Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old December 19th 03, 10:34 PM
larry d clark
 
Posts: n/a
Default fat conductor question

hi

i've got a question about how wires to use when making
a fat conductor hf dipole(cage antenna)using wire equally
spaced around a circular form. ie target diameter is 8
inches, how many wires around the form, 4, 6, 8?

tnx

larry
kd5foy



  #2   Report Post  
Old December 20th 03, 12:53 AM
w4jle
 
Posts: n/a
Default

While you will probably get any number of answers, I personally have always
used 6. The best supports I have found are slices of 12" white plastic sewer
pipe. You normally can get a scrap piece at your local utility company.

Make them 3/8" thick and put a hole every 60 degrees.

If you want to take a look at the effect of increasing wires or diameter,
Reg has a program for cage dipoles that lets you determine the best setup
for what your trying to accomplish.

Anecdotally, the cages are quieter (less electrical noise) than standard
dipoles. Don't make this statement on here however, because 9 folks will
jump out of the woodwork to tell you how wrong you are.

Good Luck!
"larry d clark" wrote in message
. com...
hi

i've got a question about how wires to use when making
a fat conductor hf dipole(cage antenna)using wire equally
spaced around a circular form. ie target diameter is 8
inches, how many wires around the form, 4, 6, 8?

tnx

larry
kd5foy




  #3   Report Post  
Old December 20th 03, 03:54 AM
Reg Edwards
 
Posts: n/a
Default

Anecdotally, the cages are quieter (less electrical noise) than standard
dipoles. Don't make this statement on here however, because 9 folks will
jump out of the woodwork to tell you how wrong you are.

=================================

What few anecdotes I have read fail to say whether the noise is locally
generated or is the more distant stuff which comes in with the wanted
signals.


There is no possible reason why a fat wire will discriminate better between
between signals and distant noise than a thin wire. To any antenna
everything is just e.m waves. Receiving and radiating patterns, radiation
resistance and efficiency are identical for both.


But local noise sources are within the near field of the antenna. Or the the
antenna can be considered to be within the near fields of a lot of noise
sources.


One end of the antenna can be nearer to some noise source(s) than the other
end. So although the dipole may be accurately balanced relative to ground
(almost certainly it isn't) it may be very unbalanced relative to the
location of local nise sources.

The much greater capacitance of a fat antenna to ground, and to everything
else, will shift the local receiving pattern. The fat antenna will also
have a smaller capacitative reactance to ground and to everything else.
Remember local noise is mainly due to its electric field and so the fat
antenna, all other things remaining unchanged, will have a greater tendency
to decouple itself from local electric noise fields.

The effect is not un-related to screened receiving loops. It will be more
noticeable with decreasing frequency and with decreasing antenna sizes. It
will not be noticeable at all at low noise receiving sites where the
near-fields of the antenna and noise sources do not inter-react.
----
Reg, G4FGQ







  #4   Report Post  
Old December 20th 03, 07:06 PM
Richard Clark
 
Posts: n/a
Default

On Fri, 19 Dec 2003 22:34:39 GMT, "larry d clark"
wrote:

hi

i've got a question about how wires to use when making
a fat conductor hf dipole(cage antenna)using wire equally
spaced around a circular form. ie target diameter is 8
inches, how many wires around the form, 4, 6, 8?

tnx

larry
kd5foy


Hi Larry,

An example design for one configuration may be found at:
http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm

As to your question about diameter and count of skirt wires, review:
http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm
which, although relates to a discone, it serves to illustrate how the
"thickness" comes to bear on bandwidth.

Much of my other analysis simply suggests the more wires, the closer
approximation to the solid cylinder you are trying to build a skeleton
of. The question of how many is good enough should be evident that 16
certainly offers a good approximation, fewer, as revealed in my other
work brings a corresponding poorer approximation.

I've built physical models with up to 6 skirt wires, and although
useful, they did show resonances where the two links above reveal wide
banded behavior. One design was a 40M Discone, another a wideband
vertical dipole (hoping for 20-10M but probably closer to 15-10M).

73's
Richard Clark, KB7QHC
  #5   Report Post  
Old December 22nd 03, 07:37 PM
Tarmo Tammaru
 
Posts: n/a
Default


"larry d clark" wrote in message
. com...
hi

i've got a question about how wires to use when making
a fat conductor hf dipole(cage antenna)using wire equally
spaced around a circular form. ie target diameter is 8
inches, how many wires around the form, 4, 6, 8?

tnx

larry
kd5foy

Larry,

If all you are trying to do is to increase the bandwidth, there are better
ways. For instance, have two dipoles, connected together at the feedpoint,
but with the ends separated either vertically or horizontally. Cut the two
dipoles for slightly different frequencies. I ran EZNEC on such an antenna
for 75/80, and easily got an SWR of less than 2:1 from 3.5 -4.0. You could
mount the support antenna as a dipole, and the other as an inverted V.

Tam/WB2TT




  #6   Report Post  
Old December 22nd 03, 08:56 PM
sideband
 
Posts: n/a
Default

Why not use Romex, connect all three conductors together at the
feedpoint, and cut each conductor for whatever resonant frequency on
each band.. I've done this, and with a little matching it worked out
nicely.

73 de AI8W, Chris

Tarmo Tammaru wrote:

"larry d clark" wrote in message
. com...

hi

i've got a question about how wires to use when making
a fat conductor hf dipole(cage antenna)using wire equally
spaced around a circular form. ie target diameter is 8
inches, how many wires around the form, 4, 6, 8?

tnx

larry
kd5foy


Larry,

If all you are trying to do is to increase the bandwidth, there are better
ways. For instance, have two dipoles, connected together at the feedpoint,
but with the ends separated either vertically or horizontally. Cut the two
dipoles for slightly different frequencies. I ran EZNEC on such an antenna
for 75/80, and easily got an SWR of less than 2:1 from 3.5 -4.0. You could
mount the support antenna as a dipole, and the other as an inverted V.

Tam/WB2TT



  #7   Report Post  
Old December 23rd 03, 12:36 PM
larry d clark
 
Posts: n/a
Default


Many tnx for the excellent suggests!!!
it is much appreciated

larry
kd5foy

"larry d clark" wrote in message
. com...
hi

i've got a question about how wires to use when making
a fat conductor hf dipole(cage antenna)using wire equally
spaced around a circular form. ie target diameter is 8
inches, how many wires around the form, 4, 6, 8?

tnx

larry
kd5foy






Reply
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



All times are GMT +1. The time now is 07:04 PM.

Powered by vBulletin® Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2004-2018 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017