FightingBlue
@direcpc.com
| How good of a 2.4 GHz omni antenna can you get?
I've usually seen 12 dbi omnis listed as the highest gain you can get, but I wonder. I've also seen a couple of references to higher gain 2.4 omnis, 13 and 15 dbi. How high can you actually go? If you built it yourself, for instance, could you make a 20 dbi omni? 28 dbi? 30? And is it technical limitations, or regulatory concerns that limit the antenna gain? |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
2 edits | Re: How good of a 2.4 GHz omni antenna can you get
said by FightingBlue :
I've usually seen 12 dbi omnis listed as the highest gain you can get, but I wonder. I've also seen a couple of references to higher gain 2.4 omnis, 13 and 15 dbi. How high can you actually go?
There are physical limitations to how large an omni can be. There are also electrical limitations. If you find a 16 dBi vertically polarized omni you will have found something about six or seven feet tall which has a very narrow beamwidth.
said by FightingBlue :
If you built it yourself, for instance, could you make a 20 dbi omni? 28 dbi? 30? And is it technical limitations, or regulatory concerns that limit the antenna gain?
FightinBLue 
Please take what follows with a huge portion of salt, I just couldn't resist having fun with the idea. The numbers are close enough to be called "correct  ", I checked 'em myself.
If you built it yourself and you were very careful you could probably build a 21 dBi gain horizontally polarized slotted wave guide antanna. I have built one to a measured 13 dBi and it was about five feet long. A 21 dBi gain slotted wave guide antenna would have about 75 slots on each side, would be about 25 feet long and would have a beam width of about .8 degrees.
You could even build a 50' version that gave you 24 dBi of gain with a beam width of .4 degrees. Then you could dispense with the tower and simply tie it to a stake in the ground. The center of the antenna would be 25 feet off the ground. You would also reap the additional advantage that no trees in your area could grow taller than 25 feet as the radiation would trim the limbs automagically as they grew into the beam. I think 25' is a good height for trees anyway.
Me, I'm working on the 30 dBi version. It is going to be 200 feet tall and have 600 slots on each side! We are just strapping it to the side of our tower with 16 foot standoffs every 10 feet up the side of the tower. Got me a killer ten watt amp we are going to drive with a WAP-11 (I hear the third party Linksys firmware will let me get 250 mw out of that puppy!). Yeah! That's what I am talking about! Alleygator city! Ya better watch out 'cause DaDogs Tower is gonna be talkin'. I'm just worried that a .1 degree beamwidth at 100' won't hit the ground for about ten miles, but hey, the grass will smolder where it hits the ground!
Yeah! Scorched spectrum, that's my motto!
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Now where did I leave that 2 KW linear?! |
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John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
 ·CenturyLink
| said by DaDogs  :There are physical limitations to how large an omni can be.! In no case can the antenna exceed the limits of the boundries of the universe.
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A is A |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
| said by John Galt :said by DaDogs :There are physical limitations to how large an omni can be.! In no case can the antenna exceed the limits of the boundries of the universe. Damn FCC rules! Who needs them anyway?!
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Improve your wireless signal! |
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polk5
join:2001-12-29
New Orleans, LA | reply to FightingBlue
Re: How good of a 2.4 GHz omni antenna can you get?
I use the 15dbi omni's often for RV parks and other things that do not need height. Over 15dbi and it does not have many applications. Thats why you do not see them manufactured for the most part. |
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VariableARK
join:2003-03-17
USA | reply to FightingBlue
Re: How good of a 2.4 GHz omni antenna can you get
fcc rule? i think that may be a law of physics or something like that. lol |
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superdog
I Need A Drink
Premium,MVM
join:2001-07-13
Lebanon, PA
| reply to DaDogs
said by DaDogs :Yeah! That's what I am talking about! Alleygator city! Ya better watch out 'cause DaDogs Tower is gonna be talkin'.Yeah! Scorched spectrum, that's my motto! LMAO!!!:D. That was a fantastic way to use humor to answer a question!!, I LOVE IT!!:)
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»www.wavecrazy.net Join WISPA today! »www.wispa.org/ |
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anoclon
join:2004-10-12
Guatemala
| reply to DaDogs
If the bigger the Dbi on an omni, the taller it is, why I've seen a 15Dbi Hyperlink omni that is about 4 feet tall but thicker than a 15Dbi D-link omni that is about 6 feet tall?. According to "DaDogs'" humor and numbers they should be the same tall. Why then the difference in their sizes? |
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DaDogs
Semper Vigilantis
Premium
join:2004-02-28
Deltaville, VA
| said by anoclon :If the bigger the Dbi on an omni, the taller it is, why I've seen a 15Dbi Hyperlink omni that is about 4 feet tall but thicker than a 15Dbi D-link omni that is about 6 feet tall?. According to "DaDogs'" humor and numbers they should be the same tall. Why then the difference in their sizes? There are two basic kinds of omni antennas. Those with vertical polarization and those with horizontal polarization. I suppose one could also build one with circular polarization but I'd have to give that some thought and study.
Anyway, usually a vertically polarized omni is built up of a long piece of wire with loading coils every so far along the wire. The longer the wire and the more coils the higher the gain. Another type of vertically polarized omni antenna is build up using dipoles or folded dipoles driven in phase. That kind will be longer than the first kind.
The omni antennas that look sort of like a 2x4 and are shorter than the vertically polarized "whip" looking antennas, are horizontally polarized slotted wave guides. That kind is made by cutting slots in a wave guide which act like dipoles and radiate from the wave guide. That kind usually gets more gain-per-foot than the vertically polarized antennas because the slots are shorter than a real dipole.
Those things said, given any specific type of antenna, omni or otherwise, some dimension will almost always double in order to double the gain. If it is a Yagi, the length will double. If it is an omni the length will double. If it is a dish the area of the dish will double. This happens because of a thing called "aperture". You can think of it like the aperture in a single lense reflex camera (I know, I know, most of you have never seen one ... Gawd, I am gettin old). Anyway on a camera when you want more exposure (more power) you open the aperture either longer or larger. If you want to double the power you open the aperture twice as long, or twice as big for the same amount of time.
You can't open the antenna for twice as long (but there are some cool things you can do with the signal itself, like spread spectrum). You can make the antenna twice as big. Since 3 dB represents a doubling in power, every time you get another 3 dB you need to double something about the antenna.
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A free 12 dBi antenna? |
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kewlkeed
Grouch
Premium
join:2005-02-05
Knowlton, QC
| reply to FightingBlue
Re: How good of a 2.4 GHz omni antenna can you get?
LMMFAO!!!!!!
I'm just curious if something like this was done on one of thoes WIFI plus so called multi-polarized antennas...
Methinks that would just get ugly.
This just made my day. So who can I contract to build one of these puppies? I never liked trees in my way anyhow.
Good one indeed! And who says math is boring  |
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public
join:2002-01-19
Santa Clara, CA
·DSL EXTREME
| reply to DaDogs
Re: How good of a 2.4 GHz omni antenna can you get
said by DaDogs : Anyway, usually a vertically polarized omni is built up of a long piece of wire with loading coils every so far along the wire. The longer the wire and the more coils the higher the gain. Another type of vertically polarized omni antenna is build up using dipoles or folded dipoles driven in phase. That kind will be longer than the first kind. You can build a vertically polarized omni with alternating 1/2 wave sections of coax. The number needed for a given gain grows rather quickly beyond about 10dBi.
The slotted waveguide can also be turned into a 180 sector by making slots only on one side. |
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public
join:2002-01-19
Santa Clara, CA
·DSL EXTREME
| reply to kewlkeed
Re: How good of a 2.4 GHz omni antenna can you get?
said by kewlkeed :LMMFAO!!!!!! This just made my day. So who can I contract to build one of these puppies? I never liked trees in my way anyhow. Try DARPA. They had several PW class pulsed power projects. |
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