LinkBack Thread Tools Search this Thread Display Modes
Prev Previous Post   Next Post Next
  #11   Report Post  
Old November 22nd 14, 10:09 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 409
Default Interesting bent folded unipole antenna



"John S" wrote in message ...

On 11/22/2014 10:19 AM, John S wrote:
A special purpose antenna for maybe just below the 6M band. For railroad
cars (a large metal ground plane). The antenna must be short enough to
pass through tunnels and have a 50 ohm feed impedance.

I saw this antenna in a book but I can no longer remember which book
and, although I've searched, I can't seem to find a reference. It was
probably from the 1950's. Anyway...

Imagine a folded unipole over a large sheet of metal. It will probably
have a high feed resistance of 100 or so ohms. But, if it is bent over
90 degrees starting a short distance above the ground plane, it can be
adjusted to match a 50 ohm feed and with no imaginary component. This
will satisfy not only the feed impedance but also the short height
requirement.

Other than the really nice ground plane of a railroad car's roof and
using a frequency proportional to the plane, there is no obvious reason
this cannot be use in other situations.

Is that not really cool? Comments welcome, of course.


# No, Guys, nothing that I have read so far is the thing I have in mind.

# Picture this...

# A folded unipole on a large sheet of conductive material. Let one of the
# vertical elements be connected to the sheet. The other is insulated from
# the sheet and has the generator attached.

# Now, this configuration has a high feed impedance, even when resonant.
# However, if you now bend the antenna at an appropriate point vertically
# so that the top portion leans horizontally to the sheet, the antenna
# gets lower to the sheet and the impedance lowers.

# I have an EZNEC file that I can share if anyone is interested. I will
# also continue to search my books for the example.

Ahhh....the "folded" part didn't sink in when I responded.

I suspect my original comments still apply.
With two conductors, the current is half in each conductor, thus a doubling
of radiation resistance at the feed point in one conductor.
So by carefully selecting the height at which the vertical part is bent,
there might be a good match for coax.

I'll play with that configuration a bit on EZNEC.

 
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
Folded Dipole Antenna frankieNrosie Antenna 30 December 14th 10 08:25 PM
3-Sided "Bent" Random Wire Antenna Over a Backyard Fence RHF Shortwave 1 August 30th 07 03:21 PM
For Shortwave Listeners (SWLs) : Which is Better to Use ? a FM Folded Dipole Antenna ? -or- a Whip Antenna ? RHF Shortwave 0 July 28th 07 08:26 AM
Antenna Simulation Parameters and Folded Dipole Antenna Question... RHF Antenna 3 January 23rd 07 03:43 PM
NASA Bent Wire Antenna [email protected] Shortwave 0 March 20th 05 07:20 PM


All times are GMT +1. The time now is 10:34 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