Even considering an ideal S-meter ... If the
wanted signal is not strong enough to overwhelm al other contributions,
doubling
the transmit power will not turn into a 3-db S-meter reading increase.

It would have to. Any additional power to the general spectrum is
going to raise the power in the spectrum - even if you cannot
distinguish it. That is, afterall, how the spectrum gets to become so
noisy. If you are tuned to the radiator that has gone through a power
boost, then your S-Meter should indicate it.

73's
Richard Clark, KB7QHC

Yes, but not quite 3dB when transmit power is doubled. A 3-dB increase would
only occur if the "wanted" signal would be alone in the receiver bandwidth (viz
no background noise, no interfering signal).

73

Tony I0JX