[TowerTalk] Choking on chokes

[Jim Brown]

On Wed,12/3/2014 3:31 PM, Roger (K8RI) on TT wrote:
> Take for instance the 75 meter, center fed dipole whose impedance can 
> vary widely from well below 50 ohms to above 50 ohms depending on 
> height.   You are feeding a supposedly balanced antenna with 
> unbalanced line.  (Good place for a choke). 

And it also varies widely from one end of the band to the other. We can 
see this on a Smith Chart and on an SWR curve beginning around slide 
#30. This particular dipole is modeled around 100 ft over average 
ground, and Z at resonance is 76.5 ohms. Over lousy ground, the Z would 
be in the mid- to high-80s of ohms.

http://k9yc.com/PacificonSmithChart.pdf

73, Jim K9YC