6:1 Balun

[KB3TQO]

anyone have plans for a 70cm 6:1 Balun?

 

[Captain Kilowatt]

Hmmmmm.....6:1 is an odd ball ratio. 4:1 is easy using a 1/2 wave coaxial balun. Question: why the need for a 6:1 balun? Usually at 70cm the balun losses outweigh the losses incurred by not using one.If you really need a balun you should be able to adjust the element length/spacing to allow for a 4:1 coaxial balun.

 

[KB3TQO]

Well, I'm working on a 70 cm Yagi. Feed is going to a folded dipole. I guess I could use another match. Never done this before, just playing around. How else could I do this? I would like for what ever I end up with to handle some power. Thanks for the fast reply.

 

[Mudfoot]

Is this the result of a calculation calling for a 6:1. What kind of antenna are we talking about?

 

[KB3TQO]

I'm working on a 70 cm Yagi. Feed is going to a folded dipole. At the feed point I should be looking at give or take 300 Ohms I think.

 

[Captain Kilowatt]

I'm working on a 70 cm Yagi. Feed is going to a folded dipole. At the feed point I should be looking at give or take 300 Ohms I think.

You will never see 300 ohms at the feedpoint. A single folded dipole in feedpoint will present an impedance of 300 ohms but the minute you start adding parasitic elements that feed impedance is going to go down. Usually a 4:1 coaxial balun is used at the feedpoint. If you can measure the feedpoint impedance, I would suggest that you build the antenna close to what you want and then see what the feed impedance is and work from there. Starting off assuming the feed impedance will be 300 ohms just because the driven element is a folded dipole is not the way to start as it will never be 300 ohms once it is "absorbed" into the entire array.

 

[KB3TQO]

OK, Thanks for the info. That gives me a good starting point.

 

[Captain Kilowatt]

Coaxial balun info.

http://www.qsl.net/i0jx/balun.pdf

When I built my 6m yagi I used the 1/2 wave coaxial balun and a hairpin (Beta) match. I insulated the center of the element and mounted a bracket with three SO-239 jacks on it to connect the pieces of coax cable too. that made waterproofing it much easier than cutting back the shield and dealing with that. You will HAVE to do that on 70cm as even a small amount of shield and exposed center conductor will add a considerable amount to the length of the antenna element.

 

[HomerBB]

I agree with everything you fellows have said so far. If you change our minds let me know.