how to build an omnidirectional antenna?

Configuration and other hardware related information

how to build an omnidirectional antenna?

Postby Guest » Mon Mar 18, 2002 11:43 am

I have found a few instructions on how to build a directional antenna, but I'm not too sure of how to go about building an omnidirectional one.
Can anyone point me in the right direction?

Postby Guest » Mon Mar 18, 2002 12:22 pm

I guess I've answered my own question. I'll try with these instructions.

antenna construction

Postby Guest » Mon Mar 18, 2002 6:00 pm

Follow the designs on guerilla net's website. However, do not use BNC or PL-259 connectors (what this person thinks is a N connector) Both of the connectors he used are not suitable for 2.4 ghz operation. If you must use Radio Shack(crap) get TNC connectors. They are the only ones you will find there that will work. Better yet, order a few N connectors online.

Postby Guest » Mon Mar 18, 2002 7:22 pm

I built 2 this weekend from the directions I found here.. ... ni_lowpwr/

I sub out the connectors that they used for a panel mount N female.
Now just waiting for my pigtail to arive. Ill try to get picts (step by step) of the next ones I do and post them some where.

Mobile omni

Postby Guest » Tue Mar 19, 2002 2:31 am

Hi there,

depending on the type of omni you want, have a look at the mobile omni at

The main problem with stacked antenna's like the colinears is feeding them efficiently. As the antenna length and number of elements is increased, the signal being fed into the radiator descreases etc.

So when you see a 1.1m long antenna with say 10db gain, and a 2m long antenna with 11db gain, this is why.....



Postby Guest » Tue Mar 19, 2002 4:21 pm

I'm in the process of building the antenna now.
The hardes part seemed to be making those coils - I used a sheetrock screw, but still they all turned out quite crooked.
I part that was not so easy to find was the reverse polarity type n connector which i found at
I need that type of connector to attach the cable that came with my enterasys system. $12 each.
Now I don't even know if I will be able to fit feedline onto the connector since the instuctions are for a smaller connector. We'll see.
I have questions:
Why do you need the coils? Does anyone explain where they get all those measurements from (apart from the wavelength which is pretty clear).
Why do you need a decoupling tube?

Postby Guest » Wed Mar 20, 2002 5:47 am

The coils are "loading coils." For a complete explanation, as well as some of the real detailed formulas, get the ARRL book on antenna design. I believe that is probably where B. Oblivion got his figures. I haven't read that antenna page in some time, but I recall some info there or on the original l0pht site which lead me to believe that he is ham.

Same thing on the decoupling tube. The tube is used to match impedance in the coax cable to the antenna. For the details, look in the ARRL antenna book or some other books on antenna design.


Postby Guest » Tue Mar 26, 2002 4:37 pm

i have the arrl antenna book now. holy cow. to validate/ modify the construction spec from the guerilla site with the help of this book seems like quite a task.
i wonder if someone knows what they based their constuctions designs on.
( ... ni_lowpwr/ )

that's the one i'm talking about.
the problem is that i will have to use bigger connectors at the end because i want to connect it to an enterasys ap wich comes with reverse polarity n connectors.
I have no idea if the feedline or the decoupler will have to be modified for this connector.

Postby Guest » Tue Mar 26, 2002 5:13 pm

N connectors, reverse polarity N connectors, SMA, etc. are all 50 ohm impedance, so you should be able to use the same decoupler design. The decoupler matches the impedance of the antenna to the impedance of the line. From the looks of that design the SMA was chosen due to its size. You know, you can have the SMA on the antenna end, and have the RP-N on the AP end.

Keep reading! You'll figure this stuff out in a while. You may also figure out that it is just easier to order an antenna from a manufacturer. ;-)


Decoupling stubs..

Postby Guest » Fri Apr 05, 2002 10:29 pm

Aside from matching the impedance of the antenna/s, decoupling stubs also keep stray R.F. off of the feedline coax running into the antenna.

It reduces the felt R.F. on the shielding/braid of the feed cable and also provides a groundplane circuit as well.

Since the antenna in this thread is a collinear design, the feed is in the base only and is NOT of the "corporate" feed design used by Decibel, Celwave, Kathrein for their products.

Corporate feed structure positions the actual feed point near the physical center of the radiating elements, and this method allows the R.F. to be delivered to every integral element equally. This also gives a better radiating pattern, tilt and E/H plane patterns as well. It also maintains a better 50 Ohm impedance match to the transmitter which keeps
intermod products from being generated by corroded/exposed connectors, matching stubs/tuners and the like. Internal matching/feeds keep this "important" portion of an antenna out of the elements and provides a longer lasting antenna service life(theoretically, that is).

Postby Guest » Fri Apr 05, 2002 11:17 pm

Are you a Ham or an RF engineer? (or both!) You obviously know the theory very well. I have my Tech ticket; and someday soon I'll finish getting my code up to speed and take some more tests...

You'll find that there aren't too many on the NS forums who have much RF knowledge. In fact there are propably just a half-dozen or so.


Decoupling stubs and....../?/

Postby Guest » Sat Apr 06, 2002 12:01 am

Yes, I work in R.F. daily maintaining and building UHF repeaters I own in my state and in MN as well.

My call is ka9uce, and I've been a "tech" since 1983, with no desire to "advance" up or down to an advanced "class".
Since I hate H.F. why take a test for bandwidth I'll never make use of?

I also rebuild commercial antennas for resale as well as my own use. Take apart a Decibel 812-F-X 800 Mhz. antenna if you get the opportunity, they are filled with UT-141 cable for antenna projects and more(I have tw, one good, one for parts)!
I was hoping to use NS with my Proxim Symphony cards I have for a micro-net in my home/shop, but alas, they don't work with NS, so now I am off to find an Orinoco silver WLAN card so I can war drive with my Compaq LTE5300.

I find the Proxim cards "appear" to be Prism chipsets which don't work with NS<sigh>.

And yes, I do have my call listed on QSL.NET for my AO-14 satellite work<grin>.
ICQ#: 24800907 if you want to "Q" me sometime, be my guest, but please, NO BOTS, they never allow "authorizations" through ICQ for some reason.

Postby Guest » Sat Apr 06, 2002 11:53 am

My call is KB1CPS. After umpteen years of fiddling with electronics and radios I finally got it in '98. Since then I only worked 2 Meter a little. Some of the of the guys I know that work HF tend to be real bigots about the classes. Kind of "If you don't work CW, you're nuthin..." Their attitude is something of a pain. It's always been a "when I get around to it" for me. In the meantime, I'm having fun with this unlicensed microwave & computer stuff.

In the past, I've done some work in with both VHF & UHF for public safety agencies. About ICQ, I've never tried it. The satelitte work sounds interesting; I'll look up what you've done.


Ham related activities....

Postby Guest » Sat Apr 06, 2002 12:52 pm

That site( has nothing I have done with satellites, it is mainly used as a contact point for those that have made contact with me via UO-14, nothing more really.

I also sold all my "ham" gear and put amateur radio on hold until I can find a nicer group of people to associate with.
N. Wisconsin has a small group of close-minded hams that "expect" you to at, say and think as they do, I do NOT fit that picture, so I am the outcast(too bad for them, they lost two 440 repeaters because of this also).

I hate snobs and that mentality/attitude, it's NOT conducive to good will and friendship. Even when they KNOW you are listening, they will not call you back, even if you place a general(CQ) call for some conversation, they completely ignore me and several others I associate with. They'll wait a few minutes, thinking I've moved on, then call their buddies to meet for coffee.

The group I refer to is: Tomahawk Repeater Association, of Tomahawk, Wisconsin. The 145.430 repeater, and it's many members are thoughtless snobs(to me at least, they are) and only care about "you" if it places them in the spotlight showing that they are so good willed and caring(NOT!).
They are the MAIN reason I gave up on amateur radio, because I happent to live near this group, and I refuse to be a moldable puppet for their amusement.

Try ICQ, go to TUCOWS.COM and download the beta version for your platform. It's easy and you can create a list of folks you would like to stay in contact with.

Hope to see you pop up in my list, we can use real time instead of list postings.

I'll be looking for an Orinoco card to supplement these crappy Proxim Symphony cards I am using.
I would like to USE NS instead of having it take up HD space.

ADIOS and:

SMA connectors

Postby Guest » Wed Apr 10, 2002 9:15 am

Just got my SMA connectors from DigiKey today (part# J608-ND) for the antenna design at ... ni_lowpwr/.

Jeez, these things are tiny. I thought they were going to be big, like the connector on my Fab-Corp antenna. How do I get from this connector: ... 2-0701-231

to the Orinoco connector on my card, or to the MCX connector on my SMC access point? Will I get losses if I use a standard pigtail and some kind of adapter? Should I make up a custom cable (like I can do that without soldering my fingers together).

It's hard to believe I'm a ham.


Return to Hardware

Who is online

Users browsing this forum: Exabot [Bot] and 7 guests