Technician exam: radio wave propagation
How VHF and UHF signals travel: line of sight, reflection, ducting, sporadic E and the ionosphere. 35 questions, 10 at a time, starting with ones you haven't seen.
Rules to remember10 key radio wave propagation rulesShow the rules
- Rain, snow and other precipitation absorb and scatter microwave signals, which can shorten range. (p. 25)
- Fog and rain absorb mainly microwave signals; at 10 and 6 meters the wavelength is long enough that they have little effect. (p. 26)
- A radio wave is made of an electric field and a magnetic field traveling together. (p. 26)
- UHF, ultra high frequency, covers 300 to 3000 MHz. (p. 27)
- HF, high frequency, covers 3 to 30 MHz. (p. 28)
- The speed of light, and of radio waves in free space, is about 300,000,000 meters per second. (p. 28)
- Sporadic E, patches of dense ionization in the E region, can suddenly carry strong 10, 6 and 2 meter signals well beyond the horizon. (p. 29)
- Tropospheric ducting traps VHF and UHF signals in layers of the lower atmosphere, regularly allowing contacts out to about 300 miles. (p. 29)
- Meteor trails reflect lower VHF best, so the 6-meter band is the most suitable for meteor scatter. (p. 29)
- The F region is ionized enough for 10 meters mainly in daylight and when sunspot activity is high, so daytime at solar peaks is best. (p. 30)
Taken from the explanations to checked practice questions; page numbers link to the official handbook.
Sample radio wave propagation questions
1.What type of propagation is responsible for allowing over-the-horizon VHF and UHF communications to ranges of approximately 300 miles on a regular basis?
- AF2 region refraction
- BTropospheric ducting
- CD region refraction
- DFaraday rotation
Show the answer
✓ B. Tropospheric ducting
Tropospheric ducting traps VHF and UHF signals in layers of the lower atmosphere, regularly allowing contacts out to about 300 miles.
2.Why are simplex UHF signals rarely heard beyond their radio horizon?
- AFCC regulations prohibit them from going more than 50 miles
- BThey are too weak to go very far
- CUHF signals are usually not propagated by the ionosphere
- DUHF signals are absorbed by the ionospheric D region
Show the answer
✓ C. UHF signals are usually not propagated by the ionosphere
UHF signals normally pass through the ionosphere instead of being bent back, so simplex UHF contacts are usually limited to about the radio horizon.
3.What is the relationship between wavelength and frequency?
- AWavelength gets shorter as frequency increases
- BWavelength and frequency increase as path length increases
- CWavelength gets longer as frequency increases
- DWavelength is constant at all frequencies
Show the answer
✓ A. Wavelength gets shorter as frequency increases
Wavelength and frequency are inversely related: as frequency goes up, wavelength gets shorter.
4.When using a directional antenna, how might your station be able to communicate with a distant repeater if buildings or obstructions are blocking the direct line of sight path?
- ATry to find a path that reflects signals to the repeater
- BTry the long path
- CIncrease the antenna SWR
- DChange from vertical to horizontal polarization
Show the answer
✓ A. Try to find a path that reflects signals to the repeater
When the direct path is blocked, aiming a directional antenna toward a building or hill that reflects your signal toward the repeater may get you through.