Topband: shunt fed tower

DM4iM hamradio at
Sat Jan 22 14:42:10 PST 2011

thanks to all who responded.
Special thanks to Greg, ZL3iX, for the pictures.

I connected the parasitic elements per his hints
and the SO-239 plug at the radiator housing to the boom.
There is a balun inside the housing, so grounding the plug also grounds 
the radiator via the balun.
I know from building VHF-Yagis that there IS a difference in distance 
and lengths for the elements when they are connected to the boom or 
If there is any ill effect to the SteppIR, i can easily remove these 
connections, but so far i don't notice any down side. I had a number of 
replies from topbanders using their SteppIR for a tophat even QRO+.

At 1820khz now R=28.6 and jX-3.6 with the SteppIR in the 14Mhz position.
This results in an SWR=1.76.
R drops to 26.9 and jX to -18.2 when the elements are home.

Now, what do the numbers tell the gurus? Input welcome.


Tower 17m, 5m mast above trust bearing, 6m-yagi on top
shunt-wire abt 1m from tower, attached highest possible
SteppIR above trust bearing, all elements grounded.
12 short Radials on ground.
gamma match

I think this is a good starting point for improving the antenna.

Begin with radials?


Martin DM4iM

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