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Re: [TowerTalk] Two signals on the same frequency?

To: "'K8RI on TT'" <>, <>
Subject: Re: [TowerTalk] Two signals on the same frequency?
From: "Gary Schafer" <>
Date: Sun, 14 Aug 2011 19:09:31 -0400
List-post: <">>
A ham that I knew some years ago (an avid Do's) claimed that he and his
buddy across town would sometimes get on the same frequency and one would
zero beat the other by holding the telephone up to the speaker at one
station and to the mike at the other station as they were both keyed up.
Then one would talk into the mike and phone at the same time.

He claimed that in a pileup that neither could break by themselves, got done
easily with the two stations.

If you think about a stacked array with the ability to feed in phase or out
of phase, sometimes one is better than the other. It all depends on how the
two or more signals are arriving at the other end when there is diversity
When the array looks more like a point source then absolute phase is more
important. But I suspect that when there is significant separation in
antennas then arrival phase at the other end is not as predictable.

Gary  K4FMX

> -----Original Message-----
> From: [mailto:towertalk-
>] On Behalf Of K8RI on TT
> Sent: Sunday, August 14, 2011 6:05 PM
> To:
> Subject: Re: [TowerTalk] Two signals on the same frequency?
> On 8/14/2011 5:47 PM, Jim Brown wrote:
> > On 8/14/2011 2:23 PM, Jim Brown wrote:
> >> The short answer is that the
> >> signals from multiple antennas will ADD algebraically,
> > One VERY important point is that for the signals to ADD, they must be
> > SYCHRONOUS -- that is, on precisely the same frequency, coming from
> the
> > same oscillator.  In practical terms, this means a signal generated by
> a
> > single transmitter, then fed to two power amps that feed different
> > antennas. Or a single transmitter (with or without a single power
> amp),
> > split between multiple antennas.
> >
> > If the two signals were not synchronous (that is, from two independent
> > transmitters) their phase relationships will be random, and addition
> and
> > subtraction will be quite unstable and unpredictable.
> Even then the signals remain synchronous only if they travel equal
> distances to the antennas.  IOW same electrical length of coax between
> transmitter, splitter, and amps assuming no phase difference in the
> power divider. Then the same electrical distance of feed line to the
> antennas from the amps with no intervening hardware such as tuners.
> Maintaining true phase over distance even in split systems is, or can be
> a real PITA. <:-))  Fortunately, except in phased arrays (which are a
> bit forgiving), or selectable stacked arrays. This type of problem is
> rarely encountered in ham radio.
> 73
> Roger (K8RI)
> >
> > 73, Jim K9YC
> > _______________________________________________
> >
> >
> >
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