[TowerTalk] Fwd: OCFD
Patrick Greenlee
patrick_g at windstream.net
Sun Mar 26 13:44:43 EDT 2017
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
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
More information about the TowerTalk
mailing list