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## Re: [TowerTalk] Stub question

 To: cgalbrai@umich.edu, ec1cwg@dxhunters.com,towertalk@contesting.com Re: [TowerTalk] Stub question "BRENT BAUM" Thu, 25 Jan 2007 13:51:28 -0700
 ```Chris, Will the choke and resistor techniques also work on wire dipoles? 73, K7MEI Brent``` From: "Christopher J Galbraith" To: "'EC1CT Fernando'" ,"'towertalk'" Subject: Re: [TowerTalk] Stub question Date: Thu, 25 Jan 2007 08:54:50 -0800 Hi Fernando, A 46 ft length of RG-8 (or other coax with 0.80 velocity factor) is a quarter wavelength at 3.75 MHz. If you connect one end to the antenna feedpoint (center conductor to vertical element, braid to radials) and short the other end, any DC (static charge) sees a short circuit (everywhere), but RF at 3.75 MHz (plus or minus about 10% or less) sees an open circuit at the antenna feedpoint. It's the magic of a quarter wave line (or the math of forward and reflected waves, whichever you prefer!). Other ways to bleed off static charge I can think of are: (1) use an RF choke across the feedpoint with a minimum value of about 22 uH (for a reactance of 10x 50 Ohms = 500 Ohms at 3.5 MHz) that has a self resonant frequency (SRF) higher than about 10 MHz. Note that this will only work on 80m; if you use the vertical on higher frequencies, the choke must have a SRF of about 3x the highest frequency used. ```(2) Put a 300 kOhm resistor (0.5 W rating) across the feedpoint. This will discharge static and your TX/RX won't know the difference. With 1500 W at the feedpoint, the resistor will dissipate 0.5 W (you can use a lower R for lower power levels). I use this method and it works FB.``` 73, Chris KA8WFC ```-----Original Message----- From: towertalk-bounces@contesting.com [mailto:towertalk-bounces@contesting.com] On Behalf Of EC1CT Fernando Sent: Thursday, January 25, 2007 8:01 AM To: towertalk Subject: [TowerTalk] Stub question``` Hello all, I recently aquired a quarter wave vertical for 80 meters. It´s a 33 ft aluminium mast with a capacity hat designed by EA5JK. It has such a kind of loading coil. Yesterday at the radio club someone told me to put a stub formed by 40 ft or so of coax line at the feedpoint. He said that would help me to prevent the static but this stub would put the antenna in shortcut as it would connect in any way the radial system with the copper core of the coax line to the radio. It doesn´t convince me at all. Just wondering if any of the low banders here have added any stub to their verticals and how you did it. Thanks a lot. 73s BTW: lot of snow in norther spain today. Prop is as bad as the weather.... EC1CT Fernando E-mail: ec1ct@ure.es _______________________________________________ ```_______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk``` _______________________________________________ ```_______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ``` ```_______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] Stub question, EC1CT Fernando Re: [TowerTalk] Stub question, Christopher J Galbraith Re: [TowerTalk] Stub question, BRENT BAUM <= Re: [TowerTalk] Stub question, EC1CT Fernando