Ham Radio Technician Test Radio Wave Propagation & Modulation 5 — Questions and Answers
Question 1: What is the primary advantage of using upper sideband (USB) vs. lower sideband (LSB) on HF?
- USB provides better range on all frequencies
- By convention, USB is used above 10 MHz and LSB below 10 MHz, with no technical quality difference (Correct answer)
- USB eliminates interference from the carrier
- LSB is prohibited on amateur frequencies above 10 MHz
Correct answer: By convention, USB is used above 10 MHz and LSB below 10 MHz, with no technical quality difference
There is no technical difference in quality — the convention of USB above 10 MHz and LSB below is a universally agreed amateur radio practice for interoperability.
Question 2: What is tropospheric scatter propagation?
- Refraction of signals by the troposphere's temperature layers
- Scattering of signals by turbulence and irregularities in the troposphere, allowing beyond-horizon VHF/UHF communication (Correct answer)
- Reflection of signals off mountain ranges
- Sky wave propagation through the troposhere
Correct answer: Scattering of signals by turbulence and irregularities in the troposphere, allowing beyond-horizon VHF/UHF communication
Troposcatter uses small irregularities in the troposphere to scatter some signal energy forward, enabling VHF and UHF communication beyond the horizon — typically 100–600 miles.
Question 3: What causes the 'gray line' to be a favorable time for long-distance propagation on HF?
- Atmospheric pressure is lowest at dawn and dusk, reducing signal absorption
- The D layer is absent while the F layer remains ionized, reducing absorption while maintaining refraction (Correct answer)
- The ionosphere is most stable along the terminator line
- Solar wind is deflected away from the gray line
Correct answer: The D layer is absent while the F layer remains ionized, reducing absorption while maintaining refraction
Along the terminator (gray line between day and night), the absorbing D layer rapidly disappears while the F layer remains ionized, creating a brief window of low-loss HF propagation.
Question 4: How does phase modulation (PM) differ from frequency modulation (FM)?
- PM varies the carrier amplitude; FM varies the carrier frequency
- PM varies the phase of the carrier; FM varies the frequency — PM deviation is proportional to modulating frequency, FM is proportional to amplitude (Correct answer)
- PM is only used for digital signals; FM is only for voice
- There is no practical difference between PM and FM
Correct answer: PM varies the phase of the carrier; FM varies the frequency — PM deviation is proportional to modulating frequency, FM is proportional to amplitude
In PM, phase deviation is proportional to the instantaneous amplitude of the modulating signal; in FM, frequency deviation is proportional to amplitude — but at a given frequency, PM deviation also rises with modulating frequency.
Question 5: What is the typical maximum distance for reliable ground wave propagation at 3.5 MHz (80 meters)?
- 10–20 miles
- 50–100 miles
- 300–500 miles (Correct answer)
- 1,000–2,000 miles
Correct answer: 300–500 miles
At 3.5 MHz, ground wave propagation typically covers 300–500 miles over average terrain, making 80 meters useful for regional communication without relying on the ionosphere.
Question 6: What is meant by the term 'propagation path loss'?
- Loss caused only by ionospheric absorption
- The reduction in signal strength as a radio wave travels from transmitter to receiver (Correct answer)
- The loss of signal when transmitted through a coaxial cable
- Attenuation caused by antenna mismatch
Correct answer: The reduction in signal strength as a radio wave travels from transmitter to receiver
Path loss refers to the total reduction in signal power between the transmitter and receiver due to spreading of the wave, absorption, and other environmental factors.
Question 7: Which phenomenon explains why 6-meter (50 MHz) signals can sometimes propagate across the entire continental US without the F layer?
- Tropospheric ducting
- Meteor scatter
- Sporadic-E propagation (Correct answer)
- Ground wave
Correct answer: Sporadic-E propagation
Sporadic-E (Es) patches of dense ionization in the E layer can refract 6-meter signals over distances of 500–1,500 miles, occasionally linking stations across the continent.
Ham Radio Technician Test Radio Wave Propagation & Modulation 5
What is the primary advantage of using upper sideband (USB) vs. lower sideband (LSB) on HF?