# Re: 31 db gain antenna

• From: Jeff Liebermann <jeffl@xxxxxxxxxx>
• Date: Sat, 01 Nov 2008 10:17:45 -0700

On Fri, 31 Oct 2008 19:50:33 -0700 (PDT), jimmie68@xxxxxxxxx wrote:

While working on an airport S band radar I taped my WiFi detector to
the feedhorn and rotated the antenna. I was picking up signals from
all over the place, at least 100 different ones probably more that I
could not discern from the others. With the detector removed from the
feedhorn I could only get 4, I think they are all the WiFI for the
airport.Gain of the antenna is 31db with a cosecant squared vertical
radiation pattern. Its amazing what a really good antenna will do.

Jimmie

Doing the math.... well maybe not... my calculator battery just died.
Ok, the hard way... range doubles with every 6dB of gain.
gain = range increase over 0dBi gain
6dB = 2x
12dB = 4x
18dB = 8x
24dB = 16x
30dB = 32x
So, you've picked up perhaps 32 times the range or 32^2 = 1024 times
the coverage area with the rotating antenna. If you assume a uniform
density of access points, you should hear 1024 times as many. Nice.

The local airport (WVI/KWVI) has about 100 access point scattered
around the hangars, neighboring businesses, flight skools, and airport
offices. My guess is about 25% are wide open and set to the default