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: Detuning effect of trees in a mobile installation  (Read 354 times)
VK2JAF
Member

Posts: 5


WWW

Ignore
« on: February 01, 2009, 02:05:12 AM »

Hello from Down under,

Just playing with mobile installation, and am noticing the effect of low hanging trees affecting "tunability" of mobile antennas for mobile installations..

Icom 7000..various commercial antennas..if in open can tune OK, however if sitting under low hanging trees..difficulty encountered..

be interested in any information on this topic,

regards,

Derek VK2JAF
Logged
K0BG
Member

Posts: 9878


WWW

Ignore
« Reply #1 on: February 01, 2009, 05:56:09 AM »

This happens to EVERY antenna, it's more noticeable in mobile antennas because they are mobile.

Probably the largest effect is caused by driveways that are steel reenforced. Most neophyte operators don't think about the metal under their feet so to speak, and they tune up the antenna perfectly. They pull out into the street, and now the SWR is too high.

Both of these are caused by capacitance, albeit the effects are actually on opposite ends of the antenna. The trees effect the capacitance at the top end, and the steel in the driveway on the lower end, of ground loss if you please. Ground loss, incidentally, is the largest factor a mobile operator has to contend with.

Alan,KØBG
www.k0bg.com
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!