Re: dipole vs. omni-d

seesoe <seesoe.2z4oma@no-mx.wirelessforums.org> hath wroth:

>what would be best for a robot, im feeding the robot from a 8dbi omni
>directional

The robot eats antennas? I would feed it something less expensive.

Are you using 2.4Ghz Wi-Fi or something else? Perhaps it would be
useful if you disclose what hardware and software you have to work
with and in what environment you plan to use the robot.

>and now i need a antenna for the robot, but im not sure if i should use
>a 5 / 8 dipole with something like ' this' (http://tinyurl.com/2pryuk)
>or a car mounted omni-directional like 'this'
>(http://tinyurl.com/36vux3)
>
>what do you guys think?:confused:

I've helped with a few 2.4GHz wireless robots. It's amazing how much
RFI (radio freq interfernce) a high power motor controller can
generate. 2.4Ghz works just fine as long as there is no
interference[1] and your traffic is minimal. If you're running 30fps
video over Wi-Fi, give up now.

Since you didn't specify a distance requirement, I can't really offer
any specific suggestions. Up to about 50 ft, with no obstructions,
almost any omni antenna will work. If you plan on going farther,
you'll need to make some changes. Since you don't know the robots
orientation, I suggest you move the omni to the robot. Yeah, I know
it's a big long antenna. At the control point, I suggest anything
between a 12dBi panel antenna, which should have about a 45 degree
beamwidth. Any more gain will require some form of tracking. I've
done this for model airplanes using 2.4GHz Spektrum RC hardware:
<http://www.spektrumrc.com>

You might find this interesting for your bot:
"World Smallest Longest Range 2.4 Ghz Radio Remote
Control Wireless RC Camera":
<http://www.nitroplanes.com/wosmlora24gh.html> $70.
If you pick your channels carefully, it sorta coexists with Spektrum
and Wi-Fi radios.

[1] We staged a private autonomous maze run at the local university
and had to disarm the wireless access point in the room. If we pulled
the plug, alarms would go off all over place. So, I just unscrewed
both antennas on 3 access points.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558