Ham Radio General Class Test Radio Wave Propagation 5 — Questions and Answers
Question 1: What is 'antenna reciprocity' as it applies to propagation path selection?
- An antenna that transmits in all directions equally well also receives equally in all directions
- A directional antenna used for reception will have the same pattern for transmission, so the best transmit bearing is also the best receive bearing (Correct answer)
- Antennas can only be reciprocal below 30 MHz
- Reciprocity means doubling transmit power doubles receive signal strength
Correct answer: A directional antenna used for reception will have the same pattern for transmission, so the best transmit bearing is also the best receive bearing
By the reciprocity principle, an antenna's transmit and receive patterns are identical, so pointing a beam for the strongest received signal is also optimal for transmitting.
Question 2: During a geomagnetic storm, which HF bands are typically most affected?
- The lower HF bands (40, 80, 160 meters) are totally unusable while higher bands remain open
- The higher HF bands (15, 10 meters) suffer the worst degradation at high latitudes while lower bands may still work (Correct answer)
- All bands are equally and uniformly degraded
- Only the 60-meter band is affected because of its government allocations
Correct answer: The higher HF bands (15, 10 meters) suffer the worst degradation at high latitudes while lower bands may still work
Geomagnetic storms raise the LUF and lower the MUF, most severely impacting high-latitude paths on the upper HF bands while lower bands often remain workable.
Question 3: What is the approximate maximum distance for reliable ground-wave propagation on 40 meters?
- 50 km
- 200-500 km (Correct answer)
- 1,500 km
- 5,000 km
Correct answer: 200-500 km
Ground-wave propagation on 40 meters can reach roughly 200-500 km over average terrain; at lower frequencies like 160 meters this range extends farther.
Question 4: What is 'chordal hop' propagation?
- A single very low-angle sky-wave hop that stays within the ionosphere between two points without touching Earth, enabling very long paths with low loss (Correct answer)
- A short-skip condition on 10 meters caused by Es
- Multi-hop propagation that bounces between two ionospheric layers simultaneously
- Ground-wave propagation along a great-circle chord
Correct answer: A single very low-angle sky-wave hop that stays within the ionosphere between two points without touching Earth, enabling very long paths with low loss
In chordal hop, signals travel within the ionosphere from one point to another without returning to Earth, reducing ground-reflection losses and enabling very efficient long-distance paths.
Question 5: How does sea-water ground conductivity compare to average soil for ground-wave propagation?
- Sea water is a poor conductor and degrades ground-wave propagation compared to dry soil
- Sea water is an excellent conductor and dramatically extends ground-wave range compared to average soil (Correct answer)
- Sea water and dry soil have nearly identical effects on ground-wave propagation
- Sea water improves propagation only above 30 MHz
Correct answer: Sea water is an excellent conductor and dramatically extends ground-wave range compared to average soil
Sea water has very high conductivity (~5 S/m vs ~0.005 S/m for average soil), which greatly reduces ground-wave attenuation and extends range, especially on lower HF and MF bands.
Question 6: What is the significance of the 'critical frequency' (fo) of the ionosphere?
- It is the lowest frequency that can be used for ground-wave propagation
- It is the highest frequency that is refracted back to Earth at vertical incidence; it sets the baseline for calculating MUF at any angle (Correct answer)
- It is the frequency at which the D layer begins to absorb signals
- It is the center frequency of the 40-meter amateur band
Correct answer: It is the highest frequency that is refracted back to Earth at vertical incidence; it sets the baseline for calculating MUF at any angle
The critical frequency is measured by vertical-incidence sounders (ionosondes) and represents the highest frequency returned straight down; MUF for any oblique path is derived from it using a secant factor.
Question 7: What propagation characteristic is most responsible for the 'dead band' phenomenon sometimes observed on 10 meters?
- Excessive noise from solar flares permanently silences the band
- When solar flux is low, the MUF rarely rises above 28 MHz, leaving 10 meters with neither reliable skip nor adequate ground-wave range (Correct answer)
- D-layer absorption is strongest on 10 meters during solar minimum
- 10 meters is allocated to government use during solar minimum, reducing amateur activity
Correct answer: When solar flux is low, the MUF rarely rises above 28 MHz, leaving 10 meters with neither reliable skip nor adequate ground-wave range
At solar minimum, the MUF often stays below 28 MHz, so 10 meters has no usable sky-wave propagation and ground-wave range is very limited, making the band appear dead.
Ham Radio General Class Test Radio Wave Propagation 5
What is 'antenna reciprocity' as it applies to propagation path selection?