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: Multiple Mobile Antennas  (Read 443 times)
KB9YZL
Member

Posts: 16




Ignore
« on: April 23, 2003, 01:10:27 PM »

I currently work for the Meteorology Department of the local Community College as their "Radio Guy". (A position I fell into, due to my knowing just enough about radio gear to be a danger to myself.)

Over the past ten years, our mobile electronics have gone from a single CB, to the 11 antenna setup currently being worn by our lead van.  This setup includes two 2M sets, two CBs, three scanners, one TV, one GPS, and two cell phone antennas.  Aside from looking like a porcupine, everything seems to be functional, but I am concerned about interaction between the various sticks up there.

I have noticed significant changes in SWR when an antenna is evaluated individually, and then checked again as part of the whole setup.  It's not bad enough to keep me from keying up, but it's troubling to see an antenna go from 1.2:1 when measured alone, to 1.7:1 when it's part of the group.

I am not an electronics wizard, (obvious, isn't it?) so I'd like to hear some other opinions on the subject.  Thanks in advance!

Kent
KB9YZL
Logged
K0BG
Member

Posts: 9886


WWW

Ignore
« Reply #1 on: April 23, 2003, 03:22:26 PM »

The old cliché still stands: If it ain't broke don't fix it!

Yes, of course, there'll be interaction and I'm not surprised at the change in VSWR. it's a little late to think about this (lots of things grow like topsy) but if you knew from the onset you were going to put this many antennas on the van, then you could have placed them in such a way as to minimize interaction. but like I said, if it ain't.....


Alan, KØBG
Logged

KA5S
Member

Posts: 229




Ignore
« Reply #2 on: April 26, 2003, 11:05:00 PM »



Yes, they can detune each other. If your car roof is as small as mine it's worse, too.

I put antennas for the same bands (or multibanders covering the same bands) as far away from each other as possible. I use rigid antennas where wind might blow one into another, and if I can't do that, I tilt them so they don't bend that far. I use highpass and lowpass filters to keep out-of-band RF out of rigs that aren't transmitting. I use shorter antennas where I don't need gain, to reduce coupling.

(If you have rigs dedicated to particular services and you don't need every position to cover the whole high-band or UHF range, bandpass filters for the channels you DO use is a very good idea, if only to protect the radios.)

HF antenas with top-hats are quite sensitive to detuning from VHF antenas beneath or near the top-hat, so even though top hats would make for better signals, I am using only straight whips on my HF antennas.


Cortland
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!