Tuning the Butternut HF6V for 80 m

I am using a Palstar ZM-30 antenna bridge to tune my new Butternut HF6V
vertical antenna. The antenna is ground-mounted, and the ground system
consists of 32 wires with an average length of about 30 feet laid on the top
of clay soil.

I have no problem finding resonance on 80 m, but the impedance at resonance
seems to be low. The adjustment instructions for the HF6V state that
air-wound coil (Q), at the base of the antenna, should be adjusted "for even
lower VSWR" by stretching the coil. Coil (Q) is installed as a shunt at the
feedpoint of the vertical.

I have made all measurements at the antenna, i.e., at the junction of the
coax 75 ohm matching section and the main 52 ohm transmission line. When
coil (Q) is fully compressed, length of about 2.5 in, I measure an impedance
(at resonance) of 20 ohms (SWR?2.5) . When the coil is expanded to a length
of about 4.75 in, I measure an impedance of 25 ohms, corresponding to an SWR
of about 2.0.

The problem is that I have run out of lead length to expand the coil. Should
I leave things where they are now, or should I wind a new coil with about
half the turns and continue with my measurements?

John, N9JG


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