Christmas Dinner

Christmas Dinner at Evan’s Bay Yacht Club has been and gone.  It was a very good Christmas ham meal with special vegetables and salad.  We all enjoyed the great view over the water and the quiet and peaceful setting.  I imagine we may want to return again next year!

All the best of the season to our members.  Don’t forget the BBQ at the Chairman’s home on Wednesday 21 January at 6pm.   Everybody is welcome!   See the contacts section for phone contacts.



Hamnet: A new communication mode for WARC members

ZL1AXG now on Hamnet a Mesh Network for amateur radio operators
ZL1AXG now on Hamnet – a Mesh Network for amateur radio operators

Three WARC members have recently established a Mesh Network (Hamnet) on 2.4Ghz using Ubiquiti Nanonstation M2 equipment and Linksys WRT-54 routers.   These pieces of wifi equipment operate on WiFi channel 1, but because this is in the amateur 2.4Ghz spectrum we are able to load mesh software developed by amateurs and, if necessary, operate on higher power and with gain antennas.  The Nanonstation M2s seem to have good signals over 2Km paths with just 500mW of power, allowing 130Mps traffic.  The Linksys devices have a more limited range and lower speeds.

An IRC chat node, webserver, bulletin board and demonstration video application are up and running!

For further information contact James ZL2ET to get yourself connected as a new node.   Cost is around $170.  You will need a computer!

Temporary installation of Ubiquiti Nanostation M2 equipment running on Hamnet
Temporary installation of Ubiquiti Nanostation M2 equipment running on Hamnet

Fun with Four (Square)!

by Mike ZL1AXG

A four square antenna has now been built and assembled, assisted by a number of local amateurs (Doug ZL2AOV is photographer, Bernard ZL2BD, James ZL2ET, flatmate Josh, and Malcolm ZL2UDF and myself are in assembly mode).

Full testing wasn’t possible because 20m at the test location in Grenada Village was full of local QRN at S6+ and peaking over S9.  It did, however, pull in stations on 15m, even if it was not designed for that band!

The team are busy assembling the portable four square array for 20m.

The array takes about an hour to assemble:  four antennas, four feedlines, a control box, coax and an ethernet line back to the rig and remote control, and 32 radials!

Bernard ZL2BD measuring the impedance at the feedpoint with his antenna analyser. Note that we found in this first test that the initial feed arrangement wasn’t satisfactory, creating too much coupling to ground.  Doug reworked the “feet” giving them nice painted toenails (in British racing green).

I started this project with the intention of engendering interest in phased vertical arrays.  I imagine that the club will get to play with this antenna (and hopefully others like it) in our annual efforts in Oceania DX Contest and CQ WW contests.

20m was picked as a starting band because element lengths are manageable (approx. 5m).  If there is a band where your signal needs to stand out in a contest then it would be 20m!  A four square has around 5.5dB of gain over a monopole, similar to a horizontal beam antenna.   However, all assembly is done on the ground, there is no rotator and it is very quick to switch directions.

What a tiny box!  James ZL2ET and Mike ZL1AXG can be seen pointing at the controller.

You can spot the 1/4 wave current forcing 75 ohm feed-lines from the controller box to each monopole.

The control box and remote unit

The controller is not frequency dependent – containing only switching equipment (3 DPDT relays) and a broadband transformer.

To get the 90 degree offset for the centre radiators you use two pieces of coax, in a Christman matching arrangement. The lengths are calculated using a computer program downloadable from W7EL’s website at  You simply input the impedances of the component monopole antennas measured using an antenna analyser, the configuration of the array, frequency and velocity factor of the coax.  Out pops the lengths of coax to be cut in metres.  The program solves two complex number calculations behind the scenes.  Simple!

The two pieces of 75 ohm coax (one is 2.395m long, the other is 7.799m long) are joined together with a Tee connector creating a common voltage feedpoint where they are fed with 50 ohm coax (grey RG8U) from the rig.  These feeders plug into the controller, giving 0 (rear element) and  90 degrees (centre elements) of phase difference.  The 180 degree shift (front element) is achieved using a broadband transformer constructed on a FET240 type 43 ferrite toroid sourced from SICOM Ltd.

4-square-Christman-method circuit

I am working on constructing a hybrid coupler as well, in order to compare the different feed arrangements.  Hybrid couplers are frequency specific as they contain both inductance and capacitance.   They are popular in commercial units as they are not as sensitive to the antenna feedpoint impedance.  Some say they are more lossy than Christman feed.  We shall see!

A special thanks to Malcolm ZL2UDF who provided the aluminium tubing for the four antennas (ex Quartz Hill 20m beam), Bernard for assistance in calculating the 1/4 wavelength feeder lengths and velocity factor of the 75 ohm coax and supplying the antenna analyser, and Doug ZL2AOV who reworked the “feet” and connection mechanisms for the antennas, and resolved the resonance issue so that they tuned up properly.

At the next club meeting on Wednesday 19 November at 7.30pm, you will hear me talk a bit more about phased vertical arrays in general. I will discuss why these arrays make sense for contesting, basic configurations (2, 3, 4 or more elements), switching and feed arrangements.  I will also cover off practical design ideas for both this portable four square and my as yet unfinished two element multi-band array under construction.

Our October Meeting will be a busy evening

Baluns and antenna tuners with our special Canadian guest, Dave McCarter VE3GSO


Our annual Blackwood Cup shoot out for best home construction project.

Lutheran Church Hall, King St, Mount Cook at 7.30pm on Wednesday 15 October 2014

Supper will be served as always.  Please feel free to join us.