"albedo" wrote in message
...
HI

Does anyone could tell me what is it inside the "matching assembly" of the
Cushcraft R3 antenna ?
I suspect two circuits in serial resonance ?
Am I right ?

Thanks

Dan

Prentice - N4VBH asked this identical question on rec.radio.amateur
equipment on May 31, 2007

Manual is on BAMA
http://bama.edebris.com/manuals/cushcraft/r3

Photo of the Cushcraft R3 capacitor, motor (used for a N0HC loop design)
http://www.geocities.com/n0hc/loop

According to the notes of Joe, W1JR (who has one of the largest Cushcraft
manual collections), the Lower capacitor, the one closest to ground is
around 78 pF and
the Upper capacitor is around 138 pF.
I'm sure anything near that value will be sufficient.

Actually the ancestor of the R3 and R7 verticals was the "Ringo" series,
which is an end-fed half wave radiator. They were made for 10m and up. The
parallel-tuned circuit at the feedpoint uses a single-turn tapped coil and
the capacitance between the end of the antenna element and the mounting
tube. The R3 extended this to multiple bands by using a trapped antenna
element (still electrically a half wavelength on each band) and a motorized
tuning capacitor for the parallel-tuned circuit.
Newer designs use 'counterpoise' elements below the feedpoint to lower the
feedpoint impedance to a few hundred ohms, but still work on the half wave
resonance principle, and don't
need radials.
--WB6BYU