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[Towertalk] Re: Re: Phasing Lines For Stacks

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Subject: [Towertalk] Re: Re: Phasing Lines For Stacks
From: (Jan Erik Holm)
Date: Thu, 22 Aug 2002 20:20:08 +0200
Yes Bill I see it now, thank´s for the explanation. I sure was
wrong on this one, life is tough!

73 Jim SM2EKM

Bill Tippett wrote:

>SM2EKM wrote:
>>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.
>Hi Jim!
>        This bothered me a little too but I believe I have the
>answer.  Consider a CW signal split to 2 phase lines, 1 wl to
>antenna A and 2 wl to antenna B.  Under steady-state, both
>signals are in phase because phase repeats every 360 degrees.
>However, they are time-shifted by one period (35 nanoseconds
>at 28.4 MHz).  This means antenna A radiates the signal
>by itself for the first period, and antenna B radiates the
>signal by itself for the last period.  For all periods between,
>the signal is the combination and the result is "in-phase".
>Since we are talking about a CW, there is no distortion caused
>by combining two time-shifted CW signals, and I doubt we would
>ever notice the first or last 35 nanosecond periods when the
>signals from the two antennas are separated.  
>        For SSB, it is a little more complex since the signal
>is time-varying with the modulation.  However, since the maximum
>modulation bandwidth for SSB is around 3 kHz (333 microsecond
>period), any distortion from combining signals shifted by one
>period (35 nanoseconds) should not be noticeable to humans.
>        EZNEC verifies that there is no difference in far-field
>patterns between phasing of 0/0/0 and 0/360/720 degrees for the
>3 antennas in my stack, but I am sure EZNEC assumes steady-state
>conditions, and not the case of the first and last signal periods
>covered above.  Hope my simple-minded explanation helps!
>                                         73,  Bill  W4ZV

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