[Towertalk] Re: Phasing Lines For Stacks

[Jan Erik Holm]

eeee hmmm, guys dont kill me now but to be in phase, and I
guess thatīs what you want, the feedlines has to be EXACTLY
the same lenght.
They "donīt need to" be mults of electrical wl, they can be
whatever lenght, however itīs 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 donīt 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.
>
>
>        
>
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