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[Towertalk] Re: Phasing Lines For Stacks

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Subject: [Towertalk] Re: Phasing Lines For Stacks
From: (Jan Erik Holm)
Date: Thu, 22 Aug 2002 16:03:11 +0200
eeee hmmm, guys dont kill me now but to be in phase, and I
guess that´s what you want, the feedlines has to be EXACTLY
the same lenght.
They "don´t need to" be mults of electrical wl, they can be
whatever lenght, however it´s easier to control your impedances
if they are mults of electrical half waves since the cable wount
transform the impedance then.

73 Jim SM2EKM

PS Be careful so you don´t radiate all RF straight up.

Bill Tippett wrote:

>K4XS wrote:
>>The question however, is this. Must the two pieces of Heliax be exactly equal 
>in length?  Or, can they a multiple of a wavelength longer as measured by my 
>MFJ 259?  If so, do they have to be a full wavelength longer or can it be 
>just a multiple of a half wavelength?  My gut feeling tells me that 
>everything would be fine if added an extra full  electrical wavelength. I 
>think just using multiples half an electrical wavelength would put them into 
>out of phase.
>Hi Bill!
>        Your gut feel is correct.  A feedline 360 electrical degrees
>more than the others will work OK.  180 electrical degrees (0.5 wl)
>will put the antennas out-of-phase which is NOT what you want.
>        I very precisely matched the feedlines on my 3-stack using the 
>MFJ-259.  Later, I once was considering replacing my top KLM-610
>monobander with a KT-34XA, so I modeled everything to try to understand
>what the effect would be due to the booms not being the same length and
>the feedpoint not being physically in the same place.  I discovered
>phase match is NOT very critical as long as it is within about 10 degrees
>(I think the number may be closer to 30 but I didn't keep my data).
>        If I were you, I would first carefully measure the velocity 
>factor of your hardline (each one separately if they are from different
>material).  Then simply calculate the additional length of feedline
>for 360 electrical degrees using [(983.56/f) * Vf] where f = frequency
>in MHz and Vf = velocity factor.  For example, assuming 28.4 MHz and
>Vf of .87, you would need to make the longer feedline 30.13' longer
>than the short feedline.  Assuming you measure correctly, you could 
>have an error of +/- 30.13/36 or ~10" before you approached a 10 degree
>error.  If you are a purist, you can use your MFJ to match exactly, 
>but it is not nearly as critical as I once believed.
>                                            73,  Bill  W4ZV
>P.S.  For example, assuming phase shifts of 0, +10, and +20 degrees 
>for the 3 antennas going up my tower, gain only changes by a negligible
>-0.08 dB and vertical beamwidth decresases by a negligible 0.1 degrees.
>Self Supporting Towers, Wireless Weather Stations, see web site: 
>Call 888-333-9041 to place your order, mention you saw this ad and take an 
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