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: RF Radiation from Balanced Feed Line  (Read 578 times)
KE4BIW
Member

Posts: 41




Ignore
« on: January 22, 2008, 09:47:10 AM »

I'm contemplating using a tuner for HF that has a balanced line output. It would be used to feed a dipole. I have three questions for the experts

1. Does the feed line radiate any RF? (I'm worried about RF in the shack)

2. Is a run of 100 ft. of feedline considered too long?

3. Is there any special treatment required for the feedline? For instance, once I exit the house can I just run it along the ground like I do now with coax?


Thanks for any input!!

de

KE4BIW
Logged
K5LXP
Member

Posts: 4536


WWW

Ignore
« Reply #1 on: January 22, 2008, 11:10:46 AM »

1. As long as you don't do anything to disturb the current balance between the two conductors, the field won't extend very far from the line.  If it becomes unbalanced due to uneven radiator lengths or effects from proximity to other conductors, then it will start to radiate.

If you're worried about RF in the shack, then why are you entertaining the idea of a random doublet fed with balanced line, and fed with a tuner?  Kinda like worrying about getting wet, then going outside when it's raining...


2. Only if your antenna is less than 100ft away.  Even under severe mismatch, 100ft would still exhibit low loss.
 

3. Absolutely.  It is sensitive to ground and nearby conductors.  Try to keep the line as far as practical from other objects, especially conductors.  6" is about as close to anything else as I'd run it.


Mark K5LXP
Albuquerque, NM
Logged
AA4PB
Member

Posts: 13032




Ignore
« Reply #2 on: January 22, 2008, 01:13:20 PM »

The RF in the shack issue will be helped if you can locate the tuner right close to where the feed line exits the building. Minimizing the amount of balanced feed line inside will minimize the RF in the shack.
Logged
N3BIF
Member

Posts: 1190




Ignore
« Reply #3 on: January 22, 2008, 09:45:00 PM »

 All of my HF antennas are hooked up with balanced line. The lines run from my tuner, which is on top of my main rig, straight up a cinder block wall to grade and then exit the house going over the water supply lines and through aluminum siding. These lines ( 5 or 6) then depart the house in whatever direction is needed to get to whatever antenna they are hooked to. One goes straight up the siding to my loop, Others head out across the yard running along the ground some more then 100 feet. They run through mud, dirt, snow, grass, leaves, bushes, trees, you name it. My PC sits 3 feet from the tuner, my monitor sits 3 inches from the tuner, I have 2 stereo amplifiers within  18 inches, RF is never a factor, My output however is limited to 100 watts,  Try the simplest set up first it may work for you like it has for me.
Logged
WA7NCL
Member

Posts: 625




Ignore
« Reply #4 on: January 24, 2008, 11:30:55 AM »

It shouldn't radiate if the tuner is balanced and antenna is symetrical.  If you do get some RF on rig and coax to it, use a line isolator or add a ferrite toroid to the coax feeding the tuner.  I use balanced line and it works pretty well on all bands.

One thing you can't do is run it on the ground.  The dirt and wet, cause line losses.  Run it above the ground at 10 feet higher if possible.  Just don't lay it on the ground.

If you have a wide range tuner, you will be happy with it, even with a long run to the antenna. You most likely can tune any band that your antenna is a half wave or greater on.  Sometimes you can go one band lower.

Try it, you will probably like it.
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!