Alan Peake wrote:


Brian Howie wrote:

MMANA gives 3dB degradation for Fe over Al (11ele DK7ZB on 2m), which
surprises me. What does Eznec give ?

Brian GM4DIJ

Using an 11 el DL6WU at 144.2MHz and 10mm elements, EZNEC gives gains of
14.31 dBi for Al and 14.22 for SS. With 5mm elements, it's 14.54 for Al
and 14.37 for SS.
I used a figure of 7e-7 ohm-m for the resistivity. Most stainless steels
range from 5e-7 to 7.4e-7 ohm-m.
3dB does seem excessive.
Alan VK2ADB

Apparently Brian used iron as the model material, which of course is
magnetic. Skin depth is reduced, and therefore RF resistance increased,
by the square root of the permeability. So if the iron model's
permeability is, say, 100, it would increase the effective resistance by
a factor of 10.

Some stainless steels are magnetic, some are not. The magnetic ones have
much higher RF resistance than the non-magnetic ones for the above reason.

Roy Lewallen, W7EL