Build a Wi-Fi antenna using household materials

malcolmlewis · December 27, 2009, 3:56pm

Hi All
Thought this may be of interest…
http://www.h-online.com/features/Build-a-Wi-Fi-radio-relay-using-household-materials-747382.html

–
Cheers Malcolm °¿° (Linux Counter #276890)
SUSE Linux Enterprise Desktop 11 (x86_64) Kernel 2.6.27.39-0.3-default
up 12:26, 2 users, load average: 0.15, 0.11, 0.13
GPU GeForce 8600 GTS Silent - CUDA Driver Version: 190.18

smpoole7 · December 27, 2009, 4:37pm

A few points are in order. You can’t cheat physics; so-called gain in an antenna is achieved by limiting the signal in certain directions and increasing it in others. This is something we’ve been doing in radio for many, many decades – there are hundreds of AM directional radio stations all over the place.

With a simple whip antenna, “gain” is accomplished by flattening out the signal pattern: instead of wasting signal toward the ground and straight up into the sky, you focus it into a flat “pancake.” We do this in FM: my transmitters put out approximately 28,000 watts, but our antennas have enough gain to increase the effective power to 100,000 watts by focusing all of the power in flat, circular disk toward the horizon in all directions.

It’s real gain, too. If you have a meter that measures transmitter power, it will indicate the same as if I had a totally omnidirectional antenna with 100,000 watts of input.

A true directional antenna, such as the article’s can or a dish antenna, is even more restrictive. All of the signal is focused in one direction. You indeed get a lot of gain in one direction, but but at the expense of little or no signal in most other directions. Therefore, I’d dispute the author’s contention that it might help in the average home. If all you want to do is increase signal to one room, for example, it’s fine; but a directional antenna will NOT increase coverage throughout the home. That part of the article is misleading.

(If the antenna is highly directional, you could literally walk around the house with a laptop and watch the signal strength peg and then drop to nothing, all within a few steps.)

As the article notes, you can use this for wardriving or “borrowing” (stealing, really, if you don’t have permission) signal from someone else, but there’s a downside: anyone who happens to wardrive through YOUR directional beam will also be able to steal signal from YOU.

Ah, one other nitpick: the type “N” connector really isn’t the best for frequencies above 2 Gigahertz; there are others (such as TNC) that are preferred for low power, high-frequency work.

Finally, if you’re not very careful, if your antenna is constructed improperly, you’ll burn out the transmitter in the wireless access point.

malcolmlewis · December 27, 2009, 5:05pm

smpoole7:

A few points are in order. You can’t cheat physics; so-called gain in an
antenna is achieved by limiting the signal in certain directions and
increasing it in others. This is something we’ve been doing in radio for
many, many decades – there are hundreds of AM directional radio
stations all over the place.

With a simple whip antenna, “gain” is accomplished by flattening out
the signal pattern: instead of wasting signal toward the ground and
straight up into the sky, you focus it into a flat “pancake.” We do this
in FM: my transmitters put out approximately 28,000 watts, but our
antennas have enough gain to increase the effective power to 100,000
watts by focusing all of the power in flat, circular disk toward the
horizon in all directions.

It’s real gain, too. If you have a meter that measures transmitter
power, it will indicate the same as if I had a totally omnidirectional
antenna with 100,000 watts of input.

A true directional antenna, such as the article’s can or a dish
antenna, is even more restrictive. All of the signal is focused in one
direction. You indeed get a lot of gain in one direction, but but at the
expense of little or no signal in most other directions. Therefore, I’d
dispute the author’s contention that it might help in the average home.
If all you want to do is increase signal to one room, for example, it’s
fine; but a directional antenna will NOT increase coverage throughout
the home. That part of the article is misleading.

(If the antenna is highly directional, you could literally walk around
the house with a laptop and watch the signal strength peg and then drop
to nothing, all within a few steps.)

As the article notes, you can use this for wardriving or “borrowing”
(stealing, really, if you don’t have permission) signal from someone
else, but there’s a downside: anyone who happens to wardrive through
YOUR directional beam will also be able to steal signal from YOU.

Ah, one other nitpick: the type “N” connector really isn’t the best for
frequencies above 2 Gigahertz; there are others (such as TNC) that are
preferred for low power, high-frequency work.

Finally, if you’re not very careful, if your antenna is constructed
improperly, you’ll burn out the transmitter in the wireless access
point.

Hi
There you go all great points. So do you have suggestions for a
cheap directional antenna? Or better to spend some money on a proper
one? What I want to do is just point the signal from one wall towards
the back of the house and property. I get a good signal from the twin
antennas on the wrt54g, but wanted to reduce the noise from the others
around here…

–
Cheers Malcolm °¿° (Linux Counter #276890)
SUSE Linux Enterprise Desktop 11 (x86_64) Kernel 2.6.27.39-0.3-default
up 13:28, 2 users, load average: 0.00, 0.03, 0.05
GPU GeForce 8600 GTS Silent - CUDA Driver Version: 190.18

smpoole7 · December 27, 2009, 5:40pm

You could build one that will do that. I didn’t mean to pontificate, I just get tired of articles that act as though directional antennas are a Be-All, Cure-All for any wireless ills.

Build it and try it. Just be careful how you aim it – if you point it toward a neighbor’s house, they could get enough signal to steal from you. That matters because of the insane way that Hollywood and the RIAA want to hold YOU responsible if someone else happens to download copyrighted material on your connection, even without your knowledge.

That’s why I won’t even use wireless at home. I just run a 50’ CAT 5 when I bring the laptop home from work.

stakanov · December 29, 2009, 9:52pm

If it is a question of money:
Here is a link to a 0 Euro antenna (Yagi).
It does not cure everything (you will continue to go to the doctor with appendicitis). But it is fun building it and you can have a try. All you need is waste.
The article is in German. An automatic translator should do the trick.
If not, let me know I will see if I am still not too brain dead for a courtesy translation.
Cheers.

malcolmlewis · December 29, 2009, 10:03pm

Hi
Thanks for that Not an issue for money, was just wanting to play and
have some fun experimenting

I have an AP I can use (WET54G) as well if push comes to shove I could
just plug that in via cable (just need to get a POE unit).

–
Cheers Malcolm °¿° (Linux Counter #276890)
SUSE Linux Enterprise Desktop 11 (x86_64) Kernel 2.6.27.39-0.3-default
up 2 days 18:29, 3 users, load average: 0.19, 0.18, 0.20
GPU GeForce 8600 GTS Silent - CUDA Driver Version: 190.18

stakanov · December 30, 2009, 12:10am

I really appreciate this. Sometimes you get nice results. My brother captured the signal of AFN in Germany when we were kids, I think he was about 12. He did build a “cob-web” antenna against the wall. Well, helped to learn English and to be curious, no doubt. lol!

Enjoy your experiment and let me know next year (that I wish you to be a successful one BTW) how it did work out. Cheers.