Max power transee ez1/9/2023 An impedance mismatch at any point in the entire free space→antenna→feed line→receiver system will reflect some of the signal back out, making the received signal that much weaker. In receivers, the incoming signal has already been traveling when it gets to the antenna and there is no active device driving it. The output device is interacting instantaneously with (the matching network connected to) the 50 Ω line, and so the output can be designed as a lumped circuit driving a 50 Ω resistive load without transmission-line effects.Īnother point is that this reasoning does not apply to receivers. ![]() At the transmitter, there is not yet any length for the reflection to travel over, so there cannot be any phase shift. This is true - everywhere but at the transmitter/amplifier output! What we want to avoid is reflections that cause phase shifts. You may wonder: but don't we always make sure the antenna system is 50 Ω (or whatever impedance) everywhere? Aren't impedance mismatches really bad? The maximum practical power is achieved at the point where the transmitter has reached its heat-dissipation limit (would overheat) or its circuits can no longer deliver more current to the output (would distort). A low impedance works fine for this purpose. In a radio transmitter or amplifier, we design the output to operate efficiently, sending RF to the antenna and not heating itself up unnecessarily. ![]() ![]() If you apply the maximum power transfer theorem to a typical solid-state RF transmitter, it will overheat (or reduce output to protect itself). It does not tell you that the source will survive this treatment, and it does not tell you how to best design a source given a load. The maximum power transfer theorem tells you how to design a load to extract the maximum possible power from a given source.
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