sensitivity:
The sensitivity of a radio receiver may be defined as its ability to amplify weak signals.
It is generally, defined in terms of the voltage which must be applied at receiver input terminals to provide a standard output power measured at the output terminals .
for AM broadcast receivers,several relevant quantities have been standardized. A signal modulated by a 400 Hz sine wave and modulation index of 30% is applied through standard coupling network known as a dummy antenna.
In addition to this,the loud-speaker is replaced by an equivalent load resistance and it must be equal to be equal to the standard value of 50 mW.
Sensitivity is also expressed in microvolts or in decibels below 1 volt and is measured at three points along the tuning range when a production receiver is lined up.
the sensitivity is generally quoted in terms of signal power required to produced a minimum acceptable output signal with a minimum acceptable output signal with a minimum acceptable output noise level.Few factors determining the sensitivity of a superheterodyne receiver are as under:
(i) The gain of the IF amplifiers.
(ii) The gain of the RF amplifiers.
(iii) The noise figure of the receiver.
It may be noted that the typical values of sensitivity are 150μ volt for small broadcast band receivers,and 1μV or below for high quality communication receiver in the HF band
selectivity:
The selectivity of a receiver may be defined as the ability to reject unwanted signals. It also expresses the attenuation that the receiver offers to signal at frequencies adjacent to the one to which it is tuned.In selectivity measurement,the frequency of the generators is varied to either side of the frequency to which the receiver is tuned.Naturally,the output of the receiver falls since the input frequency is not incorrect.Thus the input voltage must be increased until the output is the same as it was originally.The ratio of the voltage required of resonance to the voltage required. when the generator is tuned to the receiver's frequency it is calculated at a number of point and then plotted in decibels.
(i)Selectivity varies with receiving frequency and becomes somewhat worse when the receiving frequency is raised.
(ii)In general,it is mainly determiine by the response of the IF section,with the mixer and RF amplifier input circuits playing a small but significant part.
(iii)Selectivity is the main factor which determines the adjacent channel rejection of a receiver
The sensitivity of a radio receiver may be defined as its ability to amplify weak signals.
It is generally, defined in terms of the voltage which must be applied at receiver input terminals to provide a standard output power measured at the output terminals .
for AM broadcast receivers,several relevant quantities have been standardized. A signal modulated by a 400 Hz sine wave and modulation index of 30% is applied through standard coupling network known as a dummy antenna.
In addition to this,the loud-speaker is replaced by an equivalent load resistance and it must be equal to be equal to the standard value of 50 mW.
Sensitivity is also expressed in microvolts or in decibels below 1 volt and is measured at three points along the tuning range when a production receiver is lined up.
the sensitivity is generally quoted in terms of signal power required to produced a minimum acceptable output signal with a minimum acceptable output signal with a minimum acceptable output noise level.Few factors determining the sensitivity of a superheterodyne receiver are as under:
(i) The gain of the IF amplifiers.
(ii) The gain of the RF amplifiers.
(iii) The noise figure of the receiver.
It may be noted that the typical values of sensitivity are 150μ volt for small broadcast band receivers,and 1μV or below for high quality communication receiver in the HF band
selectivity:
The selectivity of a receiver may be defined as the ability to reject unwanted signals. It also expresses the attenuation that the receiver offers to signal at frequencies adjacent to the one to which it is tuned.In selectivity measurement,the frequency of the generators is varied to either side of the frequency to which the receiver is tuned.Naturally,the output of the receiver falls since the input frequency is not incorrect.Thus the input voltage must be increased until the output is the same as it was originally.The ratio of the voltage required of resonance to the voltage required. when the generator is tuned to the receiver's frequency it is calculated at a number of point and then plotted in decibels.
(i)Selectivity varies with receiving frequency and becomes somewhat worse when the receiving frequency is raised.
(ii)In general,it is mainly determiine by the response of the IF section,with the mixer and RF amplifier input circuits playing a small but significant part.
(iii)Selectivity is the main factor which determines the adjacent channel rejection of a receiver
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