Post Your Homebrew Antennas Here

lincomatic · 05-29-2002

ok, since measurements of the mobile mark antenna don't seem too be forthcoming, i decided to take the bull by the horns and design an omni from scratch. come on everyone, if you have a homebrew antenna post it here. let's use this thread for antenna brainstorming.

first, let me make it clear that i really don't know a damn about RF design. spent several hours at the library, borders books, and perusing the web. then i downloaded the EZNEC demo from
http://www.eznec.com
and started messing with it.

i still don't have a good grasp of how to model a real ground plane, but i was able to get some plots and start tweaking things. i started w/ a quarter wave whip. In the US, channel 6 is the middle channel at 2.437GHz. this makes a quarter wave about 30.6mm.
so i started with this and just experimented w/ various lengths to change the pattern and SWR and ended up with 89mm. EZNEC shows SWR of 1.2-1.6 over the WiFi band and gain of 4.35dB max assuming a perfect ground (which we don't have).

so here is my prototype. it's just a piece of 2mm dia. coat hanger cut to 87mm and soldered into an N-female panel jack for 89mm length from the tip to the base of the middle pin on the jack. just for the hell of it i soldered on the ground plane, which is the lid of a 3.25" dia. tin can. the tape is just to keep me from shredding my fingers on the sharp edges.

how well does it work? i was amazed. walking outside with ministumbler, i can find my AP 120ft farther away than with the ORiNOCO built in antenna. inside the house, i went the the place w/ the worst reception and the signal & SNR went up by over 10dB vs the built in antenna. i haven't even begun to tweak the thing yet. not bad for a $4 antenna (the cost of the N jack).

i've created a web page for my homebrew experiments at
http://www.geocities.com/lincomatic/homebrewant.html

blackwave · 05-29-2002

Ah, but can you wear it like this?

(See attached)

lincomatic · 05-29-2002

i guess could also feed the tip thru the top of a baseball hat for war walking and look like a total dork, too

just stumbled w/ it for the first time on the way to work and it picked up a few AP's i didn't know existed

acidrayne · 05-29-2002

Quote:

Originally posted by lincomatic
i guess could also feed the tip thru the top of a baseball hat for war walking and look like a total dork, too

just stumbled w/ it for the first time on the way to work and it picked up a few AP's i didn't know existed

I think attaching a propellar to it and wearing it as a beanie cap would be nice!!

Didnt someone have a pic similar to this posted at one point?

blackwave · 05-29-2002

Quote:

Originally posted by acidrayne

I think attaching a propellar to it and wearing it as a beanie cap would be nice!!

Didnt someone have a pic similar to this posted at one point?

Click here

http://forums.netstumbler.com/showth...g&pagenumber=2

sparafina · 05-29-2002

I built a similar antenna, but I mounted it on the bottom of a yogurt cup, cut a slit for the pigtail, glued a speaker magnet to the inside of the lid and snapped it back on, voila - instant magnetic mount.

lincomatic · 05-29-2002

sparafina: post a photo! and tell us what length you chose and why.

acid: haha, that beanie idea isn't a bad idea for hiding the antenna but the dorkiness of it would attract too much attention

acidrayne · 05-29-2002

Quote:

Originally posted by blackwave

Click here

http://forums.netstumbler.com/showth...g&pagenumber=2

Thanks for the link BW ... That is the one I was thinking of.

Linco ... You know the chicks would dig it.

blackwave · 05-29-2002

Quote:

Originally posted by acidrayne

Linco ... You know the chicks would dig it.

Oh I can see all those oiled up bikini silicon filled stumbler groupies lining up now... oh yea...

outcast_one · 05-29-2002

I was hoping otaku42 would post the pics fairly quickly, but there seems to be some delay. I will post two of them here, the rest will appear on his site when he has it finished. These pics are low res due to the file size limit of the forum.

outcast_one · 05-29-2002

here it is

gcrocker · 05-29-2002

Not that appropriate for stumbling (it's 20" high and PVC), but I may mount it on my crappy van for just that purpose:

http://www.guerrilla.net/reference/a...r_omni_lowpwr/

First one I built took 3-4 hours, and I think I can do them in an hour now.

-glenn

sparafina · 05-29-2002

Quote:

Originally posted by lincomatic
sparafina: post a photo! and tell us what length you chose and why.

I came up with 73 mm based on a 5/8 wave whip. Uusing the antenna elmer at http://www.qsl.net/w4sat/five8th.htm, I got 178.308/2437. No groundplane, I figure the car would be sufficient

Sorry no pics on the 5/8 whip, left the camera at the in-laws. I'll post it later when I retrieve it from them over the weekend. A pic of the cantenna and rig are here:

http://forums.netstumbler.com//showt...5&pagenumber=2

Used a Bush's bean can; although I found chili and spaghetti-os cans that were tall enough, they looked too disgusting to deal with. Used the beans in a lamb cassole, yum. Perhaps that should be a thread: Cantenna Recipes

lullabud · 05-30-2002

Quote:

Originally posted by gcrocker
Not that appropriate for stumbling (it's 20" high and PVC), but I may mount it on my crappy van for just that purpose:

http://www.guerrilla.net/reference/a...r_omni_lowpwr/

First one I built took 3-4 hours, and I think I can do them in an hour now.

-glenn

dude, post photos and design notes!

also, for those who want yet another tutorial on the pringles can my friend dr. nazo built a nice one and took photos of the process.

sykojester · 05-30-2002

just looked @ the pics (too busy to read everything else right now), but I know I wouldnt dare go out w/ it the way it looked. I thought it was nice and all, but man, that looked like a pipe bomb. LOL. esp all black.

05-29-2002	#3 (permalink)
lincomatic Squaaawk! WiFi! WiFi! Join Date: Apr 2002 Location: Tinsel Town Posts: 1,682	i guess could also feed the tip thru the top of a baseball hat for war walking and look like a total dork, too just stumbled w/ it for the first time on the way to work and it picked up a few AP's i didn't know existed __________________ ~lincomatic

05-29-2002	#7 (permalink)
lincomatic Squaaawk! WiFi! WiFi! Join Date: Apr 2002 Location: Tinsel Town Posts: 1,682	sparafina: post a photo! and tell us what length you chose and why. acid: haha, that beanie idea isn't a bad idea for hiding the antenna but the dorkiness of it would attract too much attention __________________ ~lincomatic

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

05-29-2002	#6 (permalink)
sparafina Registered Member Join Date: May 2002 Location: TX,MD,NY Posts: 1,430	I built a similar antenna, but I mounted it on the bottom of a yogurt cup, cut a slit for the pigtail, glued a speaker magnet to the inside of the lid and snapped it back on, voila - instant magnetic mount.

05-29-2002	#12 (permalink)
gcrocker Registered Member Join Date: May 2002 Posts: 31	Not that appropriate for stumbling (it's 20" high and PVC), but I may mount it on my crappy van for just that purpose: http://www.guerrilla.net/reference/a...r_omni_lowpwr/ First one I built took 3-4 hours, and I think I can do them in an hour now. -glenn

05-30-2002	#15 (permalink)
sykojester Net Lurker - phjear Join Date: Apr 2002 Location: Tallahassee, FL Posts: 371	just looked @ the pics (too busy to read everything else right now), but I know I wouldnt dare go out w/ it the way it looked. I thought it was nice and all, but man, that looked like a pipe bomb. LOL. esp all black.