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NEW Extra Class Exam Question Pool

effective 7/01/2012 thru 6/30/2016

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E4D-2012: Receiver performance characteristics, blocking dynamic range, intermodulation and cross-modulation interference; 3rd order intercept; desensitization; preselection

E4D01-2012: What is meant by the blocking dynamic range of a receiver?

The difference in dB between the noise floor and the level of an incoming signal which will cause 1 dB of gain compression

The minimum difference in dB between the levels of two FM signals which will cause one signal to block the other

The difference in dB between the noise floor and the third order intercept point

The minimum difference in dB between two signals which produce third order intermodulation products greater than the noise floor



E4D02-2012: Which of the following describes two problems caused by poor dynamic range in a communications receiver?

Cross-modulation of the desired signal and desensitization from strong adjacent signals

Oscillator instability requiring frequent retuning and loss of ability to recover the opposite sideband

Cross-modulation of the desired signal and insufficient audio power to operate the speaker

Oscillator instability and severe audio distortion of all but the strongest received signals



E4D03-2012: How can intermodulation interference between two repeaters occur?

When the repeaters are in close proximity and the signals mix in the final amplifier of one or both transmitters

When the repeaters are in close proximity and the signals cause feedback in the final amplifier of one or both transmitters

When the signals from the transmitters are reflected out of phase from airplanes passing overhead

When the signals from the transmitters are reflected in phase from airplanes passing overhead



E4D04-2012: Which of the following may reduce or eliminate intermodulation interference in a repeater caused by another transmitter operating in close proximity?

A properly terminated circulator at the output of the transmitter

A band-pass filter in the feed line between the transmitter and receiver

A Class C final amplifier

A Class D final amplifier



E4D05-2012: What transmitter frequencies would cause an intermodulation-product signal in a receiver tuned to 146.70 MHz when a nearby station transmits on 146.52 MHz?

146.34 MHz and 146.61 MHz

146.88 MHz and 146.34 MHz

146.10 MHz and 147.30 MHz

173.35 MHz and 139.40 MHz



E4D06-2012: What is the term for unwanted signals generated by the mixing of two or more signals?

Intermodulation interference

Amplifier desensitization

Neutralization

Adjacent channel interference



E4D07-2012: Which of the following describes the most significant effect of an off-frequency signal when it is causing cross-modulation interference to a desired signal?

The off-frequency unwanted signal is heard in addition to the desired signal

A large increase in background noise

A reduction in apparent signal strength

The desired signal can no longer be heard



E4D08-2012: What causes intermodulation in an electronic circuit?

Nonlinear circuits or devices

Too little gain

Lack of neutralization

Positive feedback



E4D09-2012: What is the purpose of the preselector in a communications receiver?

To increase rejection of unwanted signals

To store often-used frequencies

To provide a range of AGC time constants

To allow selection of the optimum RF amplifier device



E4D10-2012: What does a third-order intercept level of 40 dBm mean with respect to receiver performance?

A pair of 40 dBm signals will theoretically generate a third-order intermodulation product with the same level as the input signals

Signals less than 40 dBm will not generate audible third-order intermodulation products

The receiver can tolerate signals up to 40 dB above the noise floor without producing third-order intermodulation products

A pair of 1 mW input signals will produce a third-order intermodulation product which is 40 dB stronger than the input signal



E4D11-2012: Why are third-order intermodulation products created within a receiver of particular interest compared to other products?

The third-order product of two signals which are in the band of interest is also likely to be within the band

The third-order intercept is much higher than other orders

Third-order products are an indication of poor image rejection

Third-order intermodulation produces three products for every input signal within the band of interest



E4D12-2012: What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency?

Desensitization

Quieting

Cross-modulation interference

Squelch gain rollback



E4D13-2012: Which of the following can cause receiver desensitization?

Strong adjacent-channel signals

Audio gain adjusted too low

Audio bias adjusted too high

Squelch gain misadjusted



E4D14-2012: Which of the following is a way to reduce the likelihood of receiver desensitization?

Decrease the RF bandwidth of the receiver

Raise the receiver IF frequency

Increase the receiver front end gain

Switch from fast AGC to slow AGC





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E4C-2012: Receiver performance characteristics, phase noise, capture effect, noise floor, image rejection, MDS, signal-to-noise-ratio; selectivity
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E4E-2012: Noise suppression: system noise; electrical appliance noise; line noise; locating noise sources; DSP noise reduction; noise blankers
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