HAM Practice Questions 3 — Questions and Answers
Question 1: What does the term 'third-order intercept point' (IP3) indicate about an RF amplifier?
- The frequency at which gain drops 3 dB
- A measure of the amplifier's linearity and resistance to intermodulation distortion (Correct answer)
- The power level at which the amplifier saturates
- The input impedance matching point
Correct answer: A measure of the amplifier's linearity and resistance to intermodulation distortion
IP3 is a theoretical extrapolation that quantifies an amplifier's linearity; a higher IP3 means less intermodulation distortion at a given input power.
Question 2: Which digital mode was specifically designed for weak-signal meteor-scatter and EME communication?
- PSK31
- RTTY
- JT65 (Correct answer)
- Olivia
Correct answer: JT65
JT65, developed by Joe Taylor K1JT, was designed for extremely weak signals and is widely used for EME (moon-bounce) and weak-signal VHF/UHF work.
Question 3: What is the relationship between skin depth and frequency in a conductor?
- Skin depth increases as frequency increases
- Skin depth decreases as frequency increases (Correct answer)
- Skin depth is independent of frequency
- Skin depth increases only above 30 MHz
Correct answer: Skin depth decreases as frequency increases
Skin depth decreases as frequency increases because the skin effect forces current to flow closer to the conductor's surface at higher frequencies.
Question 4: What is the function of a 'noise blanker' in a receiver?
- To reduce thermal noise in the IF strip
- To detect and suppress short-duration impulse noise pulses (Correct answer)
- To attenuate strong adjacent-channel signals
- To cancel common-mode interference on the antenna feedline
Correct answer: To detect and suppress short-duration impulse noise pulses
A noise blanker samples the incoming signal, detects impulse noise spikes (such as ignition noise), and briefly mutes the receiver during each pulse.
Question 5: When operating through a satellite repeater, why must operators use the minimum power necessary?
- FCC regulations require it for all satellite contacts
- Excessive power desensitizes the satellite's receiver and degrades the link for others (Correct answer)
- Strong signals cause the satellite to switch to a different transponder
- High power damages the satellite's solar panels
Correct answer: Excessive power desensitizes the satellite's receiver and degrades the link for others
Satellite linear transponders are shared resources; using excess power captures more of the transponder's dynamic range and causes AGC-driven gain reduction that affects all other users.
Question 6: In terms of feed-point impedance, how does a folded dipole differ from a standard half-wave dipole?
- The folded dipole has approximately 300 ohms impedance versus about 73 ohms for a standard dipole (Correct answer)
- The folded dipole has 50 ohms versus 73 ohms for a standard dipole
- Both have the same feed-point impedance
- The folded dipole's impedance depends entirely on wire gauge
Correct answer: The folded dipole has approximately 300 ohms impedance versus about 73 ohms for a standard dipole
A folded dipole has approximately 300 ohms feed-point impedance, which is about four times that of a standard half-wave dipole, making it a natural match for 300-ohm twinlead.
Question 7: What is the primary advantage of using a phase-locked loop (PLL) synthesizer for VFO frequency generation?
- Lower cost than LC oscillators
- Crystal-referenced frequency stability with continuous tuning (Correct answer)
- Wider bandwidth modulation capability
- Elimination of spurious harmonics
Correct answer: Crystal-referenced frequency stability with continuous tuning
A PLL synthesizer locks a voltage-controlled oscillator to a stable crystal reference, combining the frequency stability of a crystal with the continuous tuning of a VFO.
HAM Practice Questions 3
What does the term 'third-order intercept point' (IP3) indicate about an RF amplifier?