Linux

wifi antenna

9 posts in this topic

Here are some pics of my recently completed wifi antenna!

Photo13.jpg

Photo14.jpg

Photo15.jpg

Photo17.jpg

Ok. Even though it looks like it is pointed into the ground, that feed is off axis, so that is actually pointing out 0º on the horizontal.

That base IS kind of flimsy, but it is realy impromptu, because I planed to mount those casters on the bottom of a box which I have already drilled to mount the antenna on top. I decided to say "screw the box" and just use this with a laptop instead, because we are going to try to get on top of a tall builidng with this, where there will be no electrical outlets.

Yes, that is a biquad feeding the parabolic. I don't know what the gain is, that is part of what I am going to test.

Look forward to a video starring this piece of equipment.

post-4287-1173235769_thumb.jpg

Edited by Linux
0

Share this post


Link to post
Share on other sites

Wow, very nice! Especially the biquad feed! I'll be interested to see how it performs; aren't waveguides ("cantennas") usually used to feed them?

The closest thing I've done to this is constructing a waveguide out of 3 1/2 inch steel conduit (the nice part about that being that you can pick the length).

What are the conditions you plan to test it under?

0

Share this post


Link to post
Share on other sites
Wow, very nice! Especially the biquad feed! I'll be interested to see how it performs; aren't waveguides ("cantennas") usually used to feed them?

The closest thing I've done to this is constructing a waveguide out of 3 1/2 inch steel conduit (the nice part about that being that you can pick the length).

What are the conditions you plan to test it under?

Thanks. Yup, many people use cantennas to feed these, but from what I have read, using a biquad will give you higher gain. Maybe about 30db?

We are going to take this to the top of Commonwealth Stadium here at UK, and point to a friend with an access point set up a known distance away (we will use a bicycle odometer to measure ground distace , and measure or lookup height of stadium and use good old pythagorean theorem. Or use GPS if someone has it.) That way, we can be sure there are no obstructions, etc. It really is the best way to get a clear line of sight around here, due to trees and hills! If we can use the GNU wireless utilites to measure signal strength, and given an known power output on this transmitter, and the gain of the antenna on the other end, we should be able to measure the gain of this dish (this is of the top of my head, I will look this up for the formulas).

Also plan to do all the standard wifi tricks. WPA/WEP, deauth DoS (on our own AP, of course) passive scans - we should get a good 200 APs - and maybe point this at a passive repeater.

Edited by Linux
0

Share this post


Link to post
Share on other sites

I mounted it on the 45º pipe, and set it to 45º (there is an adjustment slot on the upper dish mount, you can't see it in the photo). This is what the guys on the engaget article did, and it seems they did a pretty thorough test.

I haven't had a chance to really have it out in the field yet.

Edited by Linux
0

Share this post


Link to post
Share on other sites

Not to thread jack but how big of an antenna can you legally have (dbi wise) I read part 15 of the FCC laws but they where so vague and only talked about FM.

0

Share this post


Link to post
Share on other sites
Not to thread jack but how big of an antenna can you legally have (dbi wise)

If nobody notices is it really illegal? <_<

Edited by Drake Anubis
0

Share this post


Link to post
Share on other sites
Not to thread jack but how big of an antenna can you legally have (dbi wise) I read part 15 of the FCC laws but they where so vague and only talked about FM.

As big as you want.

The FCC regulates RF input power into the antenna, per FCC Part 15.247.

For every 3 dB of gain your antenna has over 6 dBi, you must reduce your RF input power by +1 dBm. Maximum antenna RF input power is +30 dBm (1 watt).

High-gain antennas are encouraged for Part 15 use, as their narrow bandwidths help to reduce interference to others.

-1

Share this post


Link to post
Share on other sites
High-gain antennas are encouraged for Part 15 use, as their narrow bandwidths help to reduce interference to others.

They are often a better solution than 'more power' as it's really the noise floor on the reception end which limits how far you can transmit.

However greater gain requires more precise aiming and mounting.

I found this great online book (http://wndw.net/) which describes how to do a proper link budget:

http://wiki.wndw.net/moin/English/Chapter3...b1942976342a8d2

Cheers,

Munge.

Edited by mungewell
0

Share this post


Link to post
Share on other sites

I really like this hack, and have been planning for a while to do it. I do have a few questions, Linux. The Engadget article requires the RP-MMCX pigtails, however, I do not have access to a connector of this type. What pigtail did you use on it? Would this antenna hack work with a RP-SMA pigtail?

For all those wondering how Linux did this, there's an Engadget article, but since the pictures are all gone, the Internet archive has them here.

0

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now