Multisim 14.1 measure voltage across a resistor
The highest signal-to-noise ratio which leads to the best reception in a communications system is usually obtained under maximum power transfer conditions. An electronics engineer has to maximize the signal from a circuit and efficiency may not be of importance. Unlike in the power industry (which can control the value of R), control over the source of a received signal such as in a radio, television, or radar transmission usually does not exist. In the communications industry, signals are often faint, barely above the noise level, with powers sometimes on the order of microwatts or less. Power systems, therefore, tend to be operated under maximum efficiency conditions, with a goal of keeping the terminal voltage as constant as possible as the load varies.Īs little use as power engineers have for maximum power transfer, communication and electronics engineers live by it. Furthermore, the terminal voltage would drop to half, which by itself would be intolerable. It would require very large generators merely to dissipate the heat developed. For example, power utilities, which generate many megawatts of electric power, do not operate under maximum power transfer, as then half of the power would be dissipated at the power plant, a very uneconomical, inefficient, and undesirable condition.
When is maximum power transfer important and when is maximum efficiency important? The answer to these questions depends on the amount of power involved and the ease with which it can be generated.
Which gives the efficiency as 50%, for matched conditions, as expected 100% efficiency is obtained for internal resistance R = 0 (a very powerful source), or for R L → ∞ (no power absorbed by load). (1.42) η = P load P source = i 2 R L iV = R L R + R L