[Elecraft] half wave vertical

[Christopher L. Cowan]

I recently erected a half wave vertical after being inspired by an article "An uncommonly good vertical"  by Ted Hart W5QJR which is in the archives at www.antennex.com.  I was suprised to find that feeding a half wave vertical at the lower end required an impedance matching network 50 ohm to about 3000 ohm but this is an significant advantage.  

Since ground resistance is in series with the radiation resistance of the antenna a higer Z antenna makes the ground resistance loss less significant.  His example: 1/2 wave vertical Z (end fed)=3300ohm. With a ground rod and a few radials ground resistance about 100 ohm.  Efficiency about (3300/(3300+100) =97%.  For a 1/4 wave vertical Z (end fed)=32 ohm and with the same ground, efficiency is 32/(32+100) = 24%!!

Cutting and tuning the half wave element was tricky since it is hard to couple to a 50 ohm driver. I tied the wire end to ground and looped a portion around a grid dip osc coil.   

I followed his suggestion and used a tapped parallel tuned circuit at the base for matching to 50 ohm coax.  Ground is a wire fence with a copper ground rod in clay soil. SWR 1:1 and it works very well.

Chris Cowan KA0A/7 

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