EMRFD Message Archive 14145

Message Date From Subject
14145 2017-07-09 04:49:13 VU3SXN / KC3CWD requesting information on feeding balanced antenna with a L match at

I am trying to feed a resonant length 7 mhz full wave delta loop 41
meters of total length with an L-match ATU,

Since the l match is a non balance tuner and a full wave loop is a
balanced antenna , so can please provide few of your expert tips that
how can I feed this balanced loop antenna to a unbalanced l match
antenna tuner, I am planning to use this loop antenna on all the freq
from 7 to 30mhz will also try it on 6m,

I have few options in my mind but I am confused what arrangement to use..

Option1. Use a 1to1 current balun between loop antenna to l match tuner,

Option 2 use a 1to4 balun between loop antenna and l match tuner

Will these baluns feeding the loop antenna will be efficient as I use
homebrew rigs with 15watts output and I am trying to make it very
efficient ….

Vu3sxn / kc3cwd

Shubham tiwari
reply at -- vu3sxn@gmail.com

[Non-text portions of this message have been removed]
14146 2017-07-09 05:34:43 Nick Kennedy Re: requesting information on feeding balanced antenna with a L matc
I used a full wave loop a few decades ago.  At the time I didn't know enough about balanced and unbalanced to worry about it, so I just connected my coax directly to the feedpoint.  It worked very well. I can't say how much feeder radiation I might have had, but I didn't notice any ill effects.

So I'd suggest you start by doing the same. If you notice any common mode effects, add the choke balun (1:1). Since it won't hurt anything, you might put one on from the start.

Not sure I see any advantage of a 4:1. 


Nick, WA5BDU

14147 2017-07-09 05:55:34 jwolczanski Re: requesting information on feeding balanced antenna with a L matc
That's exactly what I use, an unbalanced L-network feeding a balanced antenna - in my case, a 40 meter dipole fed with open wire (4" spacing) line.  Works on all bands 40 - 10.  On 80, I tie the feeders together and treat the antenna as a top-loaded vertical.

The tuner must be floating from ground, and probably not adjacent to grounded objects.

My coupler has the inductor as the shunt element to give me some high-pass protection from a local 22kW AM Broadcast station.

If you use an L-network with a capacitor as the shunt element, a lot of schematics show a switch, whereby the capacitor can be attached to the antenna side (high Z), or the transmitter side (low Z).  I've done this, but never found a situation where the low-Z configuration was needed.  YMMV

Putting a BALUN on the antenna side of the coupler exposes the BALUN to a lot of stress.  Having the BALUN on the transmitter side where there is a matched condition seems best, but I've had really smart people disagree with me on this......

I've used 1:1 and 4:1 BALUNs but the 1:1 BALUN, at least in my case, works best.

As to what BALUN to use, I've used coax coil BALUNs and am currently using a FT240-43 core with about a dozen turns of small diameter coax wound on it.

If you are a ARRL member, the article entitled "Don't Blow up Your Balun", by Dean Straw (N6BV) in the June 2015 QST is illuminating.  The current ARRL antenna book describes his L-network tuner in more detail.

I've used a Johnson Matchbox, and home-brew Z-match, and plug-in coil couplers.  My L-network works as well as any of them.  I've recently built the balanced coupler described by VU2ESE (you can see it in my files) but found it would not work well on the higher bands, where a very fine inductor value was needed.

Good luck!
14148 2017-07-10 02:44:01 Sandeep Lohia Re: requesting information on feeding balanced antenna with a L matc