Re: [TowerTalk] Fwd: OCFD

[Patrick Greenlee <patrick_g@windstream.net>]

Most of our antennas (those of us not going to the ISS) are not in a 
vacuum so the velocity factor of our antenna components is not what it 
would be if they were  A N D   the active portions of our antennas 
aren't an infinite distance from everything in the universe (especially 
conductors) resulting in yet another deviation from the theoretical. In 
recent decades rain water is not even close to simple distilled water 
but is more typically a weak acid that is a conductor.  Typical antenna 
insulators with lots of fins to increase path length for leakage 
currents haven't changed much in the last several decades and have  N O 
T  kept pace with the increased conductivity of rain water.
Patrick        NJ5G


On 3/26/2017 12:17 PM, Hans Hammarquist via TowerTalk wrote:
> Hi Jim,
>   
> Everything has a capacitance to somewhere. Even Mother Earth has a
> capacitance. You can select what reference point you like, Moon, Sun, Pluto. I
> never really grasped it myself when I took my classes in physics.
>   
> Anyhow, there is a distributed capacitance along the dipole wires that get,
>   what's called, end-effect. That's why you don't cut the dipole to exactly
> 1/2  wave length but a little shorter, most around 95%.
>   
> We all, I hope, know that the voltage is highest at the tips of the dipole
> (or 1/4 wave verticals for that matter). That's why you put a good
> insulator at  the dipole ends, not just a non-conducting cord (what might catch 
> fire
> a rainy  day).
>   
> Just my dime to the conversation,
>   
> Hans - N2JFS
>   
>    
> ____________________________________
>   
>
> ## BTW,  when you mentioned dipoles etc, having all their voltage at the
> tips,as
> a  result of capacitance,  capacitance between what and what ?    Is it
> capacitance
> between the tips, like in an arc ?    I cant  see it being C to ground
> below.  What
> if the dipole is in outer space  ?
>
> Jim   VE7RF
>
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