[BC] Franklin MW Antenna Ground Unneeded?

[Richard Fry]

For discussion...?

There is a belief that Franklin antennas do not need/use conventional, 
buried radials for an r-f ground.  Possibly that might related to thinking 
that, as a 180/180 Franklin is fed across an insulator 1/2 way up the 
structure, it must operate similar to a center-fed dipole -- and a dipole is 
a balanced radiator not needing/using an r-f ground to produce its gain and 
pattern.

A NEC2D study was done to compare the result of mounting a center-fed, 
full-wave vertical dipole cut for 1530 kHz with the lower tip of its lower 
arm 1.5 meters above a perfect earth with the same dipole in free space 
(link below).

The vertical plane pattern from that dipole near the earth is not the best 
as far as nighttime self-interference is concerned, and doesn't match the 
pattern produced by a true Franklin.

The two sections of a Franklin are not "driven against each other" as in a 
true dipole. The current and phase distribution along the two sections of a 
Franklin are not the same as along the arms of a center-fed dipole of the 
same overall length.

I'm thinking that in effect, the two sections of a Franklin are both 
monopoles, and need to be driven against a low-loss connection to the r-f 
ground plane for the same reason that a conventional, base-driven, series 
fed, vertical monopole needs to be.

http://i62.photobucket.com/albums/h85/rfry-100/V_Dipoles_Compared.gif

RF