Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: V shaped horizontal dipole  (Read 6449 times)
Guest

« on: February 16, 2002, 12:48:58 PM »

How much effect does slanting the ends of a horizontal dipole forward on the same plane have? Does it favor the direction of slant and how far can the slant go without effecting the SWR much? I realize that at the back end there  would be a loss, but is the added gain in one direction worth the bother over the conventional horizontal dipole?     Bill    
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #1 on: February 16, 2002, 05:12:08 PM »

Hi Bill: Without more details, a general answer is about all I can do. First, most of the radiation from any antenna is in the high current portion next to the feedpoint. The lower current end portions don't radiate much, they more-or-less cancel the reactance of the high current portions providing a good match to a practical feedline.

  If I understand you, you want something like a 40 meter dipole, running N/S, with each side running 20 feet straight out from the feedpoint, and the other 12 feet or so on each end pointing due east. That would wind up with pretty much a standard E/W "dipole doughnut" radiation pattern with a very small amount of extra radiation N/S.

The effects on radiation pattern and feedpoint impedance will be small, especially compared to the effect of ground height on that impedance.

Will it work? Yes, quite well. BUT - cut it long and trim it to resonance, because I suspect that you will need another foot or two on each end of the wire to achieve resonance.

73  Pete Allen  AC5E
Logged
Guest

« Reply #2 on: February 16, 2002, 05:54:43 PM »

Hi Pete, what I have in mind is the wires slanting from the feedpoint in the form of a v at between 90 degs. to say 120 degs.   Bill
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #3 on: February 16, 2002, 08:07:28 PM »

Hi Bill: If it's resonant, the same total amount of energy will be radiated as with a straight dipole. If it's high, in wavelengths, there will be some slight gain along the axis of the V - provided the angle is close enough.

And if the wires are several wavelengths long, and the wires are close enough, there can be considerable gain. That's why they call 'em "vee beams."

For those of us blessed with "city lot itis" the story is different. While the purists who think a tenth or two tenths of a dB is a major gain, or loss, will disagree - a half wave antenna needs to be a fair distance off the ground to have a pattern at all.

 Those of us who lack tall antenna supports will invariably wind up with a mushroom shaped radiation pattern that won't look much different from a low, straight dipole's pattern at the same height.

  I'm another of those who doesn't have enough room to stretch a 75 Meter dipole, but I wanted a 160 M dipole. I found a "Kansas Dipole" from Antennas West that I bent 90 degrees at the feedpoint, going 65 feet N/S across my lot and 65 feet E/W into a neighbors tree. The feedpoint is at 35 feet, each end is at 20. It works fine, but comparing reception reports with a friend whose 75 M dipole is at 50 feet, about a mile away, we have exactly the same 75 Meter results. If I work the DX he works 'em right after me, or vice versa.
 
  Hope this helps

  73  Pete Allen  AC5E
Logged
WB2WIK
Member

Posts: 21753




Ignore
« Reply #4 on: February 18, 2002, 11:11:14 AM »

It's good to remember that any gain picked up in a favored direction is the result of energy lost in some other direction(s).  If you cannot rotate the resulting "mini vee-beam" you describe, and you want to be able to make contacts in all directions, this arrangement is less than optimum.

Of course, if that's all the room you have, and you have no other options for installing the antenna, then obviously any wire orientation is better than no wire at all.

You can model various results achievable using the demo version of EZNEC, downloadable from their website.

WB2WIK/6
Logged
WB6BYU
Member

Posts: 17064




Ignore
« Reply #5 on: February 20, 2002, 11:47:22 AM »

If you are using a half-wave dipole, you won't notice much change
in the pattern from bending it in the middle.  And even less so when
using at low heights on 80m.  It should work just fine.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!