BALUNS FOR TUNERS

( another myth debunked! )

I PROBABLY WON'T MAKE MANY FRIENDS WITH

WHAT YOU ARE ABOUT TO READ ON THIS PAGE.  :-(

IN THE PAST, THE INTERNAL BALUNS FOUND


WITHIN MOST COMMERCIAL TUNERS WERE A DISASTER!

QUOTE FROM TOM RAUCH, W8JI*:

 

4:1 Baluns inside antenna tuners, which are usually voltage-type baluns, are generally poor performers when presented with mismatched loads. 1:1 current baluns are generally much more efficient and have a much wider operating impedance and frequency range.

 

Further:   4:1 balun or any voltage-type balun is the wrong choice for use with antenna tuners in multi-band dipole systems. Most tuners use them because they are cheap, easy to build, and because almost everyone else uses them.

 

*"Baluns: Choosing the Correct Balun" by Tom, W8JI

View  HERE.

FACT:

In General, the best type of balun to use for matching an unbalanced

(asymmetrical) antenna tuner to openwire feedline is a 1:1 Current Balun.

 

 

EXPLANATION BY G3TXQ:  HERE.

 

OF COURSE THERE ARE EXCEPTIONS:

 

Whenever you know the impedance of your antenna system at the point you will insert the balun, if that impedance (for the bands intended to be used) is a good match (i.e., SWR = 2:1 or less), then a balun with a high ratio (i.e., 4:1) may also be a good choice. 

 

EXAMPLES:  

  • Folded Dipole (impedance about 300 Ohms).  A 4:1 balun will give us a 1.5:1 SWR into this antenna.  It is OK as long as it is a good quality current balun. .....................................................................................
  • Off-Center-Fed Dipole (impedance varies by band but is usually in the range of 100 to 400 Ohms).  This is a 2:1 SWR range for a 4:1 balun fed with 50 Ohm coax.  Normally this will be OK.  Never-the-less, trouble can occur at higher power levels.  When that happens, use a 1:1 CMC choke in addition to the balun.  Attach the choke directly to the balun.

 

HOWEVER, if on some bands the SWR will be higher than 3:1, you can expect trouble with common mode current on those bands.  When running low power (i.e. 100w or less), the trouble may be insignificant, but when running high power, it can be monumental.  

 

INSTEAD:  Use a 1:1 Guanella balun and insert an additional 4:1 transformer between the balun and the feedline.  This transformer may be either a Ruthroff or Guanella (even single-core Guanella), because its only task is the impedance transformation.  The 1:1 Guanella will take care of the common mode current blocking.

 

 

DO NOT USE A 4:1 BALUN FOR THESE APPLICATIONS:

 

EXAMPLES:

  • 80m Dipole fed with openwire and used on 40m (impedance is about 60 Ohms on 80m, but *2000+ Ohms on 40m).  This is the wrong place to use a 4:1 or 6:1 balun and will result in severely degraded rejection of the common mode current.  DO NOT DO THIS (and do not listen to the people who tell you it is OK).  It only works OK when running very low power.
  • 40m Dipole fed with openwireand used on 80m (about 10 Ohms impedance).  The 4:1 balun transfers it downward to 2.5 Ohms -   THIS IS DISASTEROUS!  THIS IS WORST CASE.  DO NOT DO IT.  Use a good 1:1 current balun for this.

 

 *Impedance will also vary with the length of the feedline, but this is a realistic possible value.

 

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FOR SOME THINGS THERE ARE NO EXCEPTIONS:

 

NEVER, EVER USE JUST A VOLTAGE BALUN WITH YOUR TUNER.  NO EXCEPTIONS!

 

( ALWAYS Use a good quality Current Balun. ) 

 

CONCLUSION:

AS A GENERAL RULE, ALWAYS US A 1:1 CURRENT BALUN WITH YOUR TUNER!

 

As with all rules, there are exceptions,

but if you do not understand precisely what they are,

it is safer to use the 1:1 balun.

 

In my opinion, “using voltage baluns in antennas” and “using a 4:1 balun instead of a 1:1 balun for a tuner” are both in the same category that the statement “the world is flat” was in 1493. Although Christopher Columbus had proven that wrong one year earlier, most people still were not yet up to speed on the point.  ;-)

 

MORE INFO ON THIS HERE:  {TUNER BALUNS}