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

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Fan Dipole Question...  (Read 1295 times)
NK7Z
Member

Posts: 799


WWW

Ignore
« on: October 15, 2012, 09:46:28 AM »

Hi,
I will have a new tower up soon and want to add a dipole to the top of it...  I am considering building a FAN DIPOLE for the following frequencies:  10 MHz, 18 MHz. 24 MHz. and 50 MHz.  I assume I just cut dipoles for each freq, tie them all together at the center, then fan them out...  Balun of course...  Are there any issues other than harmonic radiation on 50 MHz. or 24 MHz. I should be worried about?

73's
Logged

Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
K2DC
Member

Posts: 1365


WWW

Ignore
« Reply #1 on: October 15, 2012, 10:03:37 AM »

Tuning and pruning can be a little ticklish due to interaction between the antennas.  You might want to look here for some construction tips:

http://www.hamuniverse.com/multidipole.html

Pay attention to the spacing between the bands both at the feedpoint and the ends.  Also that the final lengths may be something other than 468/F.  You should probably start with up to 10% more wire for each leg and prune back from there as required.  I've also seen a suggestion that you should match the lowest band first and work your way up in frequency from there.

73,

Don, K2DC
Logged
N4UM
Member

Posts: 474




Ignore
« Reply #2 on: October 15, 2012, 10:09:52 AM »

My advice:  Start by making them all longer than normally called for.  Try to minimize coupling between them.  This means putting them at right angles to each other.  Of course, with more than two bands this is impossible.  Begin pruning the antenna for the lowest frequency first, then the next lowest etc.  This is exactly opposite to how you would tune a trap antenna.
Logged
W9GB
Member

Posts: 2623




Ignore
« Reply #3 on: October 15, 2012, 10:38:40 AM »

Quote from: nk7z
I am considering building a FAN DIPOLE for the following frequencies:  10 MHz, 18 MHz. 24 MHz. and 50 MHz.  
Dave --

As you tune (cut) dipole (1/2-wave) wire lengths, be very AWARE of TWO 3/2-wavelengths in your antenna.

30 meters (10.1 MHz) ---> 3/2-wave at 30.3 MHz, just outside 10 meters
17 meters (18.068 MHz) ---> 3/2-wave at 54.204 MHz, just outside 6 meters

The 30 meters (10.1 MHz) also presents a 5/2-wave at 50.5 MHz (6 meters), which you may not detect.
You can easily mistake the wrong tuning point, if you are not watching OR using inaccurate test equipment.
« Last Edit: October 15, 2012, 10:43:19 AM by W9GB » 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!