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Author Topic: RF Feedback?  (Read 1605 times)
KA9TZU
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Posts: 52




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« on: July 21, 2004, 03:00:12 AM »

I run a Yaesu FT-301 and with 2 different amplifiers, I have the same problem. When I tune into a dummyload, everything is perfect. When I switch to the antenna and key the radio, it goes to full output, even on SSB. (turning the mike all the way down does not help)It does not happen all the time, but enough to be a problem.

It used to only happen on 10 meters with my Imax 2000, but it happened on 80 meters tonight with my Alpha-Delta dipole and it is tuned down to 1:1 with an MFJ-989C. When it finally stopped after retuning the amp several times, the amp and radio received great signal reports. (Adjusting the tuned input circuit does not help)

The radio on it's own works great and I never have any problems.
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W8JI
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Posts: 9748


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« Reply #1 on: July 22, 2004, 03:06:13 PM »

The IMAX antenna lacks a ground. It is a VERY poor design.

Because it lacks a ground, you will have problems with RF on the coax shield getting back into your gear.

It is a typical CB antenna, overexaggerated gain claims and poor basic design. A 5/8th wl antenna actually has less gain than a 1/4 wl groundplane with drooping radials!

As for the other bands, a 1:1 SWr has nothing to do with RF feedback. Dipoles can require baluns, otherwise they also will have RF on the shield.

You could ground all your station gear together and install a good station ground or pepper your staion with snap-on beads, but the real cure would be in the antenna system.

By the way, check your jumper cable connections and make sure you don't have an open shield.

73 Tom  
   

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