General exam: radio wave propagation
Sunspots, ionospheric layers, MUF and LUF, skip, and how HF conditions change. 37 questions, 10 at a time, starting with ones you haven't seen.
Rules to remember10 key radio wave propagation rulesShow the rules
- Ultraviolet and X-ray radiation travels at the speed of light, reaching Earth about 8 minutes after a flare. (p. 31)
- The highest HF bands need strong solar ionization, so 15, 12 and 10 meters are least reliable for DX when solar activity is low. (p. 31)
- Twenty meters is reliable enough that it usually supports worldwide daytime propagation at any point in the solar cycle. (p. 32)
- A coronal mass ejection is a cloud of particles moving much slower than light, taking about 15 hours to several days to reach Earth. (p. 33)
- The K-index measures short-term stability of Earth's geomagnetic field, updated every three hours. (p. 33)
- MUF means Maximum Usable Frequency for communication between two points. (p. 34)
- The F2 region is the highest ionospheric layer, so one F2 hop covers up to about 2,500 miles. (p. 35)
- The E region is lower than the F2 region, so a single E hop reaches only about 1,200 miles. (p. 35)
- The F2 region is the highest layer, so signals refracted there come down farther away, giving longer skip. (p. 36)
- In daylight the D region absorbs low-frequency HF and MF signals, limiting long-distance contacts on 160 through 40 meters. (p. 36)
Taken from the explanations to checked practice questions; page numbers link to the official handbook.
Sample radio wave propagation questions
1.Which of the following is a way to determine current propagation on a desired band from your station?
- ACheck the A-index
- BSend a series of dots and listen for echoes
- CUse a network of automated receiving stations on the internet to see where your transmissions are being received
- DAll these choices are correct
Show the answer
✓ C. Use a network of automated receiving stations on the internet to see where your transmissions are being received
Automated receiving networks such as reverse beacon or PSK Reporter show where your signal is actually being heard right now.
2.What is the solar flux index?
- AA measure of solar radiation with a wavelength of 10.7 centimeters
- BA measure of the highest frequency that is useful for ionospheric propagation between two points on Earth
- CAnother name for the American sunspot number
- DA count of sunspots that is adjusted for solar emissions
Show the answer
✓ A. A measure of solar radiation with a wavelength of 10.7 centimeters
The solar flux index measures solar radio energy at a 10.7 cm wavelength (2800 MHz), a daily gauge of solar activity.
3.What makes HF scatter signals often sound distorted?
- AEnergy is scattered into the skip zone through several different paths
- BThe E region is not present
- CThe ionospheric region involved is unstable
- DGround waves are absorbing much of the signal
Show the answer
✓ A. Energy is scattered into the skip zone through several different paths
Scatter energy reaches the skip zone over several paths of different lengths, which smears the signal and makes it sound distorted.
4.Why are HF scatter signals in the skip zone usually weak?
- APropagation is via ground waves, which absorb most of the signal energy
- BPropagation is via ducts in the F region, which absorb most of the energy
- CSignals are scattered from the magnetosphere, which is not a good reflector
- DOnly a small part of the signal energy is scattered into the skip zone
Show the answer
✓ D. Only a small part of the signal energy is scattered into the skip zone
Only a small fraction of the transmitted energy is scattered into the skip zone, so signals heard there are weak.