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

Subject: Re: [TowerTalk] Two signals on the same frequency?
From: K8RI on TT <>
Date: Sun, 14 Aug 2011 18:05:16 -0400
List-post: <">>
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.


Roger (K8RI)

> 73, Jim K9YC
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