THE G4ZU….SPIDER BEAM……SKYPPER
This 3 elements wire Yagi comes along in a great variety of names. On the 11 meter we call it the Skypper due to the manufacturer Alex 1SD019
On Ham bands we call it the Spider beam or G4ZU.
What ever the name is its principle remains the same. It is a full-size 3 elements Yagi with the Director and Reflector bend towards the radiating element.
With this comes a small size Yagi with Gain 7,3 dBI and Front to Back in the order of 30 dB
It is easy to build, with the materials in front of me I had the first SWR test within an hour. And provided a great match within the 700 Khz bandwidth.
This is one antenna i will not get ride of…always handy for DX-expedition, Holiday or Back-up for home
The materials you need:
4 X fiberglass poles
Teflon wire about 5 meters
Electrical wire 15 meter
2 X U bolt
1 meter aluminum tube (80cm)
small aluminum plate about 5 centimeters long 2 centimeters wide
The fiberglass poles :
I used are fishermen tubes, each of a length of 4 meter lengths. You will need only about 2,5 meter of the fishing rod but the lower part of it is stronger therefore the antenna will stand through have wind. It is easy possible to make the framework from other materials, I have seen models made from bamboo as well.
The Teflon wire :
used, originally wash line Teflon…4 mm, but any NON-guiding wire is usable (perhaps from sailing boats that’s extra strong)
The Electrical wire:
Any plain black and red 12 volt wire, or other form of electric guiding wire is good..(example: loud speaker wire )
The U bolts we find on any old 27 mhz antenna are fine. You can also buy them at the local hardware store. Just make sure it fits the mast the beam is supposed to go on.
The 1 meter aluminum tube has either fit INTO or AROUND the fiberglass poles in such a way that there is not to much friction.
Cut the aluminum tube in 2 pieces of 50 centimeter or 40 centimeter…no that critical.
– drill 2 holes close to the center of each tube. The sizes need to be large enough for the U-bolts ( see picture below)
MAKING OF THE FRAMEWORK:
The first thing you should do now is put the U bolts though the aluminum tubes and connect the aluminum tubes to a mast. Make sure you have about 30 centimeter of mast left above these aluminum tubes.
Connect the tubes above each other with 90 degrees difference. as shown in the picture
Connect the 4 fishing rods to each open end of the aluminum tube. Now looked from above you should see a cross.
MAKING OF THE ELEMENTS.:
Cut the electrical wires in pieces of : 5,25 meters (the reflector)
5,04 meters (the radiator)
4,84 meters (the director)
Take the reflector and put in the center of the reflector a little tape. This will help you determine the center of the reflector later.
The same counts for the director.
Take the radiator and cut it in half. You now have two pieces of 2,52 meter. uncover the sealing from both wires at one side for about half a centimeter.
Solder the uncovered electrical wires. Each independent. And enter them in the block-connector. This is your access for the coax. There are many more ways to attach the coax cable on it but this is about the simplest way.
What I did was take a small aluminum plate drill holes through it and used that for braking the tension.
PUTTING IT TOGETHER:
Attach the radiator on the mast about 30 centimeters above the aluminum cross.
Connect the Teflon wire (about 2x 50 centimeter) to the radiating dipole at both ends the knobs you can use for that are as follows:
This knob will tighten itself when tension is brought on it.
Attach the Teflon wires to the fishing rods they should be in a bowl position now.
Attach the other fishing rods…
Bend the fishing rods upwards and measure 2,5 meters from the Block-Connector. Put a tape around both fishing rods at that point. (this will be approx 2,6 meter)
Connect the Reflector (tape on tape) on a fishing rod. And connect the Director on a fishing rod. (again tape to tape)
You could connect them with either wire or T-reps.
Bring the Teflon wires towards the fishing rod. of the radiator and attach them at the same point where u attached the radiator.
Make some final small adjustments that a nice square is produced.
For long lasting results you could improve the coax connection, get rid of the T-reps. and a paint on those fishing rods would not be misplaced.
The cost I made for this project was in the order of 40 euro’s I believe this could have been around 25…30 euro’s simply because I bought fishing rods that were 4 meters long but 3 meters can do the trick as well.
For the first time building you will probably need about 3..4 hrs to make everything right, that’s not bad for an antenna that will work as good as any 3 elements yagi!