Amateur Extra E4D: Dynamic range, intermod and link budgets
These are the 13 official questions in group E4D of the 2024–2028 Amateur Extra question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
Learn E4D step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.
- E4D01Question 1
What is meant by the blocking dynamic range of a receiver?
- AThe difference in dB between the noise floor and the level of an incoming signal that will cause 1 dB of gain compression Correct
- BThe minimum difference in dB between the levels of two FM signals that will cause one signal to block the other
- CThe difference in dB between the noise floor and the third-order intercept point
- DThe minimum difference in dB between two signals which produce third-order intermodulation products greater than the noise floor
Why: Blocking dynamic range runs from the noise floor to the signal level that causes 1 dB compression.
- E4D02Question 2
Which of the following describes problems caused by poor dynamic range in a receiver?
- ASpurious signals caused by cross modulation and desensitization from strong adjacent signals Correct
- BOscillator instability requiring frequent retuning and loss of ability to recover the opposite sideband
- CPoor weak signal reception caused by insufficient local oscillator injection
- DOscillator instability and severe audio distortion of all but the strongest received signals
Why: Poor dynamic range causes cross-modulation and desensitization.
- E4D03Question 3
What creates intermodulation interference between two repeaters in close proximity?
- AThe output signals cause feedback in the final amplifier of one or both transmitters
- BThe output signals mix in the final amplifier of one or both transmitters Correct
- CThe input frequencies are harmonically related
- DThe output frequencies are harmonically related
Why: The repeaters' signals mix in a transmitter's final amplifier.
- E4D04Question 4
Which of the following is used to reduce or eliminate intermodulation interference in a repeater caused by a nearby transmitter?
- AA band-pass filter in the feed line between the transmitter and receiver
- BA properly terminated circulator at the output of the repeater’s transmitter Correct
- CUtilizing a Class C final amplifier
- DUtilizing a Class D final amplifier
Why: A properly terminated circulator on the transmitter output blocks the other signal.
- E4D06Question 5
What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency?
- AReciprocal mixing
- BQuieting
- CDesensitization Correct
- DCross modulation interference
Why: Desensitization is reduced sensitivity from a strong nearby signal.
- E4D07Question 6
Which of the following reduces the likelihood of receiver desensitization?
- AInsert attenuation before the first RF stage Correct
- BRaise the receiver’s IF frequency
- CIncrease the receiver’s front-end gain
- DSwitch from fast AGC to slow AGC
Why: Attenuation before the first RF stage reduces desense.
- E4D08Question 7
What causes intermodulation in an electronic circuit?
- ANegative feedback
- BLack of neutralization
- CNonlinear circuits or devices Correct
- DPositive feedback
Why: Nonlinear circuits or devices create intermodulation.
- E4D09Question 8
What is the purpose of the preselector in a communications receiver?
- ATo store frequencies that are often used
- BTo provide broadband attenuation before the first RF stage to prevent intermodulation
- CTo increase the rejection of signals outside the band being received Correct
- DTo allow selection of the optimum RF amplifier device
Why: A preselector rejects signals outside the band you're receiving.
- E4D10Question 9
What does a third-order intercept level of 40 dBm mean with respect to receiver performance?
- ASignals less than 40 dBm will not generate audible third-order intermodulation products
- BThe receiver can tolerate signals up to 40 dB above the noise floor without producing third-order intermodulation products
- CA pair of 40 dBm input signals will theoretically generate a third-order intermodulation product that has the same output amplitude as either of the input signals Correct
- DA pair of 1 mW input signals will produce a third-order intermodulation product that is 40 dB stronger than the input signal
Why: At the intercept point, the third-order product would be as strong as the inputs.
- E4D11Question 10
Why are odd-order intermodulation products, created within a receiver, of particular interest compared to other products?
- AOdd-order products of two signals in the band being received are also likely to be within the band Correct
- BOdd-order products are more likely to overload the IF filters
- COdd-order products are an indication of poor image rejection
- DOdd-order intermodulation produces three products for every input signal within the band of interest
Why: Odd-order products from in-band signals land in-band too.
- E4D12Question 11
What is the link margin in a system with a transmit power level of 10 W (+40 dBm), a system antenna gain of 10 dBi, a cable loss of 3 dB, a path loss of 136 dB, a receiver minimum discernable signal of -103 dBm, and a required signal-to-noise ratio of 6 dB?
- A-8dB
- B-14dB
- C+8dB Correct
- D+14dB
Why: Received: 40 + 10 − 3 − 136 = −89 dBm. Needed: −103 + 6 = −97 dBm. Margin: +8 dB.
- E4D13Question 12
What is the received signal level with a transmit power of 10 W (+40 dBm), a transmit antenna gain of 6 dBi, a receive antenna gain of 3 dBi, and a path loss of 100 dB?
- A-51 dBm Correct
- B-54 dBm
- C-57 dBm
- D-60 dBm
Why: 40 + 6 + 3 − 100 = −51 dBm.
- E4D14Question 13
What power level does a receiver minimum discernible signal of -100 dBm represent?
- A100 microwatts
- B0.1 microwatt
- C0.001 microwatts
- D0.1 picowatts Correct
Why: −100 dBm = 10⁻¹³ W = 0.1 picowatts.
Learn E4D step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.