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Author Topic: RF leakage question  (Read 582 times)
KJ6CZS
Member

Posts: 15




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« on: November 04, 2012, 11:02:33 AM »

I don't know if this is a grounding issue, or what.  But I have an arrow antenna jpole that is hooked up to my kenwood D710 via a 50ohm coax that I bought from HRO then its connected via my switched powersupply and rigrunner.  The arrow antenna is not grounded.  When I was doing a net for my local ares/races, I noticed some stray voltage on the metal part of the microphone. Is that RF on the transmition line?  Do I need a line isolator?  I have the farrat that came with the D710, but it seems something is obviously wrong..

I know, I should know better, but don't want to buy a line isolator if its not needed.  The D710 is only 2m and .70cm... I felt the voltage on 2m.

Thanks to all for reading.. Much apprecited!

Newbie 73

kj6czs
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W6EM
Member

Posts: 727




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« Reply #1 on: November 04, 2012, 01:57:39 PM »

By your description, it sounds like the voltage appeared when you were transmitting.  Not there when just receiving.

Did you check the SWR on the line at the radio?  If you haven't, I'd suggest you do.  You could harm your radio if the SWR is high and you're long winded.

Always best to adjust a new antenna or at least check it first.
An MFJ antenna analyzer is a good tool to do that with also, since you can do it off the air.

If it turns out that you have some stray AC on the microphone, that's a whole nother can of worms.  Best to make sure you at least have a grounding conductor (green wire or round pin from the plug) on the supply from your outlet and that the supply ground is tied to the radio ground.  At least with no lightning in the area.

73,

Lee
W6EM

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G8HQP
Member

Posts: 120




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« Reply #2 on: November 05, 2012, 05:43:44 AM »

The J-pole antenna needs a balun if fed by coaxial cable, although for some reason many people seem to imagine it does not. Without a balun you will get RF current on the coax outer and that could find its way back into your shack. At VHF and higher frequencies you can't just attach a good ground to short out this current, as might work for HF.
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KB4QAA
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Posts: 2269




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« Reply #3 on: November 05, 2012, 12:01:59 PM »

Jpole antennas are notorious for common mode current on the feedline.   Another reason why a 1/4WL ground plane is a better choice!

As mentioned above you need to need some sort of choke/balun (depending on your feedline type) at the feed point of the antenna.
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