Buck wrote:

How is the "tuner extender" made? is it simple enough to duplicate
with a home-brew?


A tuner extender is about worthless. It is an autotransformer. Nearly
every auto tuner has more impedance range than the ferrite core
autotransformer used to extend the tuner.

The problem really is the Cobra does NOT have resonances at the points
that are claimed, so impedance is off the scales on some Ham bands.

I measured a Cobra that was supposed to hit 80, and it missed by a few
MHz. A person would be much better off doing something else, although
I'm sure with a good tuner contacts could be made on any band.

After all.... I can work Europe on 160 SSB and VK's on CW with my
mobile antenna, and it is less than 1% efficient and that is on 160!!

73 Tom