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## Re: [Amps] Transceiver Output Impedance

 To: "amps@contesting.com" Re: [Amps] Transceiver Output Impedance "Jim Brown" Sun, 09 Mar 2008 12:56:02 -0800 mailto:amps@contesting.com>
 ```> For maximum power transfer the output impedance and the load must be the > same. NO! This is a major misunderstanding of the maximum power transfer theorem, which says that if a generator has a fixed value of resistance (that is, we can change ONLY the load resistance) AND IS LINEAR AT ALL OPERATING CONDITIONS INCLUDING LOAD VALUES, that maximum power will transferred when the resistances are equal. But power amplifiers are NOT LINEAR FOR ALL CONDITIONS -- they get very NON-LINEAR when heavily loaded (low values of load impedance), so the maximum power transfer theorem does not apply to power amps! But as Manfred correctly observes, power amplifiers are generally designed to work into impedances much larger than their own AC output impedance, become non-linear when more heavily loaded (lower impedance) and have more dissipation when more heavily loaded (it's a simple voltage divider with their own output R and the load). Now, the output Z of an RF power amp DOES include the output network, which is often a low pass filter. But we don't want those components overheating either! And has been correctly observed, the response of that network, like all passive networks, depends on the values of driving source impedance and load impedance. That is, the network will be designed to work with the actual output Z of the transistors in their circuitry, and with the specified output Z of the load (the antenna). Bottom line -- optimum load Z of a power amp is the impedance at which the amplifier, including its output filter circuitry, is happy. And the value of Z load is unlikely to be equal to the value of Z out. 73, Jim Brown K9YC _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
 Current Thread [Amps] Transceiver Output Impedance, Robert Carroll Re: [Amps] Transceiver Output Impedance, Peter Voelpel Re: [Amps] Transceiver Output Impedance, Saandy Eban Re: [Amps] Transceiver Output Impedance, Roger (K8RI) Re: [Amps] Transceiver Output Impedance, peter . chadwick Re: [Amps] Transceiver Output Impedance, David Cutter Re: [Amps] Transceiver Output Impedance, jeremy-ca Re: [Amps] Transceiver Output Impedance, Roger (K8RI) Re: [Amps] Transceiver Output Impedance, Carl Clawson Re: [Amps] Transceiver Output Impedance, Manfred Mornhinweg Re: [Amps] Transceiver Output Impedance, Jim Brown <= Re: [Amps] Transceiver Output Impedance, Peter Voelpel Re: [Amps] Transceiver Output Impedance, Manfred Mornhinweg