Question E3C09:
What type of data is reported by amateur radio propagation reporting networks?  

Choices:  
A: Solar flux  
B: Electric field intensity  
C: Magnetic declination  
D: Digital-mode and CW signals    

Correct Answer is  D: Digital-mode and CW signals  

To understand “propagation reporting networks,” think WSPRnet, PSK Reporter, and the Reverse Beacon Network (RBN). These systems automatically “spot” stations they decode and publish who-heard-whom, on what frequency, when, and with what signal report.

Why D is correct (Digital-mode and CW signals):
- Networks like:
  - WSPRnet: reports weak-signal digital mode spots (callsign, grid, SNR, frequency, time).
  - PSK Reporter: reports many digital modes (e.g., FT8, PSK31, JT65).
  - Reverse Beacon Network (RBN): reports CW (and some digital like RTTY) spots via skimmer receivers.
- These are used by hams to observe real-world propagation paths in near real time.

Why the others are incorrect:
- A: Solar flux — The 10.7 cm Solar Flux Index (SFI) is measured by observatories (e.g., NRC/NOAA), not by ham spotting networks.
- B: Electric field intensity — Not what these networks measure or report; they decode signals and log spots, not absolute field strength in V/m.
- C: Magnetic declination — A geophysical quantity (angle between magnetic and true north), unrelated to what these ham networks report.

Useful rules of thumb and formulas:
- Reported signal quality is often in dB SNR. By definition:
  $$\mathrm{SNR_{dB}} = 10 \log_{10}\!\left(\frac{P_S}{P_N}\right)$$
- Noise power scales with measurement bandwidth $B$:
  $$N \propto B \quad \Rightarrow \quad \Delta \mathrm{SNR_{dB}} = 10 \log_{10}\!\left(\frac{B_1}{B_2}\right)$$
  Example: If SNR is referenced to $B_1 = 2500\,\text{Hz}$ (typical for WSPR/FT8 reporting) and you compare to a narrower bandwidth $B_2$, SNR increases by $10\log_{10}(2500/B_2)$ dB.
- Typical decode thresholds (approximate, in 2.5 kHz reference):
  - WSPR: around −28 dB
  - FT8: around −24 dB
  - CW skimmers: higher SNR needed than the above ultra-weak digital modes

Bottom line: Propagation reporting networks crowdsource reception reports (spots) of digital and CW signals, enabling hams to see which paths are open, when, and on what bands.