nevtxjustin

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