Is a ham transmitter conjugate matched to its load?

Following on from KL7AJ on the Conjugate Match Theorem, KL7AJ on the Conjugate Match Theorem – analytical solution asked the question Is a ham transmitter conjugate matched to its load?

The answer speaks to the relevance of Walt Maxwell’s Conjugate Mirror proposition to ham stations.

If an antenna system is carefully adjusted (eg using an ATU) so that the transmitter sees a load with extremely low VSWR(50), the load is almost exactly 50+j0Ω.

It is conjugate matched to the source is the source is well represented by a Thevenin source with equivalent source impedance equal to 50+j0Ω.

Although ham transmitters are commonly designed and specified to deliver output power to a nominal 50Ω load, that does not necessarily mean that they are well represented by a Thevenin source with equivalent source impedance equal to 50+j0Ω. Indeed it would be most unusual for a HF transmitter to do so, but may be the case for microwave transmitters that use a suitably terminated circulator or isolator at their output. (Hams have a tendency to appropriate well known terms to different meanings, and isolator above does not mean a common mode choke as often meant by hams.)

It is important to understand that source impedance and load impedance are not referring to the same thing, they are two distinct entities, and ham transmitters are typically specified to suit a nominal load impedance, but most unlikely to specify the source impedance.

So, even if you have an antenna system with extremely low loss presently an extremely low VSWR, it is unlikely Walt Maxwell’s Conjugate Mirror utopia applies because of source mismatch.

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