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Balun: top or bottom of ladder line?

Mar 4th, 01:00

K7RMA

Joined: Jan 10th 2013, 23:05
Total Topics: 0
Total Posts: 0
Hello all,
I've listened on portables for years, but just passed my tech exam and upgraded my equipment. A HOA restricts what type of antenna I can use, so I'm running a Cobra Ultralite Senior dipole as an inverted V, hoping the HOA won't spot it. The Cobra comes with fantastic weatherproof ladder line, which I'm thankful for given the two environments I call home (rainy Oregon and scorching Arizona). Now here's the question: I know a dipole will need a balun, but I've seen conflicting advice on where it should be placed. Here are my three options as I see them:

1) Place the balun at the apex of the inverted V I could put it in series with the ladder line, then run the ladder line indoors to a PL259 and my low-pass filter.
2) Place the balun indoors at the end of the ladder line, so it is between the ladder line and a length of coax to the low-pass.
3) Place the balun at the apex of the inverted V and run coax all the way up to it, eliminating the ladder line altogether.

Clearly Option 3 is not the way I want to go. Among other advantages, I can run ladder line under a window without drilling any holes in the wall. But placement of the balun, at top or bottom of the ladder line, is the question of the day. I appreciate any suggestions!

Thanks and 73s.

Mar 4th, 03:09

AA6E

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
The name "balun" tells you everything. It is a transformer that connects a balanced load (as your antenna and ladder line are supposed to be) to an unbalanced load (like coax should be). So your options 2 or 3 are possibilities, but not 1.

There is also the question what ratio the balun should have. Some of them are 1:1, for approximately 50 ohms balanced to 50 ohms unbalanced. Another common type is 4:1, converting 200 ohms balanced (like a folded dipole) to 50 ohms unbalanced. If you're operating a half-wave dipole or inverted V at its resonant frequency, a 1:1 unit is probably best.

If you're operating multibands, you might need to have an antenna tuner at your transmitter that will let you convert a wide range of impedances to 50 ohms. Some tuners will accept balanced line (ladder line) directly without an extra balun.

With antennas, it seems like nothing is simple. On the other hand, almost anything will radiate something!

73 Martin AA6E
Mar 4th, 18:53

K7RMA

Joined: Jan 10th 2013, 23:05
Total Topics: 0
Total Posts: 0
Thanks Martin, that says it all.
73,
Rob KG7JCJ

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