That's much, much more difference than can be explained by the different
conductivities of the metals. Either some very resistive alloys are
involved, or there are differences between the antennas other than the
type of metal.

Roy Lewallen, W7EL

H. Adam Stevens, NQ5H wrote:
One place where I can clearly see the difference between copper and aluminum
is comparing my (copper) Nott screwdriver with my (aluminum) Tarheel
screwdriver or my (aluminum) Hi-Q mobile antenna on 20 meters.
Mounted on my Durango, at resonance the Nott's impedance is 9 ohms, while
the Tarheel is 20 ohms and the (smaller tube) Hi-Q is 30 ohms; Measured with
the same whip in all cases.
This is a case of a short antenna.
The difference is significant and easily measured.
73
H.
NQ5H