Topband: End Fed Twin Lead Marconi Antenna

Steve Flood kk7uv at bresnan.net
Tue Mar 4 19:12:36 EST 2008


----- Original Message ----- 
From: "Jim Brown" >
> Or, even better, simply make the horizontal section longer until the
> feedpoint is 50 + jxxx ohms, and add a capacitor in series at the base to
> tune out the jxxx ohms. I'm doing that here, and it works well. The 
> vertical
> is about 86 ft, the horizontal is about 70 ft, and the cap is 350 pF. This
> centers it at 1825 kHz. These values will vary a bit depending on your
> terrain (mine slopes) and the resistance in your radial system.


I have a similar antenna.  Mine is about 75 foot vertical wire with a 75 
foot topwire, over a field of 60 radials that vary from 50 feet to 130 feet 
on a steep slope.  My feedpoint Z measured 25 + j0 at 1825 kHz.  I added a 
2:1 UNUN at the feedpoint to get 50 ohms.   Is the UNUN approach better or 
worse or about the same as the reactive antenna with series capacitor 
approach?   I ask because I'm going to take the antenna down this summer to 
replace the wire and insulators (they've taken a beating from the wind and 
swaying tree supports) and upgrade everything for high power.

Steve, KK7UV 



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