When specifying or designing any measurement receiver system, one should consider that the "system" will include other devices such as antennas, amplifiers, cabling, and possibly filters.Because a receiver's selectivity, the ability to select frequencies or frequency bands, is primarily a function of the receiver's tuner design, and will be chiefly dependent on the individual receiver selection, selectivity will not be specifically addressed in this text. Receiver system
sensitivity, however, presents one of the greatest difficulties, or
challenges, when designing or specifying receiver measurement systems. Therefore, the sensitivity of the two basic types of receiver systems,
one with a pre-amplifier and one without a pre-amplifier, will be addressed in some detail.
Because antennas are not perfect devices and have associated "losses," the following examples will include explanations for these error corrections. As mentioned previously, amplifiers will not only amplify the emissions being measured but they will also amplify ambient electromagnetic noise. These ambient conditions can drastically change the overall sensitivity of a measurement system. Another potential problem associated with using amplifiers is that they also generate internal electromagnetic noise. Being active devices they will introduce their own internal electromagnetic noise into the receiver system, again having an influence on the total system's noise level, thus, its sensitivity. Some corrections for the above mentioned problems are necessary to accurately calculate both the receiver's signal input sensitivity and (more importantly) the total system's ambient
sensitivity. Without knowing the total measurement system's ambient sensitivity, measurements may not be possible down to anticipated emission levels. In electromagnetic measurement systems terms such as ambient sensitivity, system sensitivity, and receiver sensitivity have been used interchangeably.
More confusing expressions commonly used are terms such as "receiver noise floor," or "system noise floor."
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