I agree also that the second antenna is for diversity but none of the
manufactures can answer why it is needed if spread spectrum is suppose to be
so innately fade resistant, even though the spread spectrum Wifi is using
now with CCK isn't really truly random anymore.

Russ N7QR
russm at ieee dot org

"Arthur" wrote in message
news
On Thu, 7 Oct 2004 12:00:52 +0100, Daniel Kelly (AKA Jack)
wrote:

I'm not a radio engineer so I'm not too sure what's going on. If I was
forced to make an educated guess then I'd say the problem was caused by
interference caused by reflected, out-of-phase signals. For example,
it's
conceivable that the receiver could be picking up two 'copies' of the
transmission from the TX - one 'copy' is the direct signal, the other
'copy'
is a signal that has bounced off some surface - these two 'copies' would
cancel eachother out when they're 180 degrees out of phase.

Yout assumption is absolutely correct


So... this brings me to the question I posed in the subject line: why do
WiFi basestations use two antennas? For example, my 3Com basestation
has
two little whip antennas sticking out the back. Are these two antennas
used
to combat the problem that I am experiencing? If so, how can I
implement
two antennas on my system?

It's a technique called 'space diversity' that is also used in many radio
systems such as radio microphones and cellular radio. Two separate
receive aerials are used, on the principle that they are unlikely to both
be in a null at the same instant. There are various techniques to
implement this which range from simply coupling the two antennas together
to having entirely separate receivers and just selecting the best signal.
In your case it will complicate things considerably I'm afraid.

-Arthur