Try a higher frequency
Try the other sideband
Try a different antenna polarization
Try a different frequency shift

It disrupts higher-latitude paths more than lower-latitude paths
It disrupts signals on lower frequencies more than those on higher frequencies
It disrupts communications via satellite more than direct communications
None, because only areas on the night side of the Earth are affected

28 days
Several hours depending on the position of the Earth in its orbit
Approximately 8 minutes
20 to 40 hours after the radiation reaches the Earth

The density of the sun's magnetic field
The radio energy emitted by the sun
The number of sunspots on the side of the sun facing the Earth
A measure of the tilt of the Earth's ionosphere on the side toward the sun

A measure of the highest frequency that is useful for ionospheric propagation between two points on the Earth
A count of sunspots which is adjusted for solar emissions
Another name for the American sunspot number
A measure of solar activity at 10.7 cm

A sudden drop in the solar-flux index
A shifting of the Earth's magnetic pole
Ripples in the ionosphere
A significant change in the Earth's magnetic field over a short period of time

Those greater than 45 degrees North or South latitude
Those between 5 and 45 degrees North or South latitude
Those at or very near to the equator
All paths are affected equally

Improved high-latitude HF propagation
Degraded high-latitude HF propagation
Improved ground-wave propagation
Improved chances of UHF ducting

High-frequency radio signals become weak and distorted
Frequencies above 300 MHz become usable for long-distance communication
Long-distance communication in the upper HF and lower VHF range is enhanced
Long-distance communication in the upper HF and lower VHF range is diminished

A measure of solar activity based on counting sunspots and sunspot groups
A 3 digit identifier which is used to track individual sunspots
A measure of the radio flux from the sun measured at 10.7 cm
A measure of the sunspot count based on radio flux measurements

Approximately 8 minutes
Between 20 and 40 hours
Approximately 28 days
Approximately 11 years

An index of the relative position of sunspots on the surface of the sun
A measure of the short term stability of the Earth's magnetic field
A measure of the stability of the sun's magnetic field
An index of solar radio flux measured at Boulder, Colorado

An index of the relative position of sunspots on the surface of the sun
The amount of polarization of the sun's electric field
An indicator of the long term stability of the Earth's geomagnetic field
An index of solar radio flux measured at Boulder, Colorado

HF communications are improved
HF communications are disturbed
VHF/UHF ducting is improved
VHF/UHF ducting is disturbed

28 days
14 days
The effect is instantaneous
20 to 40 hours

Aurora that can reflect VHF signals
Higher signal strength for HF signals passing through the polar regions
Improved HF long path propagation
Reduced long delayed echoes

At the summer solstice
Only at the maximum point of the solar cycle
Only at the minimum point of the solar cycle
At any point in the solar cycle

7 days later
14 days later
28 days later
90 days later

Frequencies below 3.5 MHz
Frequencies near 3.5 MHz
Frequencies at or above 10 MHz
Frequencies above 20 MHz

10 meters
15 meters
20 meters
40 meters

80 meters
40 meters
20 meters
2 meters

Select a frequency just below the MUF
Select a frequency just above the LUF
Select a frequency just below the critical frequency
Select a frequency just above the critical frequency

Listen for signals on a 28 MHz international beacon
Send a series of dots on the 28 MHz band and listen for echoes from your signal
Check the strength of TV signals from Western Europe
Listen to WWV propagation signals on the 28 MHz band

They are bent back to the Earth
They pass through the ionosphere
They are completely absorbed by the ionosphere
They are bent and trapped in the ionosphere to circle the Earth

They are bent back to the Earth
They pass through the ionosphere
They are completely absorbed by the ionosphere
They are bent and trapped in the ionosphere to circle the Earth

The Lowest Usable Frequency for communications between two points
The Longest Universal Function for communications between two points
The Lowest Usable Frequency during a 24 hour period
The Longest Universal Function during a 24 hour period

The Minimum Usable Frequency for communications between two points
The Maximum Usable Frequency for communications between two points
The Minimum Usable Frequency during a 24 hour period
The Maximum Usable Frequency during a 24 hour period

180 miles
1,200 miles
2,500 miles
12,000 miles

180 miles
1,200 miles
2,500 miles
12,000 miles

No HF radio frequency will support communications over the path
HF communications over the path are enhanced at the frequency where the LUF and MUF are the same
Double hop propagation along the path is more common
Propagation over the path on all HF frequencies is enhanced

Path distance and location
Time of day and season
Solar radiation and ionospheric disturbance
All of these choices are correct

Periodic fading approximately every 10 seconds
Signal strength increased by 3 dB
The signal will be cancelled causing severe attenuation
A well-defined echo can be heard

Short hop sky-wave propagation on the 10 meter band
Long hop sky-wave propagation on the 10 meter band
Severe attenuation of signals on the 10 meter band
Long delayed echoes on the 10 meter band

The D layer
The E layer
The F1 layer
The F2 layer

At noon during the summer
At midnight during the summer
At dusk in the spring and fall
At noon during the winter

Because it is the densest ionospheric layer
Because it does not absorb radio waves as much as other ionospheric regions
Because it is the highest ionospheric region
All of these choices are correct

The long path azimuth of a distant station
The short path azimuth of a distant station
The lowest takeoff angle that will return a radio wave to the Earth under specific ionospheric conditions
The highest takeoff angle that will return a radio wave to the Earth under specific ionospheric conditions

The F layer absorbs these frequencies during daylight hours
The F layer is unstable during daylight hours
The D layer absorbs these frequencies during daylight hours
The E layer is unstable during daylight hours

They have high intelligibility
They have a wavering sound
They have very large swings in signal strength
All of these choices are correct

The ionospheric layer involved is unstable
Ground waves are absorbing much of the signal
The E-region is not present
Energy is scattered into the skip zone through several radio wave paths

Only a small part of the signal energy is scattered into the skip zone
Signals are scattered from the troposphere which is not a good reflector
Propagation is through ground waves which absorb most of the signal energy
Propagations is through ducts in F region which absorb most of the energy

Ground wave
Scatter
Sporadic-E skip
Short-path skip

The communication is during a sunspot maximum
The communication is during a sudden ionospheric disturbance
The signal is heard on a frequency below the maximum usable frequency
The signal is heard on a frequency above the maximum usable frequency

Absorption will be minimum
Absorption is greater for vertically polarized waves
Absorption approaches maximum
Absorption is greater for horizontally polarized waves

The F2 layer
The F1 layer
The E layer
The D layer

Propagation near the MUF
Short distance HF propagation using high elevation angles
Long path HF propagation at sunrise and sunset
Double hop propagation near the LUF

A vertical antenna
A horizontal dipole placed between 1/8 and 1/4 wavelength above the ground
A left-hand circularly polarized antenna
A right-hand circularly polarized antenna