (DRM) protocol?  

Choices:  
A: CDMA  
B: AREDN  
C: AM  
D: SSB    

Correct Answer is  D: SSB  

To receive and decode DRM-based “digital SSTV” (e.g., EasyPal/HamDRM), you use a standard SSB receiver and feed the audio to a computer decoder.

Why D (SSB) is correct:
- DRM-based ham image modes are transmitted as a digital audio signal that fits inside the normal SSB audio passband (about 2.3–2.5 kHz).
- An SSB receiver preserves the amplitude and phase of the complex audio needed for DRM’s COFDM, allowing software to decode the image.

Why the others are incorrect:
- A: CDMA — A cellular spread-spectrum system, not a ham radio receiver mode and not used for DRM/SSTV on HF.
- B: AREDN — A mesh networking firmware for 2.4/5 GHz Wi‑Fi hardware, not an HF receiver mode.
- C: AM — Envelope detection distorts complex DRM signals and typical AM audio bandwidth/filters won’t pass the required baseband cleanly.

Useful rules of thumb:
- Any soundcard digital mode that fits in the SSB passband can be received with an SSB receiver and decoded in software.
- Use a wide SSB filter: about $2.4$–$3.0$ kHz for ham-DRM image modes.
- For tuning audio-based modes over SSB:
  - USB: $f_{RF} = f_{VFO} + f_{audio}$
  - LSB: $f_{RF} = f_{VFO} - f_{audio}$
- Disable/avoid processing that distorts the audio path (AGC fast, NR, NB, notch filters, speech processing).