multiban dipole feed?

[kd6zxe]

Hello,

I recently constructed an antenna similar to this one:
http://www.hamuniverse.com/multidipole.html

There was no mention of a balun at the feed point, however I do now notice that they indicate separating the shielding and connecting each dipole at a different point along the length of several inches of unshielded cable.

In my attempts to make things "cleaner" I didn't cut up a piece of coax, but I did use a pl239 connector where all the dipoles meet. The attached images show the feed point inside the junction box and the finished antenna mounted on the roof. Note the roof is about four stories up, however at the end point (lowest part) of the 40m dipole is maybe a foot off the roof.

Some comments have been made that I should have fed the dipole using a 1:1 balun for various reasons, one of which to avoid arcing between the dipoles.

Any considerations I should really take into account for this antenna design? Modifications?

Thanks.

[jonny290]

Uh, what I wouldn't give for the view off that rooftop...

Anyways to do a decent HF choke balun, wind about 6-10 turns of your feed coax into a coil right at the antenna feed point, and secure it with tape. This'll keep RF off the shield, which is the most important use of a 1:1 balun.

[kd6zxe]

Originally Posted by jonny290

Uh, what I wouldn't give for the view off that rooftop...

Anyways to do a decent HF choke balun, wind about 6-10 turns of your feed coax into a coil right at the antenna feed point, and secure it with tape. This'll keep RF off the shield, which is the most important use of a 1:1 balun.

Here's the sunrise view off in the other direction, just in case the first pic wasnt cool enough I thought I'd make you more jealous..

6-10 turns of what diameter? or does it matter? Should they be all the same diameter or just close?

[k9rzz]

"The Ugly Balun"

http://www.hamuniverse.com/balun.html

Many variations.

[gcgrotz]

Arcing is not the reason to use a balun so don't worry. If you can redo the PL-259 at the feed point, you could get 10-12 ferrite beads that slip over the coax and then re-install the connector. I think you can buy it pre-made too. Prevents feedline radiation. If you make the coil, use black wire-ties, they last longer in the weather.

That's a pretty cool looking antenna!

[jonny290]

Originally Posted by gcgrotz

Arcing is not the reason to use a balun so don't worry. If you can redo the PL-259 at the feed point, you could get 10-12 ferrite beads that slip over the coax and then re-install the connector. I think you can buy it pre-made too. Prevents feedline radiation. If you make the coil, use black wire-ties, they last longer in the weather.

That's a pretty cool looking antenna!

This might be a better solution, as it doesn't require an extra 20 feet of feedline... plus those coax loops are a few pounds, puts extra weight up high (not always the best)


if you want you can create a 'choke jumper' with a few feet of RG-8 with the ferrites on there, then solder PL-259's on the end and connect the end of your feedline with a female-female barrel.

then you have a shield choke that you can move to another coax run without chopping it up added loss should be trivial at HF.