Re: LF: David Gibson on Earth antennas and propagation below 9 kHz

[Andy Talbot <andy.g4jnt@googlemail.com>]

I was thinking about this, and thoughts turned to a rather simpler antenna;  the folded dipole and how it would behave when electrically short.

 

A simple non-folded  electrically short dipole (negelecting all losses)  has Rin proportional to 1/L^2 and a highly capacitive reactive term

 

A folded half-wave dipole fed conventionally has Rin about 4* that of a normal dipole due to current sharing in the legs -.

 

Now the conumdrum - what does an electrically short folded dipole look like?     It has got to be inductive, since we're feeding into a squashed shorted turn, and presumably the current distribution looks short dipole-ish.

 

So is it a loop, is it a dipole, is it both, how can it be both, if it is what's its radiation pattern ?

Similar to the ground loop/dipole question ?

 

And is there a length where the inductance of the loop bit resonates with the capacitance that 'ought' to be there due to its also being a short dipole.

 

?????????????????????????????????????

 

Andy
www.g4jnt.com

(not really an antenna sort of person)

On 21 July 2010 08:12, John Rabson <john.rabson@numeo.fr> wrote:

Reposted by permission

John F5VLF

The antenna is a "horizontal end-grounded line current" antenna; commonly referred to as a "horizontal end-grounded electric dipole".  The word "dipole" is often used a bit too loosely, although that is a moot point. If you think "horizontal electric dipole" you get the general idea: its an electric dipole, not a loop antenna.