Re: How to choose an antenna?

On Jan 7, 7:54 pm, rickyricardorockero <rickyricardorockero.32u...@no-
mx.wirelessforums.org> wrote:
> Hello, I'm trying to find a good antenna to extend the range of my
> wireless network. I don't know how to choose one. What im trying to
> figure out is the maximum distance that a particular antenna can radiate
> signals according to its transmitting power, antenna gain, and
> frequency. :huh:For example im looking at an antenna with a power input
> of 200mW and a 7dBi gain at 2.4GHz. That is all the information that the
> manufacture gives.:mad:
>
> ------------------------------------------------------------------------
> View this thread:http://www.wirelessforums.org/showth...lessforums.org

You want to map out your whole system from where you are to where you
want the signal to reach. Then you add in all the known elements and
see how much radio power and antenna gain you need. This is called a
"link calculation or power budget".

More explanation and calculators on this site:

http://www.zytrax.com/tech/wireless/intro.htm

Read up on things there, then go to their calculators and start
plugging in your numbers. You will soon see how much gain you need to
get a 20 db signal to noise (minimum). Decisions about whether to get
an omni or directional antenna and how narrow of beam will depend on
whether you are going point to point or point to multipoint. Sort of
like, do you need a laser pointer, a spotlight, a flood light or just
an open light bulb.

A big issue that is often missed when just buying antennas from stores
or even online is the attached cable, if there is one. I avoid
attached cables, unless VERY short, as they introduce loss. The specs
on the antenna never include what is lost in the often cheap, thin
cable.

One thing: At the linked site above, their rule of thumb on cable loss
is not right. Go here for accurate calcs on antenna cable loss:
http://www.timesmicrowave.com/cgi-bin/calculate.pl
Plug in 2400 under Mhz and choose between LMR 100,200 and 400 to check
common cable loss, for short medium and long runs.

Finally, there is another site that is recommended for orientation on
WIFI:

http://wireless.wikia.com/wiki/Wi-Fi

It covers a lot more ground than the other link, lots of good info is
there if you look for it.

Steve