Hi,
the explanation is more simple. On one frequency 1 OR 2 WL would be
almost OK, but the band is much wider, the bigger difference in the
cables you have the bigger difference in real electrical length you have
on the EDGES. The bands are a few percent wide do not forget this ! If you
have two cables of any length you have no difference on edges since the
cables are always the same which is significant. If you spend $hundreds
or better to say thousands on antennas why not spend another $tens on a
propper cable ?
73 !
Jiri
OK1RI
> 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
>
>
> _______________________________________________
> Self Supporting Towers, Wireless Weather Stations, see web site:
> http://www.mscomputer.com
> Call 888-333-9041 to place your order, mention you saw this ad and take an
> additional 5 percent off
> any weather station price.
> _______________________________________________
> Towertalk mailing list
> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
|