Doesn't reciprocity assume similar antennas and similar
power levels?

Not both at once, I think.

The explanation I've seen of it is that if you have two radios having
identical transmitter power levels, then each radio's receiver will
"see" the same input voltage from its peer's signal even if the two
stations have wildly different antenna types (pattern, gain, takeoff
angle, polarization, etc.).

A change in one stations antenna which (e.g.) increases its gain in
the direction of the other, will increase both stations'
receiver-input voltage levels by the same amount... the changed
station "hears" the other station better, and also "speaks" better to
the other station by the same amount.

Naturally, the two stations may report different signal qualities
during the contact, depending on the sensitivities of their receivers,
on the local noise-floor level, on the presence of nearby in-band RFI
which desenses the receiver, on the meter calibration, on the
operator's hearing, on QSB which comes and goes at about the same rate
as the conversation changes directions, and so forth.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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