Ham Radio Technician Test Radio Wave Propagation & Modulation 3 — Questions and Answers
Question 1: What happens to the MUF (Maximum Usable Frequency) when solar activity decreases?
- MUF increases because the ionosphere is less disturbed
- MUF decreases because the ionosphere is less ionized (Correct answer)
- MUF stays the same regardless of solar activity
- MUF only changes at night
Correct answer: MUF decreases because the ionosphere is less ionized
Lower solar activity means less UV radiation ionizing the ionosphere, which reduces the MUF and limits long-distance HF propagation to lower frequencies.
Question 2: What is the purpose of a CTCSS tone on an FM transmission?
- To increase transmitter power
- To access repeaters or squelch a receiver only when the correct tone is present (Correct answer)
- To modulate the carrier for better audio quality
- To identify the transmitting station automatically
Correct answer: To access repeaters or squelch a receiver only when the correct tone is present
CTCSS (Continuous Tone-Coded Squelch System) is a subaudible tone transmitted to open a repeater's receiver or a radio's squelch only when the matching tone is present.
Question 3: Why does AM voice occupy more bandwidth than SSB?
- AM uses a higher carrier frequency
- AM transmits both sidebands plus a full carrier, while SSB suppresses one sideband and the carrier (Correct answer)
- AM modulates at a higher audio frequency
- AM requires a larger antenna
Correct answer: AM transmits both sidebands plus a full carrier, while SSB suppresses one sideband and the carrier
A standard AM signal transmits an upper sideband, a lower sideband, and a carrier, using roughly twice the bandwidth of SSB which transmits only one sideband.
Question 4: What is multipath propagation?
- Signals that travel through multiple ionospheric layers simultaneously
- Signals arriving at a receiver via two or more different paths, causing interference (Correct answer)
- Using two separate antennas to send the same signal
- A propagation mode that works on multiple frequency bands
Correct answer: Signals arriving at a receiver via two or more different paths, causing interference
Multipath occurs when a transmitted signal reaches the receiver by two or more different routes (e.g., direct path plus a reflected path), which can cause phase cancellation and fading.
Question 5: At what time of day is the D layer absorption of HF signals greatest?
- Just before sunrise
- Local noon when solar radiation is strongest (Correct answer)
- Midnight when the ionosphere is most stable
- Early morning when the E layer is active
Correct answer: Local noon when solar radiation is strongest
The D layer is most heavily ionized at local noon when the sun is at its highest and solar UV radiation is most intense, causing maximum absorption of lower HF frequencies.
Question 6: What does the term 'skip zone' mean in HF propagation?
- The area where ground wave coverage ends and sky wave coverage begins, with no coverage in between (Correct answer)
- A region of heavy ionospheric absorption
- The distance between two ionospheric reflection points
- The area covered by tropospheric ducting
Correct answer: The area where ground wave coverage ends and sky wave coverage begins, with no coverage in between
The skip zone is the region between the farthest reach of ground wave propagation and the nearest point where sky wave signals return to Earth, resulting in no reception of a given station.
Question 7: Which emission type is most efficient for weak-signal HF communication when bandwidth is limited?
- AM double-sideband full carrier
- Frequency modulation (FM)
- Single sideband suppressed carrier (SSB) (Correct answer)
- On-off keying (OOK)
Correct answer: Single sideband suppressed carrier (SSB)
SSB concentrates all transmitter power into a single sideband with no wasted carrier or duplicate sideband, making it more efficient and narrower than AM or FM for voice.
Ham Radio Technician Test Radio Wave Propagation & Modulation 3
What happens to the MUF (Maximum Usable Frequency) when solar activity decreases?