Specializing in
Long Distance
Wireless Networking.

Home
Up
Cables & Connectors
APs & Cards
Amplifiers
Netstumbler Kits
LAN Parts
M'nM Kits
Weatherproof AP
Power Over Ethernet
Masts & Accessories
ADSL Sharing
Recommended Reading
Ordering & Shipping
Successes & Testimonials
FAQs
Contact Us
Become a Reseller
Installers
Bicton FreeNet

   The AntCaptenna-II (12+ dBi)

    Introduction
    Design
    SWR test
    Link tests
    Prices

Introduction

The AntCaptenna (ACA) was born from a desire to make an antenna that:

bullet

could be used as a 'client' antenna (i.e. used to connect to an AP)

bullet

had a reasonable gain (12-14 dBi)

bullet

was waterproof

bullet

was rugged

bullet

could be pole-mounted

The result was the AntCaptenna - which gets its name from the Ant-Cap used as the back reflector.

[Ant Caps are used on wooden stumps in Western Australia, to prevent white ants (termites) from coming up from the ground into the house. The ant cap used here has a center section of 125x125mm that is flat, and has 50mm 'wings' that are bent 'inwards'. The total size is approx 225x225. I have absolutely no idea if the wings add or subtract to the overall performance of the antenna, but they look important! If you can't buy an ant-cap, just make a piece of galvanized metal approx 0.4mm thick, 150 x 150, or bigger.]

While the full instructions for building your own AntCaptenna are given below, you can buy some of the harder to get parts, or completely assembled AntCaptennas here .

 


 

Click image to enlarge

 

The Design

There is no new science in this antenna. It is nothing more than a BiQuad - ready for external mounting.

Note:

The original AntCap design specified a 15mm offset between the antenna element, and the back reflector. This dimension came from Trevor Marshall. This has always worried me, as that is 1/8th of a wavelength, and 1st principle physics says if you want a reflected wave to be in phase (i.e. constructive interference) then the reflector should be an odd number of 1/4 wavelengths. However - I trusted the "1/8" design.

I decided to put theory to the test and built a range of AntCaptennas with offsets ranging from 15 to 35 mm. The best RX signal level was at exactly 30.5mm (1/4 wavelength) and the peak was 4dB higher (better) than the 15mm (original) version.

The chart at left shows the peak value (-61 dBm) at 30.5 mm offset.

 A 4th-order polynomial of best fit is also shown.

So the conclusion is: Best offset = 30.5 mm = 1/4 wavelength

SWR Test

The SWR of the BiQuad PCB (alone, in free space) was measured as shown.

The minimum SWR falls nicely within the 2400 MHz WiFi band.

The Cookbook

Ingredients

bulletMy apologies in advance to those that have no access to these suppliers. They are places generally available in Australian capital cities.
bulletAll dimensions in mm. (unless otherwise stated)

 

Item Description Supplier Part Qty
1 AntCap 125x125x50 Bunnings 1079234 1
2 Bracket ("Angle-Pergola 88x63x36mm") Bunnings 1071032 1
3 M4x20 screws (pack of 20) Bunnings 643277 4
5 1/8" or 3mm  rivets Bunnings   4
6 Tube of flexible, waterproof caulk Bunnings   1
7 V-clamp (size to suit pipe) Jaycar LT-3235 1
8 Enclosure, IP65 rated, 115x64x40x3 Jaycar HB-6122 1
9 PCB Standoff, Adhesive, 6.35mm Jaycar HP-0760 1 pk of 25
10 Plastic cable tie, (small) Jaycar   1
11 N-connector, jack, RG58, crimp Prices   1
12 9006 low-loss coax (RG58 size) Prices 9006 0.4m
13 PCB, BiQuad Prices   1
 

Tools

bulletDrill
bulletDrill bits (3, 4, 5 mm)
bulletScrewdriver
bulletSoldering iron
bulletRivet gun

Method

  1. Enclosure Holes
    bulletDecide what polarization antenna you want to make. The pictures above show a Horizontally polarized antenna (the enclosure is up and down) to be mounted on a vertical pole. A Vertically polarized antenna would have the enclosure going sideways.
    bulletLocate the bottom of the enclosure. The bottom is the one with the groove for the gasket strip.
    bulletInsert the supplied gasket into the groove in the enclosure bottom. The gasket is too long; cut as needed.
    bulletPlace enclosure bottom in the center of the front of the AntCap. Align enclosure to be 'square' with the AntCap sides, and to match the polarization you want.
    bulletDrill 4 x 4mm dia holes (one in each corner of the enclosure) through the AntCap.
  2. Attach Bracket To AntCap Side
    bulletPlace short arm of Bracket against the back of one of the 4 'sides' of the AntCap, so that the end of the short arm aligns with the edge of the AntCap, and it is roughly centered along the AntCap side. Note: The bracket purchased from Bunnings has 4 small and one large hole pre-drilled on each face.
    bulletMark the location of the 4 small holes. Drill 3mm holes through the AntCap sides at these marks.
    bulletRivet Bracket to AntCap.
  3. Enclosure Top
    bulletLocate the top of the enclosure. The top has 4 brass mounting nuts embedded in the plastic (these are NOT the ones at the corners; they are 'inside' the enclosure.
    bulletUsing a hot soldering iron, remove and throw away each of these embedded nuts. Insert soldering iron into the nut, and gently rotate it out as the plastic starts to melt.
    bulletDrill a 5mm hole (for the coax cable) in the side of the of the enclosure top that will face down. The hole should be approx. centered in the enclosure face.
  4. BiQuad PCB
    bulletCut PCB as shown in the figure. [tba]
    bulletDrill holes in the PCB as shown in the figure. [tba]
    bulletAssemble the N-connector onto one end of the coax cable.
    bulletRemove 5mm of external insulation of other end of coax. Separate and fold back the shield. Remove 4mm of internal insulation. Twist the shield so that it resembles a piece of wire than can go through one of the small holes in the PCB. You may have to use only 50% of the shield wire or it ends up too thick. Solder the shield braid together to form the 'wire'.
    bulletThread the un-terminated end of the coax through the 5mm hole in the enclosure top.
    bulletPass the ends of the coax through the two small holes in the PCB, from the 'back' side to the 'solder' side. Solder the two ends of the coax to the PCB tracks.
    bulletUse a cable tie through the two holes near the coax, and tighten onto the coax.
    bulletInsert 3 plastic standoffs into the PCB, from the 'solder' side to the 'back' side.
    bulletApply a dap of caulk to the coax, just near the PCB. Make sure it goes all around.
    bulletRemove the protective paper from the 3 plastic standoffs
    bulletSlowly pull the coax so that the attached PCB moves into the correct position in the enclosure top, with the sticky pads on the standoffs securing it in place.
  5. Assembly
    bulletUsing the M4 screws, assemble everything together. The screws pass as follows:
    - Through the BACK of the AntCap
    - through the bottom of the enclosure
    - into the top of the enclosure
    bulletTighten the screws

Link Tests

This NetStumbler file shows two sections:
bulletFirst = Standard BiQuad (no PCB, no enclosure)
bulletSecond = AntCaptenna

The test setup was:

AP 30mW radio connected to a 180-degree waveguide
(See BICTON-AP for details)
Distance 870m
Test End 30mW RoamAboutDS PCMCIA card, 200mm pigtail,
plus antenna under test.

 

Click image to see full scale

Download file

 

Price

See Prices

Site Meter    Copyleft: Rob Clark 2003    Comments?: Webmaster     

FWD Number:
71950

   Recommended Site: