Jeffdeham wrote:

I was looking at the rainbow tuner which matches a
half wave end fed antenna to 50 ohms using a quarter
wave radial. I am guessing it
works like a transformer but not sure. Here is
the schematic;

Ant |----- quarter wave radial
| |
| GND
----------
| )
--- )
Variable )----- 50 ohm
--- )
| )
| )
----------
|
GND


If it does work like a transformer how does it do it?
How is the matching done?

Thanks for any help!

Jeff

The fed end of a half wave antenna appears as a high impedance.
The parallel resonant circuit (at resonance) also appears as a high impedance.
To match the low impedance of the feedline, it is necessary to
tap down on the coil (so as to feed between the tap and ground) -- like
an autotransformer.

Think of a half wave dipole -- you need good insulators on the end
of the half wave because the voltage there is very high, and the
current is very low. Uzing (pardon the pun) Z=E/I=High/Low yields
a high impedance.

This is a pretty simplified explanation, but if you think about
it it will work.

Hope it helps you to understand things a bit.

Irv VE6BP
--
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