[BC] Franklin

[Cowboy]

On Wednesday 20 July 2005 16:15, Barry Mishkind wrote:
> At 01:07 PM 7/20/2005, Cowboy wrote
> >On Wednesday 20 July 2005 15:49, Neal Newman wrote:
> > >  Very Cool so Basically a Franklin is a Vertical  center fed Dipole. I
> > > would assume with it Being such
> > > there is No Ground Radial system?

> >  As such, it does require a standard ground system.
> 
>          I will defer to your knowledge on this one,
>          however, my musty memory (it gets musty
>          very fast these days <g>) recalls being told
>          there was none, or very little at one point.

 That could be true, but in my book would be wrong.

On Wednesday 20 July 2005 16:43, Paul Christensen wrote:
> > It's 180 over 180 and both sections are fed IN phase.
> > That's where the gain comes from.
> > ( a coaxial colinear, such as a Phelps-Dodge StationMaster is the same 
> > principal )
> > A dipole has the two sides out of phase.

 addendum...
 though the current in a dipole is all flowing in the same direction.
 The two halves are out of phase with respect to the center feed.

> It appears the current distribution of the Franklin is such that current 
> maximum appears at 90 and 270-degrees above the ground. 

 Unless is tuned for beam tilt......
 ( think two bay FM )
 ;-)

> If that is the  
> case, the ground system would function just as it does with a half-wave or 
> 190-degree radiator -- meaning that it is still necessary, but is 
> considerably less ground-dependant than a radiator of less than 180 degrees 
> in height where radiation resistance becomes increasingly dependent on the 
> quality of the ground system beneath it.

 True, but......

 Depends on what's meant by "ground system".
 As Clive points out in another thread, ground is not "ground" as regards
 a radiator.
 Some say it's a mirror of sorts, and performs as if placing a candle on a mirror.
 That's true, to an extent.
 Some say it's much the same as taking the missing lower half of the antenna,
 and spalying it out into 120 sections, and laying them on the ground, instead
 of burying half a tower.
 That's also true, to an extent.
 Some say it's a shield, isolating what's below from what's above.
 That's true, to an extent.
 Some say that it's a capacitor plate, so that the antenna has a surface
 to capacitate against.
 That's true, to an extent.
 Some say that the dirt ( whether it's ground or not ) acts as a resistor, and
 dissipates the power as heat, and the "ground system" is to decrease the loss
 in the resistive dirt.
 That's true, to a great extent, and has the most pronounced effect where the
 current density is highest, close to and right at the antenna location.

 It's this last reason that is why ANY ground mounted antenna should have
 as much of a "ground system" under it as possible.
 The power density at the base of a Franklin may not be too high compared
 to other configurations, but the ground losses nearest the radiator are where
 we have the most control, and where the losses will be highest, so it too,
 should be worked against as much of a ground system as possible.