That is correct Bill. Unless the delay is significant relative to
the rise time of the signal, you will never know the difference.
If you were phasing NTSC video transmitters or high bit rate
digital data signals, it would be a consideration. For 3 KHz,
SSB - no problem!
73 de Mike, W4EF.............
----- Original Message -----
From: "Bill Tippett" <btippett@alum.mit.edu>
To: <sm2ekm@telia.com>; <towertalk@contesting.com>
Sent: Thursday, August 22, 2002 10:23 AM
Subject: Re: [Towertalk] Re: Phasing Lines For Stacks
> 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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