Question E3B10:
What is the effect of chordal-hop propagation?  

Choices:  
A: The signal experiences less loss compared to multi-hop propagation, which uses Earth as a reflector  
B: The MUF for chordal-hop propagation is much lower than for normal skip propagation  
C: Atmospheric noise is reduced in the direction of chordal-hop propagation  
D: Signals travel faster along ionospheric chords    

Correct Answer is  A: The signal experiences less loss compared to multi-hop propagation, which uses Earth as a reflector  

To understand chordal-hop propagation: it is HF propagation where the signal refracts between regions of the F layer and does not return to Earth between hops. This avoids ground reflections and much mid-path D/E-layer absorption.

Why A is correct (less loss than multi-hop using Earth as a reflector)
- Each ground reflection in ordinary multi-hop adds significant loss and depolarization. Over land this can be several dB per hop; even over sea it’s not zero.
- Chordal-hop paths eliminate intermediate ground bounces, so total path loss is lower and signals arrive stronger.

A simple link-budget view:
$$L_{\text{total}} \approx L_{\text{fs}} + N_g\,L_g + L_{\text{abs}}$$
- $L_{\text{fs}}$ = free-space-like spreading loss
- $N_g$ = number of ground reflections
- $L_g$ = loss per ground reflection (often 3–10 dB)
- $L_{\text{abs}}$ = ionospheric absorption (much of which is from D/E layer passes)
For chordal hop, $N_g \approx 0$ for the long middle of the path, so $L_{\text{total}}$ is reduced.

Why the other choices are incorrect
- B: “The MUF is much lower” — Incorrect. Chordal-hop often supports equal or higher usable frequencies than ordinary skip because the path stays in the F region at higher virtual heights and shallower incidence angles. A common relation is:
  $$MUF \approx f_{\text{crit}}\,\sec\theta$$
  Smaller $\theta$ (shallower incidence) increases MUF; chordal hop tends to have shallow angles.
- C: “Atmospheric noise is reduced in that direction” — Incorrect. Chordal hop does not reduce atmospheric noise; it reduces path loss. SNR may improve because the signal is stronger, not because the noise is lower.
- D: “Signals travel faster along ionospheric chords” — Incorrect. EM waves do not exceed $c$, and group velocities in the ionosphere are not faster. Any perceived improvement is from lower loss, not higher speed.

Rules of thumb
- Each ground bounce in multi-hop can cost roughly 3–10 dB; chordal hop avoids these mid-path bounces.
- Fewer hops and less D-layer traversal between bounces mean less absorption and often more stable signals (less multipath fading).
- Chordal-hop paths can span several thousand kilometers per “hop” without touching ground.