E4D: Receiver performance characteristics, part 2: 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 level of an incoming signal which will cause 1 dB of gain compression, and the level of the noise floor
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 types of 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, should it be transmitted
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 one or both transmitter final amplifiers
When the repeaters are in close proximity and the signals cause feedback in one or both transmitter final amplifiers
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
What is an effective way to reduce or eliminate intermodulation interference between two repeater transmitters operating in close proximity to one another?
By installing a properly terminated circulator at the output of the transmitter
By installing a band-pass filter in the feed line between the transmitter and receiver
By using a Class C final amplifier
By using a Class D final amplifier
If a receiver tuned to 146.70 MHz receives an intermodulation-product signal whenever a nearby transmitter transmits on 146.52 MHz, what are the two most likely frequencies for the other interfering signal?
146.34 MHz and 146.61 MHz
146.88 MHz and 146.34 MHz
146.10 MHz and 147.30 MHz
73.35 MHz and 239.40 MHz
If the signals of two transmitters mix together in one or both of their final amplifiers, and unwanted signals at the sum and difference frequencies of the original signals are generated, what is this called?
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 improve 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 the same output on the third order intermodulation frequency as on the input frequency
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 within a receiver of particular interest compared to other products?
The third-order product of two signals which are in the band is itself 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
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 adjusted too low
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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