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

Geomagnetic storm intensity; values below 5 indicate good conditions

Answer

The number of sunspots visible; values above 50 indicate good conditions

Answer

Solar wind speed in km/s; values below 400 indicate stable 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

Excellent HF propagation conditions with low absorption

Answer

High solar flux improving F2-layer ionization

Answer

Favorable sporadic-E conditions on VHF bands

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

It improves F2-layer propagation for all bands above 14 MHz

Answer

It has no effect on HF propagation but enhances VHF propagation

Answer

It lowers the MUF, making lower HF bands more reliable

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

Propagation via meteor impacts on the Moon's surface, used on 70 cm and above

Answer

Propagation enhanced by meteor-induced aurora on 10 and 15 meters

Answer

A form of tropospheric scatter associated with meteor showers on 160 meters

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

Lower sunspot numbers at solar maximum reduce D-layer absorption, improving all HF bands

Answer

The solar cycle has no measurable effect on HF propagation at mid-latitudes

Answer

Solar maximum causes permanent ionospheric blackouts on frequencies above 21 MHz

Question 6

What is ionospheric absorption, and which ionospheric layer is primarily responsible for it during daylight hours?

Accepted Answer

The loss of HF signal energy in the D layer, which is most intense during daytime

Answer

Signal bending in the F2 layer that allows sky wave propagation

Answer

Reflection of signals at the E-layer boundary causing signal loss

Answer

UV-driven ionization that reduces signal strength near the magnetic poles

Question 7

What is 'backscatter' propagation and how can amateur operators use it?

Accepted Answer

Signals bounced back toward the transmitting station after scattering off the ionosphere or Earth, enabling contacts in or near the skip zone

Answer

Reflections off the Moon used for Earth-Moon-Earth (EME) contacts

Answer

VHF signals scattered by aircraft for short-range communication

Answer

Ground wave signals scattered by mountains back toward the transmitter