TABLE OF CONTENTS The most important performance characteristics of a receiver are its sensitivity and dynamic range. While these characteristics may be specified in a number of ways, the NF and the second- and third-order IPs are excellent measures that generally can be converted to any required specification for these characteristics. For a superheterodyne receiver, other important characteristics that must be carefully planned include the number, location, and strength of spurious responses; the selectivities to be available for different services; and the method of tracking RF preselector tuning to the LO frequency.
The ideal receiver would have 0-dB NF, very high IPs (30 to 50 dBm), and no spurious responses in excess of the thermal noise level in the most narrow available channel bandwidth of the receiver. Such ideals are not attainable in the physical world. The closest possible approach to their attainment, given the state of the art when the receiver is designed, would result in a cost that few if any customers would be willing to pay. Consequently, the design must effect a compromise between physics and economics. The most useful tool to help with these tradeoffs is the gain or level diagram.
A complete level diagram identifies each stage of the receiver from antenna input to baseband output. The impedance levels at various points are identified where significant; the power (or in some cases, voltage) gain of each stage is indicated; and the NF for each active stage is recorded at its prospective...
