E4D-2012: Receiver performance characteristics, blocking dynamic range, intermodulation and cross-modulation interference; 3rd order intercept; desensitization; preselection
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
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
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
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
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
What is the term for unwanted signals generated by the mixing of two or more signals?
Adjacent channel interference
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
What causes intermodulation in an electronic circuit?
Nonlinear circuits or devices
Too little gain
Lack of neutralization
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
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
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
What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency?
Squelch gain rollback
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
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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