You can make an aluminum core PEX loop antenna easily. This material is cheap, lightweight and easy to form a permanent loop shape. But hard to find!
Previously, I have written about different materials for making small magnetic loop antennas. These included wire, copper and aluminum tubes, and metal foil. For my wideband loop project, I decided to try something different.
A few hobbyists have written about making PEX-AL-PEX, or aluminum core PEX loop antennas. Say, what? I must admit that until recently, I had never heard of the stuff.
PEX is cross-linked polyethylene, a very strong plastic. You will find PEX used extensively for domestic water piping, as well as hydronic radiant heating and cooling. Some versions of PEX come with an aluminum core and are used mainly for heating. PEX-AL-PEX is basically two layers of PEX with a thin layer of welded aluminum sandwiched in the middle.
So, I bought some half-inch aluminum core PEX loop material. The dimensions are 0.5″ inner diameter and 0.64″ outer. From my measurements, I estimate the aluminum core is about 0.04″ or 4 mm thick, with a radius of around 14.5 mm.
Is this aluminum thick enough for use as an antenna. Yes. Skin depth of a radio signal at 1 MHz is 0.08 mm. When a radio signal travels through a conductor, most of it stays within five skin depths from the surface, so 4 mm thickness is more than enough.
Aluminum Core PEX Loop Material Sourcing and Use
Hard to find, easy to use. I searched for a supplier of aluminum core PEX loop material in Alberta. The one I found would not sell me a small quantity. Fortunately, I came across HEAT Innovations in Winkler, Manitoba. Sales manager Mike was happy to sell me a fifty foot roll at a good price and ship it to Calgary.
PEX-AL-PEX is very lightweight and easy to form into a 1 meter diameter circular loop. On top of that, I found that it holds the shape well.
To make a mechanical or electric connection to the aluminum, you need to remove some of the PEX outer or inner layer. Given the low melting point of polyethylene compared to aluminum, I just used an old soldering iron to melt away some of the PEX, as shown in the picture above.
One last note. You need to paint the PEX for ultraviolet protection before it goes outside.