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True Ladder Line and Wire Antennas

Don't I Need a 12:1 Balun to Convert 600Ω to 50Ω?

Posted by Brian Duerr WB2JIX on

I get that question quite often and it's pretty difficult for many hams to try to comprehend the use of a non-resonant antenna system. All we are conditioned to think about is 50 ohm cable, a matched, resonant antenna and attempting to tune for that perfect 1:1 SWR. Here's just a copy/paste response to an email I received recently.

Keep in mind, it's not an all inclusive answer and it IS far more involved than what I portray it to be. Visit my FAQ page

True Ladder Line FAQ's for some excellent links to relevant content.

Here's my response:

Yes, that's a common misconception, with many hams. Most actually.

We are not simply "dividing 600 by four" when we use a 4:1 balun. In fact, we may likely never even encounter an impedance of 600 ohms on any of the frequencies we attempt to tune with our transmatch.

We are so used to thinking of a 50 ohm, resonant antenna. If we have a 40M dipole and trim it perfectly for the center of the band, AND we can possibly achieve a perfect match at resonance, the feedline and the antenna at that single frequency, will present an SWR of 1:1 and 50 ohms at the transmitter. Now we move off frequency by a couple of KC and we're no longer at 50 ohms or 1:1, hence a higher SWR. We still have 50 ohm coax but it's certainly not at 50 ohms to the transmitter any longer. Now we've introduced some losses into the coax, in the form of heat.

The beauty of true open wire line is that you can have a 10:1 SWR and still be very efficient with extremely low losses.

Visit my FAQ page, where I have several links to some very good info and a lot of reading. True Ladder Line FAQ's

Within reason, with an open wire fed doublet, I don't care what the SWR is, I don't care what the impedance is and I don't care what frequency I am loading up on. None of my frequencies or bands, will ever be at resonance. It doesn't matter. We rely on the tuner to handle all the work. It's truly a "system", comprised of the tuner, the feedline and the flat top pieces. Everything works together. I generally try to use a balanced input tuner to avoid the extra balun.

However, I do have hundreds of customers that use a 4:1 balun with a decent quality tuner to achieve an excellent match on all bands. As I am the third owner of True Ladder Line, I rely on the help of Bob Rumsey at Balun Designs. He tells me that in nearly 95% of ALL customers with the previous owners, a 4:1 balun was used.

Feel free to contact me to answer any questions you may have to help you with your purchase. I get so many emails that if you want to contact me simply to stir up the old balun argument, I may not respond. Been there; Done that!

Thanks again............

Brian Duerr

WB2JIX, LLC

206 Conway Road

Starksboro, VT 05487

(802) 598-6825 Cell

http://www.trueladderline.com

  • balun
  • 4:1 Balun
  • 12:1 Balun
  • Resonant Antenna
  • Impedance
  • Dipole
  • Doublet
  • 600 Ohms
  • 50 ohms
  • SWR