ARRL Radio Wave Propagation 3

Question 1

What does the Solar Flux Index (SFI) measure, and what value indicates good HF propagation conditions?

Accepted Answer

The Sun's radio emission at 10.7 cm wavelength; values above 150 indicate enhanced propagation

Answer

The Solar Flux Index measures the Sun's radio emission at 10.7 cm (2800 MHz); higher values (above 150 and especially above 200) indicate increased solar activity and better ionization of the F2 layer for HF propagation.

Question 2

The K-index is a measure used in amateur radio propagation forecasting. What does a high K-index (K=5 or above) indicate?

Accepted Answer

Increased geomagnetic storm activity likely disrupting HF propagation

Answer

A K-index of 5 or above indicates a geomagnetic storm, which disturbs the ionosphere and typically degrades or disrupts HF propagation, especially at higher latitudes.

Question 3

How does a major geomagnetic storm generally affect HF radio propagation?

Accepted Answer

It disrupts the ionosphere, causing HF blackouts and increased absorption especially at high latitudes

Answer

Geomagnetic storms, caused by coronal mass ejections (CMEs), disrupt the ionosphere and dramatically increase absorption, often causing HF radio blackouts that are worst at high latitudes.

Question 4

What is meteor scatter propagation, and on which bands is it most commonly used?

Accepted Answer

Propagation via meteors burning up in the E layer, most useful on 6 meters and 2 meters

Answer

Meteor scatter uses the ionized trails left by meteors burning up in the E layer (80–120 km) to reflect VHF signals; it is most commonly used on the 6-meter (50 MHz) and 2-meter (144 MHz) bands using digital modes like MSK144.

Question 5

What effect does the approximately 11-year solar cycle have on HF propagation?

Accepted Answer

Higher sunspot numbers at solar maximum increase F2-layer ionization, improving high-band HF propagation

Answer

At solar maximum, higher sunspot numbers produce more UV/X-ray radiation, increasing F2-layer ionization and raising the MUF; this makes the higher HF bands (15, 12, and 10 meters) much more productive for DX propagation.

(ARRL) American Radio Relay League Practice Test

(ARRL) American Radio Relay League Practice Test

ARRL Radio Wave Propagation 3