Tall Wifi Antenna

EBFoxbat · 08-31-2004, 10:34 AM

I'm going to put a 48" Whip antenna on my truck for the CB radio. I don't know much about antenna physics, but I need an antenna for my wifi.

I know I cant use that because its tuned for CB radio range. Can I get anotehr tall antenna tuned fo wifi that is similar in length? I'd like to have one on each side. thanks.

VWMAN · 08-31-2004, 10:48 AM

Try this place

http://www.radiolabs.com/products/wi.../wireless.html

gizmomkr · 08-31-2004, 10:58 AM

Generally speaking , due to the waveleginth - (WiFi has a mutch shorter waveleginth than CB Frequencies) I think it would be rare to find a wIFi of similar leginth. Even the ones listed on that site are 2 ft max. Most CB whip antenna I see are closer to 6....

john1701 · 08-31-2004, 07:00 PM

here is some wifi antennas that might interest you,
I have the 8db omni 20 inch mounted on my car.

http://www.hyperlinktech.com/web/ant...0_out_omni.php

longwoodtrail · 08-31-2004, 07:05 PM

Is it not possible to create a 6ft antena for 2.4ghz range? What I am trying to ask is, is this outside the parameters for WiFi, or do manufacturers simply not make them?

ppgt94 · 08-31-2004, 08:29 PM

I got a really nice 9dB wifi antenna from ebay. I think they might be all gone now. The member was Mhzkid or something like that.

S80 · 09-01-2004, 02:13 AM

Ok. Let's see if I remember this correctly!

The length of an "full length antenna" is determined by the wavelength of the frequency that you will use it for.

To calculate the wavelength you do something like this:

Speed Of Light = 299,792,458 meters per second
Speed Of Light/frequency = wavelength
299,792,458/2.4GHz = 0.125 meters = 4.9 inch

So the optimal length for a 2.4GHz antenna should be 4.9 inches or 12.5cm.
You can also use half length and quarter length antennas. (3.95" or 1.97")

It was a long while since I did this kind of calculations but I think that they are correct!

/Niklas

erazor · 09-01-2004, 03:18 AM

Quote:

So the optimal length for a 2.4GHz antenna should be 4.9 inches or 12.5cm.

but as far as i know you could also make tha antena x * 12,5cm so you can have 25, 50, 100 but an larger antenna means lower signal as said optimal is 12.5

S80 · 09-01-2004, 03:39 AM

Quote: Originally Posted by erazor

but as far as i know you could also make tha antena x * 12,5cm so you can have 25, 50, 100 but an larger antenna means lower signal as said optimal is 12.5

Yes, thats right!

kiltjim · 09-01-2004, 10:32 AM

Quote: Originally Posted by longwoodtrail

Is it not possible to create a 6ft antena for 2.4ghz range? What I am trying to ask is, is this outside the parameters for WiFi, or do manufacturers simply not make them?

If you look around, you will find extensive equations on building one from coaxial cable. Different cable means different velocity factors.

In thoery, you could build an antenna that is 6 foot in length, but you would need an extremely low velocity factor, or an extremely large gain.

Problems with both: A low velocity factor is going to be pretty hard to find. You would probably end up using something different than coax cable to achieve this.

An extremely high gain antenna is going to limit your effective range. Look
around for better explanations of this, but imagine a balloon. An unsqueezed balloon would be your low gain antenna (~3 dB). So so range all around. Now, squeeze it. The sides are much further from the center, but the top and bottom are now much closer. A huge gain antenna is going to have a horrible range outside of directly horizontal to the car.

Also, the difference in appearance between the CB whip and a rigid WiFi antenna is going to be significant. You are not going to find a whip, it just does not exist.

Change · 09-01-2004, 11:46 AM

Quarter-wave gives quite good performance for most applications. A half-wave antenna has the bonus of not requiring a groundplane (most antennas need at least a quarter wavelength of groundplane around them, that is a disc of grounded conductive material) and will give you higher gain.

Gain with antennas means it will give more "oomph" to the transmitted signal and be able to pick up quieter signals, but it decreases the radiation lobe patterns. A quarter-wave antenna will radiate and receive signals just about straight out from the groundplane to about 45 degrees up. A half-wave antenna narrows that lobe, maybe to about 20 degrees up or so. Higher gain antennas narrow the lobes even more. Directional antennas have fantastic gain characteristics, but only in one direction.

Check out these URLs for more (And better) explanations of antenna basics:
http://www.electronics-tutorials.com...nna-basics.htm
http://w1.859.telia.com/~u85920178/antennas/anten.htm

kandyman676 · 03-07-2005, 10:43 PM

Quote: Originally Posted by john1701

here is some wifi antennas that might interest you,
I have the 8db omni 20 inch mounted on my car.

http://www.hyperlinktech.com/web/ant...0_out_omni.php

and you have that mounted on your car how? LOL

dave2 · 03-09-2005, 04:33 AM

I know what you want to do. I get it. Anyways, do some creative engineering. Get your best wifi omni antenna. Get a cheapo CB antenna from radio shack, a nice big one, or whatever matches your other antenna. Build something that will bracket that antenna to the top of the other one, or run it right in back of it, truck side.

Problem is, you probably want to mount it low on the truck, and the truck will shield it from the other side. Just try to make the wifi antenna look like the cb antenna.

You will gain nothing by making a wifi antenna 6 ft long. You could also get a hollow fiberglass pole, to match the other side, run your coax up through it to a proper antenna at the end. Just get one of those small wifi antennas, and put it inside the tube, hot glue it in place or something.

Good luck!

nevtxjustin · 10-16-2005, 04:55 PM

WHOOOAAA Trigger...Lets to back to Antenna Basics 101.

*** First the math for the middle of WiFi band (2412-2462 MHz):
Wavelength is:
300,000,000 meters/sec. divided by 2,437,000,000 cycles/sec. = .123 meters
or simply 300/2400 MHz = .123 meters
For a quarter-wave radiator:
.123/4 = .0308 meters or 3.08 cm
Converting to inches:
3.08 cm = 1.20 or 1-3/16"

*** Second a quarter-wave dipole plane and ground plane antenna:
A dipole is to opposed radiators, like a "T". It has UNITY GAIN or zero gain.
A ground plane replaces one of the radiators where the ground plane is at least 2 wavelengths in diameter.
Therefore a 9" pie pan with a radiator poking up through it works fine as a UNITY GAIN antenna compared to a dipole.

*** Third - What is Unity gain?
Depends on the standard you are comparing to.
Commercial communication antenna manufactures have always used "gain over a dipole" comparison in the past.
WiFi antenna manufactures use "gain over an isotropic source" comparison.
I'll skip the explanation and just give figures for comparison where dBi and dBd stand for decibels of isotropic and decibels over dipole.
0 dBi = -2.15 dBd 2.15 dBi = 0 dBd (a dipole or ground plane)
3 dBi = .85 dBd 5.15 dBi = 3 dBd is 2x the gain over a ground plane
6 dBi = 3.85 dBd 8.15 dBi = 6 dBd is 4x
9 dBi = 6.85 dBd 11.15 dBi = 9 dBd is 8x
10 dBi = 6.85 dBd 14.15 dBi = 10 dBd is 10x
So if you want to compare real life antennas, build yourself a simple ground plane for your standard.

*** Fourth - What is a "long antenna"?
You can "stack" the radiating elements for more gain. Each radiating element must be spaced 1/4 wavelength apart.
If length is not a problem, you can use an out of phase element for the spacer; but it is a problem as in mobile antennas, then you replace the spaced with a physically short (but still an electrical quarter wavelength long) coil of wire.
Each additional radiating element ARRAY gives an additional 3 dB for gain (a doubling).
There is such a thing as a "long wire antenna". Its called a Zepp Antenna (Just Goggle for the damn explanation)

*** Fifth - What is an ARRAY?
Its the correct multiples of quarter wavelength radiators

Tilted on the side, a ground plane looks like this:
---|

A two element co-linear antenna (3 dB gain):
---***---|

A four element co-linear antenna (6 dB gain):
---***---***---***---|

An eight element co-linear antenna (9 dB gain):
---***---***---***---***---***---***---***---|

Now...on to my responses...............

EBFoxbat is looking for a cosmetically matching antenna mast.
"Can I get anotehr tall antenna tuned fo wifi that is similar in length? I'd like to have one on each side. thanks."

gizmomkr answered with:
"Even the ones listed on that site are 2 ft max. Most CB whip antenna I see are closer to 6."
*** CB (27 MHz 0r 11 meter antennas can be just about any length. From a 9' (108" or 96" with 6" spring) quarter-wave ground plane to an inductively loaded whip (usually wire wound around a fiberglass rod) usually 4' long.

longwoodtrail pondered:
"Is it not possible to create a 6ft antena for 2.4ghz range? What I am trying to ask is, is this outside the parameters for WiFi, or do manufacturers simply not make them?"
*** No. It would be 60 element co-linear antenna. The losses from all the joints would defeat an gain.

S80 calculated:
"So the optimal length for a 2.4GHz antenna should be 4.9 inches or 12.5cm."
*** If you are thinking of a simple quarter wave antenna, no. It would be 3.08 cm.

erazor offered:
but as far as i know you could also make tha antena x * 12,5cm so you can have 25, 50, 100 but an larger antenna means lower signal as said optimal is 12.5
*** I'm not clear what you're saying. See my response to longwoodtrail.

kiltjim theorized::
"In thoery, you could build an antenna that is 6 foot in length, but you would need an extremely low velocity factor, or an extremely large gain."
*** See my response to longwoodtrail. Velocity factor has NOTHING to do with it, you're thinking of the LOSS FACTOR. Velocity factor is used in another part of the calculations altogether.

and added:
"Also, the difference in appearance between the CB whip and a rigid WiFi antenna is going to be significant. You are not going to find a whip, it just does not exist."
*** Take the 6' CB antenna and drop a piece of 1/2" PVC over it. Stick a USB WiFi dongle in another 1/2" piece of PVC and mount it on a spring.

"I knew you could do it..." <-- Mister Rogers, circa 1980

fire · 11-03-2005, 06:44 AM

nevtxjustin lectured:
lots of information

damn.. awsome post.. i learnt so much..

.. good work