"Ron" wrote
Assume an incoming rf signal has exactly the same strength in all 3
dimensions i.e., completely omnidirectional. Question: would an antenna
having gain capture any more signal power than a completely
omnidirectional antenna with no gain?
__________

Whatever the net field that arrives from the transmit antenna (whether or
not the transmit antenna is omnidirectional), a receiving antenna having
gain in the direction toward the transmit antenna will perform better than
if it is omnidirectional.

Part of the improvement is due to its added gain, and part due to
interference rejection from co- and adjacent-channel signals arriving from
directions where the receiving antenna has less gain than an omni antenna.

RF