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## Re: [TowerTalk] Pattern Distortion caused by faulty balun?

 Subject: Re: [TowerTalk] Pattern Distortion caused by faulty balun? Steve Hunt Mon, 02 Jan 2012 08:32:58 +0000 mailto:towertalk@contesting.com>
 ```John, All that I've ever measured lie in the range 0.95 to 0.99. Did you notice that I said *COMMON-MODE* velocity factor? Signals flowing on the outside of the braid are Common-Mode signals - signals on the inside are Differential-Mode; they can have totally different velocity factors. 73, Steve G3TXQ On 02/01/2012 02:41, john@kk9a.com wrote: > What coax cable has a velocity factor of> 95? > > > To: towertalk@contesting.com > Subject: Re: [TowerTalk] Pattern Distortion caused by faulty balun? > From: Steve Hunt > Date: Sun, 01 Jan 2012 21:57:54 +0000 > > Tony, > > It would be the length from the feedpoint to the ground; you also need > to factor in the Common-Mode velocity factor of the line - probably in > the range 0.95 to 0.99. > > If I model that feedline length connected to a half-wave 20m dipole, > assume a velocity factor of about 0.97 and a ground connection > resistance of 10 Ohms, I get 40% of the leg current flowing back down > the shield as CM current. > > If you are trying to estimate whether or not the conducted CM impedance > is high or low at the feedpoint, remember you need to do it for all > bands on a multiband antenna! > > 73, > Steve G3TXQ > > On 01/01/2012 21:30, Tony wrote: >> The total length of feed line to the rig is about 85 feet. It's >> grounded at 70 feet where it then goes into the shack using a 15 foot >> jumper. Which do you take into account as being a multiple of >> half-wave? The total length of the coax or the length between the >> antenna and ground? Tony > _______________________________________________ > > > > _______________________________________________ > 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 ```
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