Connectique Wifi - Outils antennes artisanales.

Outils de base pour fabriquer son antenne wifi...

Le minimum nécessaire...

Fer a souder 30w
Pinces, pincettes diverses
soudure, et fiche wifi rp-sma mâle
à sertir.
Cable wifi 50 Ohm
Mètre, règle ou encore mieux pied à coulisse.
Mini perceuse

Facutatif

Pistolet à colle
Multimètre - pour mesure tests continuité et  court-.circuit.
Pied à coulisse
Pinces a sertir
Marteau ??? pour se défouler...
Minutie, patience ..bonne vue..pas trembler...

                                                                                                          Fiche rp-sma male - Antennes wifi




Exemple construction Antenne wifi yagi Raptor2
Collecteur Anneau en Boucle Double polarisation Horizontal-vertical...



Essai avec Anneau et Double-ellipse   Voir test du mois
 


 Chien sécurité wifi




           Soudure de la fiche wifi RP-SMA male . Le plus délicat...
Excusez pour les photos mais j 'ai pas la macro...

 La fiche wifi a souder mesure 7mn de Long et 0.5mn en Diametre. Besoin de bon yeux...
 Support systéme "D".  L'etau support aiguille Wifi
Ps : ne pas trop serrer , l'embout réceptif est creux
 On dénude le cable wifi...





 
 
 On soude...pas pu me prendre en photo en trin de souder...Me manque une autre main...
NB: ici le + dur est fait.

 On enfile la fiche Rp-sma...On laisse deborder in peu de tresse de masse pour la continuité.

 On teste...Si on a un testeur...
Bonne photo profitez du zoom...





On fini a la pince a sertir...ou autre pince
de facon a ecraser la bague
sur le cable.


Cablage - Connectique
- Rallonges...Wifi

Le point faible de la wifi le cable...Souvent affaiblissement du signal au dela de 2 Métres..: pertes de 3-6 Dbi.

Dans la mesure du possible éloignez-vous de vos appareils wifi
par rallonges USB. Jusqu'a 5 Métres maximum
. Pas de perte de signal

Les cables sont utiles en cas d'utilisation de l'antenne en extérieur.

Cher au mètre : 3 a 5 € . Pour du bon câble a faible pertes théorique.

Ex : Rallonge de 2 mètres : 17.90 € TTC

 Le câble SMA LMR200 inversé vers type N allonge votre antenne sans fil de 2 mètres afin de lui offrir une localisation parfaite en extérieur

Reliez sans fil d'immeuble en immeuble des réseaux professionnels ou fournissez un acces Internet sans fil aux applications hot spot


Ce câble permet la communication sans fil en offrant des communications à faibles pertes entre votre point d'accès et l'antenne.

Fiche technique :
  • Compatible uniquement avec S506 antenne directionnelle extérieure 14 DB et S505 antenne ominidirectionnelle extérieure 8 DB
  • Compatible Wi-Fi avec les terminaux 802.11b/g 2,4GHz & 802.11a 5GHz pour étendre les réseaux sans fil.
  • Connecteur SMA femelle inversé vers type N mâle.
  • L'installation optimale de votre périphérique Wi-Fi actuel vous permet d'optimaliser ses performances sans fil.
  • Le conducteur extérieur flexible permet le plus petit rayon de cintrage possible à tous les câbles de taille et de performance semblables.
  • Offre des communications à faibles pertes aux antennes sans fil
  • Le blindage 50dB RF est de 10 dB supérieur au simple câble coaxial bindé standard (40 dB).
  • Le contrôleur externe multi-couche relié à la masse est estimé modestement à > 90 dB.
  • Conception étanche du câble pour une utilisation en extérieur avec les meilleurs matériaux pour une résistance aux UV
  • Câble gainé de polyéthilène conçu pour une utilisation en extérieur
  • Déploiement rapide et aisé dans un environnement WLANCABLE 2m POUR ANTENNE WIFI TRENDNET TEW-L202

  • Pour mes antennes..j 'utilise 2 modèles de cable...
    Nb:Pour des petites rallonges < 50 cm comme dans la plupart de montage d' antennes wifi,
    les pertes observées sur differents cables ne sont pas significatives...



    Quelques exemples...


    - CFD200 Voir toute les infos   Pertes théoriques constructeur :5 Dbi pour 9 métres..
    Atténuation à 2400 MHz,  0.55 dB par mètre

    Low Loss Coaxial Cable Construction

    - Rg 174 cable très fin a manipuler..

    Coaxial RG-174 (1 mètre)
    Câble coaxial 50 Ω RG-174.
    Diamètre externe 2.6 mm.
    Atténuation à 2400 MHz, 1.8 dB par mètre

    Autre exemple...

    Coaxial CNT-400 jusqu'à 6 GHz (100 mètres) Câble coaxial 50 Ω Andrew CNT-400 PE à très faible perte, le touret de 100 mètres. Diamètre externe 10.3 mm.
    Gaine sans halogènes.
    Ce câble convient aux applications 5 GHz et 2.4 GHz.

    Les produits Andrew sont d'excellente qualité. Les grands opérateurs de télécommunication utilisent principalement du coaxial de marque Andrew.

    Atténuation à 2400 MHz, 0,21.65 dB par mètre
    .
    Prix 229€ 100M.


    - Coaxial CNT-600 jusqu'à 6 GHz (305 mètres)
    Câble coaxial 50 Ω Andrew CNT-600 PE à très faible perte, le touret de 305 mètres.
    Diamètre externe 15 mm.
    Gaine sans halogènes.
    Ce câble convient aux applications 5 GHz et 2.4 GHz.

    Les produits Andrew sont d'excellente qualité. Les grands opérateurs de télécommunication utilisent principalement du coaxial de marque Andrew.

    Atténuation à 2400 MHz, 0,144 dB pour 1mètre.

    Voir la fiche produit du fabriquant


     Quelques Antennes wi- fi Yagi à construire...

    Yagi wifi 16 élements. 16 Dbi  pour carte usb Pci wireless






    Autres exemples modèles antennes...

    Antenne Yagi à 11 éléments
    + 2 réflecteurs latéraux


    Les 11 éléments sont alignés sur une règle en fibre de verre (2,7 X 10 mm) et le dipôle est légèrement décentré. la seconde moitié du dipôle est soutenue par une petite patte.
    La patte et les 11 éléments sont collés à la "super glue". Le réflecteur et son support sont collés à la colle époxy
    l'élément rayonnant est constitué de fil de laiton de 1mm, les 10 éléments parasites sont en fil de laiton de 0,8mm

    Cette une antenne est très facile à réaliser. Elle demande en revanche d'être très méticuleux sur certaines dimensions.
    Ses caractéristiques aussi bien pour le gain que pour le rapport avant/arrière la rende très intéressante. Pour un montage en extérieur on pourra la protéger dans un tuyaux PVC de 80mm.


    Remarquez l'évolution de la partie imaginaire de l'impédance...
    Cette particularité donne une remarquable largeur de bande.


    Amélioration: L'extension à 19 éléments... je vous livre déjà les diagrammes. Je l'ai montée sur la même latte en fibre de verre que la version 11 éléments.
     Elle souffre d'un problème de rigidité mais les premières mesures confirment ce que prédit la théorie.



    Détails du montage du connecteur
    Détails du raccordement au dipôle.
    Noter qu'une moitié du dipôle est fixée à la latte en fibre de verre (elle dépasse de 0,5mm) et que l'autre est collée sur une petite patte, elle-même collée sur la latte. Le dipôle est dissymétrique.
    /

     Tableau des dimensions
    Version à 11 éléments
    Longueur Entre-axe Diamètre Remarques
    60.4mm 18mm 0,8mm réflecteur
    58mm 8.6mm 1mm élément rayonnant
    52.6mm 30.6mm 0,8mm 1er directeur
    50mm 30.6mm 0,8mm ...
    48.8mm 30.6mm 0,8mm
    48.2mm 30.6mm 0,8mm
    47.6mm 30.6mm 0,8mm
    47mm 30.6mm 0,8mm
    46.4mm 30.6mm 0,8mm
    45.8mm 23.8mm 0,8mm
    42.6mm 0,8mm
     Version à 23 éléments
    Longueur Entre-axe Diamètre Remarques
    61.2mm 20mm 0,8mm réflecteur
    57.6mm 9.2mm 1mm élément rayonnant
    52mm 32.5mm 0,8mm 1er directeur
    51mm 32.5mm 0,8mm ...
    50.7mm 32.5mm 0,8mm
    50.4mm 32.5mm 0,8mm
    50.1mm 32.5mm 0,8mm
    49.8mm 32.5mm 0,8mm
    49.5mm 32.5mm 0,8mm
    49.2mm 32.5mm 0,8mm
    48.9mm 32.5mm 0,8mm
    48.6mm 32.5mm 0,8mm
    48.3mm 32.5mm 0,8mm
    48mm 32.5mm 0,8mm
    48mm 32.5mm 0,8mm
    48mm 32.5mm 0,8mm
    48mm 32.5mm 0,8mm
    48mm 32.5mm 0,8mm
    47.7mm 32.5mm 0,8mm
    47.4mm 32.5mm 0,8mm
    47.1mm 32.5mm 0,8mm
    46.8mm 32.5mm 0,8mm
    40mm 24mm 0,8mm

    les 2 réflecteurs latéraux (70mm X 115mm) sont inclinés à 45° et l'extrémité arrière est alignée sur le brin réflecteur, 52 mm sur le coté.
    Encore une fois, soyez très précis...forez la latte en fibre de verre avec la bonne mèche, bien perpendiculairement et en respectant scrupuleusement les écartements
    (surtout pour le brin réflecteur, le 1er directeur et le dernier).
    Pour avoir la bonne longueur, j'ai coupé chaque élément trop long et je les ai raccourcis ensuite à la lime. L'utilisation d'un pied à coulisse n'est pas du luxe. ..



    • Outils
    • Scie
    • Cutter
    • Tenaille
    • Colle
    • Lime
    • Règle
    • Pied à coulisse
    • Perceuse
    • Précision et patience...

    Materiels


    - Coaxial 50 ohms > RG58 OU CNT195 (le CNT 195> moins de perte en décibels)

    - Connecteur RP-SMA qui viendra se fixer sur le coaxial.Afin de le brancher sur votre carte wifi.

    - Un tube plastique (comme sur la photo) diamètre 10mm x longueur 650mm. Ou une règle plastique (creuse ou pleine) largeur 18mm, épaisseur 13mm, longueur 650mm.

    - OPTER POUR LA REGLE PLASTIQUE si vous etes un newbie en brico,ça vous aidera...

    - Une tige de laiton ou acier de diamètre 2.5mm (voir 3mm),longueur de 1mètre (le laiton,c'est mieux!).

    - Rectangle de cuivre ou acier: longueur 12mm,largeur 4mm,épaisseur 1mm (le cuivre c'est mieux!).

    Fabrication

    • Tracer sur la règle en plastique (coté 13mm) les intervalles(A>z..Z>B...B>C...).Voir plan.
    • Percer bien droit au centre de chaque intervalle.(Percer sur toute la largeur des 18mm).>15 trous.
    • Couper la tige de "laiton" en segments (A,B,C,E...N,O) à la longueur demandée sur le plan.
    • Insérer les segments dans les trous "à leur place",les centrer.(un point de colle).
    • Fabriquer l'éllipse avec le rectangle de "cuivre" 12x4x1mm,voir plan (cotes) ellispe.
    • Placer l'éllipse à "Z" (sur la largeur 18mm),centrer et coller.
    • Prendre le coaxial,le faire tenir avec des colliers plastique. Souder à chaque extrémité de l'éllipse la masse (tresse) et le +.

    Coût de fabrication
    • Coaxial: RG58 > 0.50 euros le mètre / CNT-195 > 1.50 euros le mètre
    • Connecteur: RP-SMA > 3.50 euros
    • Tube ou règle plastique: 1.50 le mètre
    • Tige de laiton: 2euros le mètre.
    • Rectangle (pour fabriquer l'ellipse)> récupération,ça ne se vend pas!

    TOTAL: une moyenne de 8 euros.




    Voir modèles Yagi wifi Backtrack


    http://wiki.backtrack-fr.net/index.php/Yagi


    Cartes Wifi et antennes compatibles Backtrack 3




    SECURITE

    Backtrack Surveillance réseaux - test clés wifi sécurité -clés codage wifi, donc les protocoles WEP et WPA...


    A lire :

    Ici trés beau tuto : bien détaillé bonnes photos...

    Comment fabriquer une antenne Wifi soi même, facilement et surtout pas cher ?
    Vous n’avez pas de connaissance dans l’électronique, vous êtes passionnez pour l’informatique, le Wifi et les technologies de communication, ce tutorial est pour vous !
    Voila comment se composera le plan :
    1) Capter les Réseaux sans fil avec une antenne Pringles
    a) Fabrication de l’antenne Pringles
    b) Fabrication du câble
    c) Carte PCI et connecteur SMA
    2) Capter les Réseaux sans fil avec une antenne Ricoré
    a) Fabrication de l’antenne Ricoré
    3) Comparaison Pringles et Ricoré (NetStrumbler)



    Le problème le plus courant est la non compatibilité de votre carte wifi avec Backtrack :(   Si vous prévoyez d'investir, voici une carte wifi usb compatible et tout à fait abordable : la D-LING-G122 .

     


    Pour les personnes voulant pousser la chose plus loin je vous propose la carte wifi usb Alpha AWUS036H qui permet le fixement d'antennes.

    Cette carte est considérée par la communauté comme excellente et relativement abordable.  Elle est tellement puissante qu'elle est………bon disons interdite en France ;)

    Vous pouvez la trouver sur le Net en fouillant un peu à l'international et vous en sortir pour environ 50€. Son grand avantage en dehors de sa puissance et de pouvoir fixer des antennes.

    La première est une antenne omnidirectionnelle 9dbi pour arroser tout autour de l'ordinateur (20€).

    La deuxième, la plus intéressante est de type Yagi et permet de capter à plus de 200 mètres (en théorie 1,3 km). Cette dernière coûte 34 € et permet de viser un point comme "un sniper wifi".

     


     


    Lincomatic's Homebrew WiFi Antenna



    One of my latest obsessions is building homebrew WiFi antennae.

    Heinz Beans Cantenna

    This is the first antenna I built. It's the ubiquitous circular waveguide "cantenna":






    I obtained my can by going to my local 99 Cents Only store and buying a can of Heinz beans, which happened to be desired 3.25" diameter. The resultant methane gas produced from consuming the beans was used to power my soldering iron afterwards.

    I will not go into the construction details, as they are very well documented on Greg Rehm's site. Finding his online cantenna calculator rather intriguing, I set out to find the mathematical roots to his calculations. The result is my own cantenna calculator program, which I wrote in in C++, based on formulae obtained from the ARRL Antenna Book. It's available on my free software page; the archive contains both a Win32 console-mode EXE and full source code. In addition, Adam Lesser has kindly supplied a binary for OS-X.

    Greg Rehm's calculator fixes the operating frequency at Channel 6 (2437MHz), which is the center channel in the USA, giving the best tradeoff if you want to build a general purpose antenna which works across Channels 1-11. On the other hand, my calculator lets you tune your antenna for maximum gain on a specific channel; this is handy if you want to use your antenna set up a permanent point to point link. Let's go through an example using my calculator. The syntax of the program is

    cantenna diameter centerchannel

    where diameter is in mm. So to make an antenna optimized for Channel 6 using my 3.25" (82.55mm) diameter can, we would invoke it as follows:

    D:\>cantenna 82.55 6
    Lincomatic Circular Waveguide Calculator V1.1 (Feb 25 2004 23:03:31)

    Waveguide diameter: 82.550000 mm (3.250000 in)
    Channel: 6 (2437 MHz)

    TE11 Cutoff (MHz): 2128.387692
    TM01 Cutoff (MHz): 2779.953846
    Guide Wavelength (mm): 252.566154 (9.943549 in)
    Operating wavelength (mm): 123.017012 (4.843189 in)

    1/4 Guide Wavelength (probe to back) (mm): 63.141539 (2.485887 in)
    Probe Length (mm): 30.754253 (1.210797 in)

    probe pos (Ch1): 66.046774
    probe pos (Ch11): 60.564048
    probe pos (Ch14): 58.520674
    difference between Ch1-Ch11 (mm): 5.482725


    So what's the meaning of all this gibberish?  The probe should be 30.8mm (1.21") long, and should be set 63mm (2.5") from the inside of the back lid of the can.  The operating wavelength of 4.8" shows us that we don't have to worry that the sides of the can have ridges, because the their depth is insignificant compared to the wavelength our signal. The Guide Wavelength is the wavelength of our waveguide. The TE11/TM01 Cutoff frequencies give us the approximate upper/lower frequencies of operation for our antenna. Since Channel 1 is centered at 2412MHz and Channel 11 is centered at 2462 MHz, we have a comfortable margin. Now the interesting part is that if you wanted to tune the waveguide for the center frequency of Channel 1, you would use a probe distance of 66.04mm instead, and for Channel 11, you would use 58.52mm. What this means is that there is a whopping 5.48mm difference in the optimal probe distance between Channels 1 and 11, so if you are going to use the antenna on a fixed channel, it's better to enter than channel number instead when running the program.

    Experimenting with my calculator program, I've found some interesting information. As the waveguide diameter increases, the difference in optimal position for the driven element between Channels 1-11 drops.  I tried upping the diameter iteratively until the TM01 cutoff frequency started to go too low to do Channel 11. From my studies, it seems that about 92mm is the optimal diameter for the waveguide if you want to try to optimize it for flattest response across Channels 1-11; this is because it minimizes the difference in the probe position between Channels 1-11 -> about 2.63mm, so the SWR curve across the WiFi band is flatter.

    Contrary to popular belief on the Internet, a can length of 3/4 the waveguide wavelength is not optimal. The ARRL Antenna book recommends 2-3 waveguide wavelengths instead. I've found that adding more cans indeed increases the gain. A 4-can one is the longest I tried; I didn't write down the gain testing results, but it was considerably better than the 1-can antenna. Adding more cans helps launch the standing waves in the can better. bmoore314 has some excellent info in this Netstumbler.com thread, including info about adding a conical collector to it.  My results from experimenting with a conical collector are documented in the section about my Bazooka Cantenna.


    Toothpick Monopole

    This is my first attempt at designing something myself. I downloaded the EZNEC demo from www.eznec.com and started fiddling 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 wavelength 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). Below are plots of my EZNEC model:



    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).

    Comtelco 7.5dBi Patch Antenna Clone

    This antenna has a page of its own.


    Mobile Mark 5dBi Ommi Clone

    The Mobile Mark 5dBi antenna is the stumbling antenna of choice used by many Netstumblers. outcast_one was kind enough to post some pictures on the Netstumber.com website which were clear enough to get measurements from. Hope he doesn't mind my re-posting them here:



    From the above photos, I estimated the dimensions below:
    • wire: ~1.5mm OD
    • ground plane to coils: 34mm (9.5mm of that is under the black plastic bump..wonder what's in there?)
    • length of coils: 13mm
    • coil ID: 5mm
    • coil OD: 7mm
    • coil spacing: ~3-3.5mm
    • coils to top: 51.5mm+13mm(plastic tip)..wonder how high the wire goes into the tip.
    Here is my implemenation alongside my toothpick for comparison:



    I used solid copper wire cut out of a piece of Romex...I forget the gauge..it was all I had available; tried initially to bend a coat hanger but the steel wire was too difficult to bend into the coils. Once again I used a 3.25" can lid as the ground plane; this is close enough to Mobile Mark's specified 3" ground plane. A nicer implementation would be to use a discarded hard disk platter (kudos to sparafina for that idea). I am worried that the copper is too soft to stand up to high winds when attached to my car. When I get a chance I will either encase the whole whip on a plastic tube or just support the coil by inserting a suitable piece of plastic into it. Another idea is to just fill the coil with hot glue.

    My initial tests were not that promising...the gain was about the same as my toothpick, except that the antenna seemed less sensitive to polarization. However, stumbling with the antenna has shown that on the average, I pick up AP's 1-2 car lengths farther away than with the toothpick, and the SNR is often a little higher. Therefore, this antenna is used in my current stumbling rig.

    Trevor Marshall's BiQuad

    Trevor Marshall has posted plans, as well as NEC2 models for his biquad dish feed. The antenna can also be used standalone.



    I fashioned the reflector from a discarded tin can. The reflector is 123x123mm, with 30mm "lips" as specified by Trevor for standalone use. The driven element is composed of copper wire I got out of a piece of Romex, with 30.5mm legs, and is suspended 15mm above the reflector. The antenna as pictured above was a complete failure and had horrible performance. Trevor explained to me via e-mail that I messed up the feed (the photos on Trevor's site are grainy). Here is my revised feed:



    Instead of rigid coax as specified by Trevor, I just used some more copper wire for the connections; I'm not sure how this affects VSWR, but the antenna gave me about 3dB more gain than my Comtelco patch clone during my initial tests.

    Bazooka Cantenna

    I've been trying to hook up my brother, who is a professor at a local college to his campus network. He lives just on the edge of campus, and although the IT Dept. has discussed putting an AP on his side of the street, no progress has been made for several months. Therefore, I decided to take matters into my own hands. There are tons of AP's just around the corner and out of LOS from my bro's house, but his block is strangely completely devoid of any signal.

    Finally, one day I climbed up on his roof to see if I could get LOS and a signal from a yagi on a hill which was pointed away from my brother's house. I used my ORiNOCO card in my Jornada, pointed my biquad through a tree, and amazingly got a 5dB SNR! Now we were in business, but the 5dB seemed a little too weak for reliable communications, especially with the chance of the tree growing denser foliage.

    I decided a cantenna might be the way to go, so I built a new one using 3 3.25" diameter cans...this makes the total length about 1.75 waveguide wavelengths. The driven element is 30.75mm long and mounted the 64mm from the back of the can. The conical collector is 7.25" in diameter on the big side, w/ a 30degree flare. This was just a quick prototype so I made the collector out of 2 coat-hanger circles, separated w/ four 4" long coat hanger supports covered in aluminum foil. the final design will need to be more durable to stand up against wind & hail. Here is what it looks like:



    Before trying it on the target site, I did some testing with my AP at home. Here are the SNR's I got across the street from my AP:

    ORiNOCO built in: 26 dB
    2 cans w/o collector: 36 dB
    3 cans w/o collector: 37-38 dB
    Trevor Marshall biquad: 39 dB
    3 cans w/ collector: 43 dB (!)

    This is the highest gain antenna I've built yet. In my excitement, I dragged my Jornada off a table while connected to this %$* thing and it fell on the floor. Lucky the card & Jornada are ok, but I broke off the end of my pigtail.

    The next morning, I climbed on my bro's roof armed w/ the bazooka cantenna. Going back to the same place I got the 5dB SNR w/ the biquad, the bazooka got 8dB. I fired up PocketIE on the Jornada, and was able to surf a little - paydirt! Since it was daylight this time, I was able to try out more places on the roof, and finally found one clear of the tree which yielded 12dB SNR. Now we're in business; I've got a little more margin to play with so when I hook up the long LMR-400 cable to get the signal inside the house I won't get killed by attenuation.

    To be continued after I get the rest of the equipment to complete the setup...

    In the meantime, I played with the bazooka from the deck of my hillside house, and was astonished to find that it picked up an AP I'd detected while stumbling on the freeway in my car (using my Mobile Mark clone on the dash). Plugging the GPS coordinates in from the freeway into Microsoft Streets & Trips, it turns out the AP is about 4 miles away! Using the bazooka on at my house, the SNR was 8dB (signal ~-88dBm). As a comparison, I also tried the biquad. Using the biquad, the signal is unstable w/ max 4dB SNR, and it catches the AP for only a second at time.

    Collinear Omni

    This antenna has a page of its own.


    guerilla.net/Lucent/Maxrad Collinear Omni



    Although I have been aware of the guerilla.net low power collinear omni for some time, I have hesitated to build it due to its complexity, and the fact that I didn't fully understand the design. To complicate matters, the website has been down for several weeks, making the design inaccessible. I was finally able to piece it together by using a copy from google's cache, and archived JPEG's from this site: http://www.tux.org/~bball/antenna/. My google searches also yielded an attempt to explain the theory behind the antenna.

    Although the guerilla.net folks claim that the antenna is their own original design, one day while surfing the FCC site for information about Lucent's ORiNOCO cards, I happened upon an interesting document. On page 13 of this document was a photo of antenna labeled Maxrad which looked almost identical to the gnet collinear omni. sparafina of the NetStumbler Forums did some initial analysis of this antenna, and found its dimensions to be very similar to the gnet design. Later, I found a test report which refers to the antenna as external antenna AUO24-OD-10, and lists its gain as 10dBi. Once I sat down to build the antenna from gnet's design, I found their description of the coil dimensions to be confusing - maybe I am just too dense. My initial attempt was a complete failure with very little gain, probably due to my confusion over the exact dimensions. Therefore, I decided to try again, but this time building it based on measurements taken from the FCC photo. Below is an internal photo from the FCC archive which I've modified to ease the estimation of the measurements:


    click on photo for larger version

    The photo is rather blurry and pixellated, but I've sharpened it a bit to increase clarity. If you'd like to check my measurements, an easy way to do it is use Paint Shop Pro on the larger version of the photo. Simply use the selection tool to cut out a piece of the ruler. Then you can use the selection as a ruler by dragging it around the photo. For vertical measurements, rotate the selection by 90 degrees. Very handy indeed. Not only is the photo blurry, but the quality control on the antenna appears to be deficient; from segment to segment the measurements are not identical. Here are the measurements I estimated from the photo:

    • Coil wire diameter: 1.5mm
    • Coil OD: 6mm
    • Coil pitch: 3.5mm center to center
    • Tube diameter: 3mm
    • Tube length: 56.5mm
    The main difference between the gnet collinear and the Maxrad is just the wire diameter. The gnet design uses 3/64" wire (which is alot easier to bend) and 3/32" tubing. Also, the gnet design specifies to leave a 2cm tail on the coils, which I found to be a little too short. Otherwise, the two designs are pretty much identical. Since guerilla.net seems to be down, I hope they don't mind that I've reconstructed their page as best I could for your convenience.

    Since I already had the tubing and wire from the gnet parts list, I used 3/64" wire and 3/32" tubing instead. I think the 2:1 ratio of tube to coil diameter is more critical than the actual diameters anyway. Since the Maxrad decoupler is hidden in the plastic, I used the gnet dimensions for the decoupler, but substituted a N-female jack for the SMA jack.

    For those who don't feel comfortable cutting and bending the parts, aerialix sells the antenna in kit or assembled form. Their prices are very reasonable.

    Parts List

    Below is the complete parts list with prices I paid:
    • (2) 12" long 3/64" diameter brass rod 2x$.59
    • (2) 12" long 3/32" diameter brass tube 2x$1.09
    • (1) 12" long 11/32" diameter brass tube $1.99
    • (1) 2ft long 1/2" diameter PVC pipe $0.10
    • (1) 1/2" diameter PVC end cap $0.29
    • (1) N-female panel jack $4.50
    Grand Total: $11.50 including tax. Everything except the N-jack was bought at Osh Hardware. It's a good idea to buy 1 extra piece each of tubing and wire in case you mess up. I used Schedule 50 pipe because it's the thinnest (I'm paranoid about losses through the radome).

    Construction


    measurements

    Below is my assembly procedure:

    NOTE: Try to be as accurate as possible in cutting the parts and spacing them during assembly. .5mm accuracy is difficult but at least try to get within 1mm of what's specified. Otherwise, you may be sorely disappointed with the performance of your finished product. I used a pair of vernier calipers extensively during the construction of this antenna.
    1. Hold a piece of 3/64" brass wire against 9/64" drill bit and wind 4 turns, each turn separated by about 3.5mm. Leave about 10mm of straight wire before the turns and 24mm after the turns. Adjust the spacing of the turns with needle nose pliers while the coil is still on the drill bit. Bend the ends neatly with the needle nose pliers. Repeat until you have 4 coils.
    2. Cut four 57mm long pieces of 3/32" tubing and one 91.5mm long piece. I used the cutter on a pair of needle-nosed pliers to cut them; this flattened them, which is not bad because the hole in the tubing is actually a loose fit. Next, I used the needle-nosed pliers to squeeze the tubing until the hole opened up large enough to pass the wire into it. Finally, I filed the tubing smooth, which took off about .5mm off its length.
    3. Cut a 30mm piece of 11/32" brass tubing. I used a hacksaw and mitre box.
    4. Solder the 91.5mm long tube to the center pin of the N-jack. This is the feedline
    5. Slip the 30mm tube over the 91.5mm tube, and solder to the N-jack. This tube is the decoupler. The feedline must be supported in order to keep it from shorting on the decoupler; I slid a piece of rubber hose over the feedline.
    6. Solder a coil to the feedline, leaving about 3mm of wire between the feedline and the start of the coil.
    7. Solder a piece of 3/32" tubing to the other end of the coil, leaving 22mm of straight wire between the last turn and the tubing.
    8. Repeat until you get to the top of the antenna.
    9. Cut the PVC pipe to the proper length to enclose the antenna and glue on the end cap.
    10. Cut pieces of foam to support the antenna inside the PVC pipe - I stuffed the foam into the coils - and carefully slide the antenna into the pipe.
    11. Attach the N-jack to the other end of the pipe. You can screw it onto a flat end cap if you can find that style. I chose to just tack the N-jack directly to the pipe with hot glue. Then, I used epoxy over the hot glue for strength and heat resistance.

    decoupler


    nude antenna


    completed antenna in radome

    Performance

    I tested the collinear down the street from my AP using MiniStumbler. Below are the results:

    AntennaSNR
    ORiNOCO built-in:10 dB
    collinear:20 dB

    For some reason, the signal strength was fluctuating wildly, so this is the best estimate I got. Overall, I'm pretty happy with it, which is good because this antenna cost more and took by far more time to build than anything else I've made to date.





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