클럽에 질문을 올려 보니..
당사자인 테일러가 답변을 잘 해 주었습니다.
회로 해석하느라고 참 긴 시간 매달리고 있습니다.
찰거머리처럼요..
파워게인과 전압게인을 구별 못했으니 답변받고 어이가 없군요..

The Tayloe mixer does not have gain.  The input impedence is nominally
the 50 ohm impedence of the antenna, and the detector basically splits
the input RF into four different detector cap "buckets".  Thus, one 50
ohm RF input of 1v pk-pk will give four 200 ohm audio outputs of 1v
pk-pk.  There is neither a voltage or a power gain created here.
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I think it's important to distinguish between actual power gain, and just
voltage gain. Usually when we speak of a gain stage, it has power gain. To
get power gain requires an active device e.g. transistor, to control the
addition of more energy to the signal from the power supply.

Voltage gain can be obtained readily using passive devices e.g. a
transformer, but there is an associated impedance transformation which
ensures that there is no real power gain.

Similarly a polyphase network can be designed to have flat amplitude
response ( http://www.hanssummers.com/radio/polyphase/index.htm ), or even
to show a voltage gain. Just a bunch of resistors and capacitors. But
nothing is violated - there is no power gain - because the output impedance
of the network is much higher than the input impedance.