[Elecraft] Franklin antennas

[donovanf at starpower.net]

Hi Paul, 


Here's the answer to question about when the Franklin antenna was invented. 


https://www.aktuellum.com/mobile/circuits/antenna-patent/patents/242342.pdf 


Patent applied for in 1924 before much was known about MF skywave propagation. 


73 
Frank 
W3LPL 

----- Original Message -----

From: "Paul Christensen" <w9ac at arrl.net> 
To: elecraft at mailman.qth.net 
Sent: Wednesday, September 12, 2018 1:50:06 PM 
Subject: [Elecraft] Franklin antennas 

>"Both stations have extensive ground systems that would not be needed if 
they were dipoles." 

AMBC ground systems would still be needed (unless sited over salt water) to 
maximize ground-wave coverage even if they were center-fed vertical dipoles. 
The field intensity produced by a ground-mounted, center-fed 1/2 wave dipole 
is the same as a voltage-fed (at the tower base) vertical radiator. 

The majority of omnidirectional, high-power AM stations use anywhere between 
180 to 195 degree towers, voltage-fed at the base. In essence, they behave 
like vertical dipoles and in each case, they employ extensive radial 
systems. With either feed, maximum RF current occurs at the mid-point, and 
maximum voltage at either end. 

I don't recall if the Franklin was developed before or after studies showed 
that multi-lobe skywave radiation is minimized with 190 degree monopole 
radiators. That's the reason why so many legendary high-power stations use 
a tower height slightly longer than a half-wave while ground field intensity 
is essentially identical to the half-wave radiator. 

Paul, W9AC 
(Ex-RKO Radio, Chicago) 

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