To Ground J Pole?

[WQWI871]

I was thinking about putting a J Pole in the attic, just for times I need to lower the mast, which should only be for a couple days. I've read that J Poles should be grounded and I wanted some opinions on that.

 

PS: I was going to go with an aluminum than a copper. I'd rather thread thinner solid aluminum than to solder copper.

 

A side note, I was going to make a dual band 2m/70cm J Pole, but, does anyone have ideas on building a quad/tri/6m J Pole? Something not too long? I know lower frequency, longer length, but, even if It's just a 1/4 wave rather than 1/2 or full to save space. That's just a side note, though, and not the primary focus.

[SteveC7010]

I was thinking about putting a J Pole in the attic, just for times I need to lower the mast, which should only be for a couple days. I've read that J Poles should be grounded and I wanted some opinions on that.

 

A j-pole doesn't need a ground plane like a quarter wave does. But the coax shield from the antenna to the radio is a chassis ground. It's part of what makes the j-pole work so well.

 

Since you plan to place this in the attic, a ground for the mast as lightning protection probably is not necessary, and you probably won't need a lightning arrestor installed inline on the coax either. In fact, for an attic install, you really don't need a mast, at least in the traditional sense.

 

I have two j-poles from Ed Fong. They're a wire ladder designed to be installed inside thin wall PVC piping, and there is little chance of them being a lightning rod if I were to mount them on top of the house. I'd still place a lightning arrestor inline for outside use like that.

 

My amateur radio club uses a j-pole fabbed out of 600 ohm tv antenna lead. It's not in any kind of encasement. They just fasten it to a 15' pole with some rubber bands and tie the pole to one of the legs of an outdoor shelter. The only ground there is the coax from the antenna to the radio.

 

I would check continuity on the coax shield from the antenna to the radio just to be safe.

[WQWI871]

Thank you for your response. I should've mentioned that I was referring to RF ground than electrical ground. I just wanted to know if a J Pole would perform okay in the attic (especially considering the height is not that of the mast outside) with the J Pole just being connected to either wood or pvc, and if I did attempt an RF ground, would it make a difference. But, again, it should just be for a few days, because I kind of only plan on using it for when the mast is down unless another situation arises.

[SteveC7010]

Thank you for your response. I should've mentioned that I was referring to RF ground than electrical ground. I just wanted to know if a J Pole would perform okay in the attic (especially considering the height is not that of the mast outside) with the J Pole just being connected to either wood or pvc, and if I did attempt an RF ground, would it make a difference. But, again, it should just be for a few days, because I kind of only plan on using it for when the mast is down unless another situation arises.

 

No ground plane required for a J-pole. But the coax needs to return to the radio properly. I am not deeply schooled on antenna theory, but with the J-pole that proper coax return may actually be the rf ground.

[WQWI871]

Okay. Thank you for your response.

[Soladaddy]

My understanding is a j pole does not need a ground, but does need a RF choke on the coax near the antenna. I make a 4" loop of about 4 turns of the coax just under the coax connector.

[RCM]

There is no RF ground on a J pole. It is in reality an end-fed half wave antenna, fed with a quarter wave matching stub.

And that being the case, you can't make a quarter wave J pole. You can however bend it at a 90 degree angle, at the end of the matching stub where the radiator begins.

 

The reason a quarter wave antenna needs an "RF ground" is that it is only half of an antenna: the radials, RF ground lead or whatever you use forms the other half. A half wave antenna is a complete antenna, hence no grounding requirement.