1. No, access points cannot use one for transmit and one for receive. The reason is that both antennas connect to the same radio, and the radio itself can only transmit or listen, never both at once.
2. Diversity is receive diversity. Transmitting the same signal twice would just make multipath worse :)
A few other points that should hopefully make things a bit clearer:
- Only one antenna is active at a time. The radio uses one to transmit a signal, and it flips between the two antennas very quickly while receiving.
- Diversity works by comparing two similar signals and seeing which one is stronger. The real advantage gained from diversity is the physical separation of the antennas. Since they're located in two different spots, the signal will vary between these two spots, and the AP can pick which one of these spots has the better signal at any given time.
- Diversity antennas should never be deployed to create two separate coverage areas. The two antennas should be identical, be deployed identically, and be intended to create a single coverage area. They should be as close together as possible, and they should be some multiplier of the frequency's wavelength. Using rubber duck antennas on a Cisco AP takes care of all of these points, but you need to keep them all in mind if you ever use detached antennas.
I hope that helps!
Jeff
