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: 20 meter dipole (with or without a balun) ?  (Read 1244 times)
WALTERB
Member

Posts: 528




Ignore
« on: April 18, 2012, 11:47:31 AM »

I believe I should be using a balun (4:1) for my dipole which is fed with RG-213.

Would it work better without a balun?

thanks
Logged
W0BTU
Member

Posts: 1577


WWW

Ignore
« Reply #1 on: April 18, 2012, 11:56:19 AM »

If it's a half-wave dipole, why would you use a 4:1 balun with coax? You would only use a 4:1 balun to match an impedance that's ~4 times higher or lower.

What you want is a good current choke, which is effectively a 1:1 balun. It will keep undesired currents off the coax shield, and keep the shield from picking up RFI.

I highly recommend that you read the excellent material on baluns and chokes on K9YC's site at http://audiosystemsgroup.com/publish.htm.
Logged

WX7G
Member

Posts: 5920




Ignore
« Reply #2 on: April 18, 2012, 11:56:51 AM »

If you use a balun with 50 ohm coaxial cable the balun should be a 1:1 current balun. Otherwise feed it without a balun.
Logged
WALTERB
Member

Posts: 528




Ignore
« Reply #3 on: April 18, 2012, 12:04:15 PM »

If it's a half-wave dipole, why would you use a 4:1 balun with coax? You would only use a 4:1 balun to match an impedance that's ~4 times higher or lower.

What you want is a good current choke, which is effectively a 1:1 balun. It will keep undesired currents off the coax shield, and keep the shield from picking up RFI.

I highly recommend that you read the excellent material on baluns and chokes on K9YC's site at http://audiosystemsgroup.com/publish.htm.

Yes, it would be a half wave dipole with each leg about 16.5 feet long.

thanks
Logged
WALTERB
Member

Posts: 528




Ignore
« Reply #4 on: April 18, 2012, 12:06:28 PM »

actually it will be fed with RG-8X.  I decided since its such a short run (< 50 feet).

Logged
WB6BYU
Member

Posts: 13038




Ignore
« Reply #5 on: April 18, 2012, 12:42:51 PM »

The SWR will be higher if you use a 4 : 1 balun than if you feed it directly.  That's because
the dipole impedance is close to 50 ohms, and a 4 : 1 balun is designed to match 200 ohms.

Use a 1 : 1 current balun if you are going to use anything.

The dipole may work just fine without a balun, depending on a  number of factors including
the length of the coax and what else is connected to the coax shield at the station.  And
performance can shift if there are any changes.  A balun makes behavior more predictable.  It
isn't required - don't let the lack of a balun keep you from getting on the air - but it increases
your chances that the antenna will work properly without adverse effects.
Logged
WA8UEG
Member

Posts: 339




Ignore
« Reply #6 on: April 18, 2012, 01:35:21 PM »

Have used 1/2 wave dipoles fed with 52 ohm coax since 1964, never used a balun never had an issue.
Logged
WALTERB
Member

Posts: 528




Ignore
« Reply #7 on: April 18, 2012, 01:54:05 PM »

ok, thanks to all!
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!