LinkBack Thread Tools Search this Thread Display Modes
Prev Previous Post   Next Post Next
  #10   Report Post  
Old November 29th 05, 10:43 PM posted to rec.radio.amateur.antenna
Richard Harrison
 
Posts: n/a
Default Antenna reception theory

Reg, G4FGQ wrote:
"It is impossible for an E-field to exist without an H-field."

Agreed.

By definition an electromagnetic wave includes an electric component and
a magnetic component. That does not mean the components are inseparable.

The purpose of a Faraday screen is to eliminate capacitive coupling
while permitting magnetic coupling.

I`ve worked in several medium wave broadcast plants. In these, each
tower was coupled through a 1:1 air-core transformer to its transmission
line. The transformer consisted of two identical coils, one on either
side of a Faraday screen. The coils shared a cmmon axis.

Electrically, the transformer was transparent at the transmitting
frequency. It coupled the transmitting frequency as if the transformer
did not exist to impede. Its purpose was to eliminate capacitive
coupling, The Faraday screen provided a place where electric field lines
are shunted to ground.
The problem with capacitive coupling between a transmitter and a tower
is that the higher the frequency, the less the reactance or opposition.
The coupling is better through a capacitance to the harmonics of a
frequency than it is for the fundamental. The Faraday screen removes
this unwanted bias for imroved harmonic propagation.

A side effect of the Faraday screen is that it removes lightning strokes
before they reach the transmission line from the tower.

The Faraday screen looks like a metal rake. Its back where the teeth or
tines join is firmly grounded. The teeth are open-circuited. Current
cannot circulate between and through the teeth, so no counter
electromotive force can be generated to oppose magnetic coupling between
primary and secondary coils. The rake is transparent for magnetic
coupling but it is a stopper for electric coupling.

By complete shielding, that is metalllically enclosihng one or both
coils of an impedance coupling pair, magneric coupling between them can
be practically eliminated. A coupling capacitor between the coils allows
only the electric field to be effective. There`s no magnetic field
involved.

I`m no advocate of the E-H antenna, but the electric and magnetic
components of a wave are easily separated.

Best regards, Richard Harrison, KB5WZI



 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Inverted ground plane antenna: compared with normal GP and low dipole. Serge Stroobandt, ON4BAA Antenna 8 February 24th 11 11:22 PM
significance of feedline orientation Brian Shortwave 6 October 22nd 04 02:43 AM
Question for better antenna mavens than I Tony Meloche Shortwave 7 October 28th 03 10:16 AM
QST Article: An Easy to Build, Dual-Band Collinear Antenna Serge Stroobandt, ON4BAA Antenna 12 October 16th 03 08:44 PM
Outdoor Scanner antenna and eventually a reference to SW reception Soliloquy Shortwave 2 September 29th 03 05:04 PM


All times are GMT +1. The time now is 07:30 PM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017