[TowerTalk] EFHW core

[Richard (Rick) Karlquist]

On 9/29/2020 11:35 AM, Tom Osborne Sr. wrote:
> I put up an EFHW and it worked.
> 
> I just don't know how we ever put up antennas back in 'the day' before
> modeling.  I worked 260 countries with a Gotham quad tribander.  You know -

> Tom W7WHY
> 

When I put up my EFHW 35 years ago, I built an antenna
noise bridge to measure the impedance.  That works
even better than modeling.  It turns out that it is
difficult to model the high drive impedance.  I
modified the bridge to center it at 1,000 ohms instead
of 50 ohms, and replaced the air variable cap with varactors,
and replaced the pot with PIN diodes.  This allowed
me to install it at the top of the 50 foot
tower, but operate it remotely from the ground.  Worked perfectly.
When I put the resulting matching network at the top
of the tower, it worked exactly as predicted by the noise
bridge.

Rick N6RK