HAM - Radio Extra Class Test Radio Extra Class 1 — Questions and Answers
Question 1: What is the input impedance of a quarter-wavelength transmission line section terminated with a short circuit?
- 0 ohms (short circuit)
- Purely resistive and equal to the line's characteristic impedance Z0
- Infinite impedance (open circuit) (Correct answer)
- Z0 squared divided by the terminating impedance
Correct answer: Infinite impedance (open circuit)
A quarter-wave transmission line acts as an impedance inverter. A short circuit (0 Ω) at the far end appears as an open circuit (infinite impedance) at the input, and vice versa. This property is widely used in antenna matching networks and stub filters.
Question 2: Which filter design exhibits a maximally flat amplitude response throughout the passband, sacrificing roll-off steepness to eliminate ripple?
- Chebyshev Type I
- Elliptic (Cauer)
- Bessel
- Butterworth (Correct answer)
Correct answer: Butterworth
The Butterworth filter is specifically engineered for a 'maximally flat' passband — no ripple whatsoever. Chebyshev and elliptic filters achieve steeper roll-off at the cost of introducing passband or stopband ripple, while the Bessel filter prioritizes linear phase response.
Question 3: What is the lowest frequency in the 80-meter band at which an Extra class licensee may operate single-sideband phone?
- 3.525 MHz
- 3.600 MHz (Correct answer)
- 3.700 MHz
- 3.750 MHz
Correct answer: 3.600 MHz
FCC Part 97 grants Extra class licensees phone (including SSB) privileges beginning at 3.600 MHz on 80 meters, extending to 4.000 MHz. General class phone begins at 3.800 MHz, so Extra class has an additional 200 kHz of exclusive phone spectrum in the lower portion of the band.
Question 4: What does a receiver's third-order intercept point (IP3) specification describe?
- The input power at which the AGC circuit reduces gain by 3 dB
- The theoretical input power level at which third-order intermodulation products equal the fundamental signal amplitude (Correct answer)
- The frequency offset at which spurious responses are 3 dB above the noise floor
- The noise figure degradation caused by a 3 dB lossy input attenuator
Correct answer: The theoretical input power level at which third-order intermodulation products equal the fundamental signal amplitude
IP3 is a figure of merit for receiver linearity. It is the extrapolated input power where the third-order intermodulation products would theoretically reach the same level as the desired signals. A higher IP3 means the receiver handles strong nearby signals with less intermodulation distortion, which is critical in crowded band conditions.
Question 5: What is the approximate forward gain of a well-designed three-element Yagi antenna referenced to an isotropic radiator?
- 3 dBi
- 5 dBi
- 7 dBi (Correct answer)
- 14 dBi
Correct answer: 7 dBi
A three-element Yagi (driven element, reflector, and one director) typically achieves approximately 7 dBi (about 5 dBd) of forward gain. The reflector adds gain and improves front-to-back ratio, while the director narrows the forward lobe and boosts gain further.
Question 6: What propagation advantage does operating during the 'greyline' provide for HF amateur radio communication?
- The F2 layer reaches its maximum height, allowing the highest usable frequency to peak
- Sporadic-E clouds form preferentially along the terminator, enhancing 6-meter contacts
- Both ends of the path can simultaneously experience an absent D layer while the F layer remains ionized, enabling strong low-noise long-path signals (Correct answer)
- Tropospheric ducting is strongest along the day-night boundary, extending VHF range
Correct answer: Both ends of the path can simultaneously experience an absent D layer while the F layer remains ionized, enabling strong low-noise long-path signals
The greyline is the twilight terminator where day meets night. The D layer, which absorbs lower HF frequencies during daylight, is absent at twilight, while the F layer remains charged. When both the transmitting and receiving stations are simultaneously on or near the greyline, long-distance low-band propagation can be exceptionally strong with minimal absorption.
HAM - Radio Extra Class Test Radio Extra Class 1
What is the input impedance of a quarter-wavelength transmission line section terminated with a short circuit?