Hi Steve Thomas,
> Think about the receive signal. When it hits a mismatch, some portion
will
> be reflected back to the antenna, to be re-radiated and forever lost.
Not really. What really happens with a tuner in line is the system is
conjugately matched for the receive signal. Efficiency is no different on
receive as it is on transmit.
A rule of conjugate matching is this:
If the conjugately matched system is opened at any point and we look at
impedances both ways, the impedances at that point (looking both ways) will
always be the complex conjugates of each other.
So if, beyond the 20:1 mismatch, we add a tuner----- the antenna (now
receiving) will be driving a load that is equal to it's complex conjugate.
It will "see" the receive system as a perfect termination, the only loss
will be transmission line and matching system losses Eric outlined. System
loss will only increase by the increased loss in the feedline caused by the
higher currents and voltages that appear in the line due to its
mistermination. Mismatch loss does NOT come into play since the tuner
corrects the system with mismatch gain to restore match efficiency.
The only loss on receive will be EXACTLY the same loss as experienced
transmitting. As a matter of fact that is how I, and other engineers and
Physicists, measure some transmitting antenna systems. It is often done by
receiving, because the system always has exactly the same loss either way.
Kraus details this in his textbooks, as do others.
Eric was correct, and his data applies to receivers as well as
transmitters.
73 Tom
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