confusion about wlan antennas

antenna mounted

PC showed 6 AP's

and the rest were

na picked up 12

found was weak,

in antennas? What

G213 cable with

length for both

My theory is: It is all related to the meaning of "antenna gain". Why is it that one is said to have 6dB and the other 15dB? Think for a second... antennas does not have power plugs, so they don=B4t add power... how one can have more "energy" than the other? Here lies is the answer for your question. What an antenna with bigger gain does is concentrate the signal in a smaller area (or volume if you will, as it is 3D), so the area that is serviced get more signal (sacrificing other areas that will bet weaker signal). The same happens with reception, the bigger the gain, the smaller is the region it will do a good "listening". So an omni 15dB antenna only gets good signal from APs antennas that are on the same height as it. If the origin AP is slighter higher or lower (can be as little as few metters) it will get a weak signal. Your 15dB can hear far, but your neighbors APs (the first 6 ones) are not so well aligned with it, so the signal gets weaker.

showed 6 AP's

the rest were

antennas? What

cable with

length for both

I am not an RF guru, but a little reading around suggests to me that

a) you should definitely be using a 50 ohm coax like RG58 or your RG213 rather than standard 75 ohm TV drop cable, which has high frequency losses which are just way too high, and

b) those cable runs are long - you can get signal attenuation well over

1 dB/meter at 2.4GHz, even with RG58 (I don't know about RG213, but it's probably a little better).

I think the rule of thumb is to put the router as close to the antenna as possible, then run CAT5 from the router to where you need it.

Compare these two articles, for instance:

1. formatting link
   formatting link