Copper tube or aluminum tube ?
pa0nhc 20181105 / 20200612.
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The losses of an aluminum radiator can be 4db worse compared to a copper radiator of the same thickness. Stainless steel is even worse.

        After calculations using loopcalc.exe :

For the same efficiency, an aluminum radiator should have 2.5x more thickness
than an equivalent copper radiator has.

= Costs for copper and aluminum tubes differ therefore little.
= Copper and aluminum must both be painted, as bare aluminum oxidizes too.
_ Bending aluminum tube into a circle is a specialists task and very expensive.
_ The welding of aluminum causes :
        extra transport costs of the completed loop to the antenna site,
        impossible moving through housing.
+ Brass knees + tin solder, cost less than the argon welding of aluminum.
+ Copper tubing can be cheaply soldered yourselves for free, using tin solder,
on the definitive antenna site itself.
+ Separate 2.5m long copper tubes can be costless transported in you (small) car, 
and easily moved through buildings.
+ The thinner copper tubing is less obvious than bigger aluminum tubing.

Construction with copper is much easier, and extra costs are much lower.
Think about thick Cellflex coax.