Re: Franklin antennas

Posted by donovanf on Sep 12, 2018; 7:14pm
URL: http://elecraft.85.s1.nabble.com/Franklin-antennas-tp7644985p7644989.html

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" <[hidden email]>
To: [hidden email]
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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