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Title: open wire stubs Post by: Steve W8TOW on March 12, 2007, 08:40:41 AM Just put up a " new" feeder system for my 1/2 wave CF Zepp.
SO... The old feeders were the "brown 450 ohm" stuff...1/2 wave feeder shorted at end, tap about 3/4 from feed point into the shack. After 8 years, I finally decided time for new feedline. SO... New W7FG 600 ohm open wire went up. But this time, using an online "Stub-calculator" I decided to get more accurate matching! Originally, I just hunted for the sweet spot to tap into the feeders.... And I decided to go with a 1/4 wave OPEN ended stub. Sure looks good but....LOTS more RF detected in the shack compared to the previous stub... Any ideas? 1) Not the right tap spot 2) More Rf is getting to antenna, so naturally more RF in shack 3) the "runs" of new feeders are closer to the shack by 10-15 feet so naturally, more RF nearby 4) I just don't know what I am doing! Any other ideas??? (OH, it loads great now, but havn't tried it on the air with the big rig....yet) vri 73 steve 8tow Title: Re: open wire stubs Post by: WA1GFZ on March 12, 2007, 02:45:04 PM if we all knew what we were doing there would be nothing to talk about here.
Title: Re: open wire stubs Post by: KF1Z on March 16, 2007, 07:40:27 AM So, this is a 1/2 wave dipole....
With a 1/4 wave stub.... Coax feed from the stub to the shack?? just curious......... Title: Re: open wire stubs Post by: Steve W8TOW on March 16, 2007, 08:44:49 AM Good morning! Little more info on the system here at 8TOW.
The antenna is a center fed 1/2 wave dipole (Zepp) using a 1/4 wave (open end) stub made from 600 ohm feeder. Then at approx 13 feet from the feed point, I have "tapped" into the stub with 600 ohm feeders into the shack... I did make some slight changes tho...The run of 600 ohm feedline to the shack was about 2 feet above the roof...now it is 5 feet ++ above the roof and my "RF" detected in the shack was minimized. I discovered that the wider the spacing the open wire, the greater the isolation from other objects you must have..! 73 steve Title: Re: open wire stubs Post by: WA1GFZ on March 16, 2007, 08:46:36 AM You might consider shorting the stub to see the effect....
Title: Re: open wire stubs Post by: Steve W8TOW on March 19, 2007, 08:43:55 AM Well, good news fellas...looks like we got a winner. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Again, CF Zepp, 1/4 wave open ended stub....600 ohm stub, 600 ohm feed into shack....The line from stub to shack is tapped at approximately 14' from antenna feedpoint with the 600 ohm open wire. Problem: More RF present on FS Meter in shack. Resolve: Elevate 600 ohm feeder from shack to stub higher above roof. I raised this feeder about 4 feet more...(it is now 6' above roof line and any object) . Then I did some on-the-air tests... Running 300 watts output, reports are improved... I installed a remote "sense" antenna for the FS meter about 100" from the shack yesterday. Wish I had done this with the old feeders but now I have a reference! 73 steve 8TOW |