De-coupling transformer

[wbswetnam]

Is it always necessary (from a safety standpoint) to use a decoupling transformer? I have plans to mount a 2m J-pole (probably in the attic) so must I connect a decoupling transformer just before the radio (a Yaesu 857D) for 2m work? Or can I get by without it since it will be attic-mounted?

 

[LtDoc]

I take it a "decoupling transformer" is a balun, right? If so, then by going by the definition of a balun then no, they are not always needed. In most cases, they aren't doing anything very practical. The impression I get from the antenna being in the attic, or outside, seems to have something to do with lightning protection? If so, then a balun is completely useless for that purpose.
If I'm misunderstanding your meaning, sorry 'bout that.
- 'Doc

 

[wbswetnam]

Yes, an UNUN balun. What I read says that its purpose is to keep RF from returning to the radio from the antenna, thus reducing any shock hazard. But, again, it will be in the attic so is that likely to happen (RF returning from the radio in an unsafe manner that is)?

 

[WA0CBW]

Some antennas, like the J-pole that operate without a ground plane can suffer from RF coming back down on the outside of the coax and cause RF in the shack. You can get a nasty shock if you happen to touch something grounded. The purpose of the "choke balun" is to prevent the RF from coming back down the outside of the coax. This has really nothing to do with lightning protection.
BB

 

[wbswetnam]

Several months ago, someone posted "You also need a balun with a J pole, they radiate off the coax like crazy!" OK, so maybe I should think about getting a 1:1 balun. Where do I attach the balun? At the SO-239 on the antenna take-off, or just before the SO-239 input of the radio?

 

[WA0CBW]

It would go at the antenna.
BB