LinkBack Thread Tools Search this Thread Display Modes
Prev Previous Post   Next Post Next
  #4   Report Post  
Old April 6th 04, 08:28 PM
Richard Harrison
 
Posts: n/a
Default

Dan Jacobson wrote:
"I will put my wire to work to pull it in even better."

Fitst, you need a line-of-sight path to the desired station. Then, you
need an obstruction in the response to unwanted signals. You need enough
desired signal edge to capture the FM detector and to suppress noise the
undesired signals might add to the mix.

An axial mode helical antenna uses a lot of wire wound into a coil which
is pointed at the desired station, directly or indirectly. Diameter and
coil pitch are optimized for axial gain and directivity.

If a helical coil is small in terms of wavelength, its field is maximum
perpendicular to the coil axis. Such a self-resonant coil makes an
omnidirectional antenna in a plane perpendicular to the coil axis.

We have a rubber ducky as an example of an omnidirectional helix which
is inefficient, limited in bandwidth, but convenient for handie-talkies.
Larger omnidirectional (normal-mode) helices are used by some VHF/UHF
broadcasters to provide circular polarization, but Kraus says on page
173 of his 1950 edition of "Antennas":

"For normal mode the dimensions of the helix must be small compared to
the wavelength, so that from band width and efficiency considerations
this mode is not readily applicable in practice."

There are handie-talkie suppliers and broadcasters who don`t heed Kraus.

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
Excessive RF Exposure from Long Wire? jj Antenna 22 February 13th 04 10:32 PM
randon wire newbie question lethal Antenna 4 February 7th 04 11:01 AM
Open Wire Feeder Switching Ideas ? DOUGLAS SNOWDEN Antenna 4 December 30th 03 07:37 PM
Lightning protection for remotely tuned wire antenna Minnie Bannister Antenna 0 December 27th 03 05:31 PM
Feedpoint impedence / wire diameter Tom Bruhns Antenna 0 July 10th 03 08:23 PM


All times are GMT +1. The time now is 10:54 AM.

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