About quad and metallic spreaders.

When a friend asked:

“Hello I am going to build me a 2-element quad antenna and fiberglass rods for the spreaders are difficult to get, but I have 12mm aluminium tubes.
Can I use aluminium tubes for spreaders (of course with isolators on the end for the wire)?
Does the aluminium tubes do any negative for the transmitting and receiving of the antenna?”

The short answers were:

Yes aluminium tubes interfere with the quad.
You CANNOT do this if you plan to insulate only wire end.
You MAY try if you will be able to effectively insulate at boom end, too.

Below you may read the full story.


So on, we will start with quite a common project for a two-element quad.

The antenna does have a gain of 6.88 dBi and a nice pattern.

Feed impedance is 142 ohms. You may want to feed it via a quarter wave transformer, though isn’t that the question we’re answering to.

What if we add aluminium spreaders to model?

Unluckily two of them, joined together at boom, do have a length in the range of 4 meters. The tube will radiate, and will easily destroy gain and pattern.

We’re not concerned about impedance here, but of course the impedance is affected, too.

For the sake of simplicity I’d not discuss boom connection to mast and mast connection to earth. The above approach is already impracticable, obviously.


But, what if we insulate at boom too, half breaking the spreader? Now the tube is just 1.9 meter in length. It will radiate, but not so much.

Pattern isn't too bad

and impedance will quite compare with the original model.

This may worth a try.

Of course I cannot guarantee about the result, it depends of how effective is the insulation stuff.
As a field test, look at F/B, antenna should have at least some, and look at impedance, must be well over 100 ohms. If those are saved, gain is saved too.

Have fun. Paolo aka 1839.