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[TowerTalk] Adjustable Phase Shift networks

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Subject: [TowerTalk] Adjustable Phase Shift networks
From: (Tom Rauch)
Date: Wed, 25 Jul 2001 19:50:00 -0400
Hi Mel,

> When building a multi element array, I have had to put in odd phase shifts
> to properly achieve the pattern I wanted.  Using different lengths of feed
> line works, but is obviously difficult to adjust.  Anyone have a good

There are a dozen solutions, but remember these rules. If you use 
transmission lines:

A *mismatched* feedline only shifts phase the amount of the length 
when the line is an exact electrical multiple of 90 degrees. 

Be sure your feedlines are matched or you know the phase shift 
with the mismatch. If the line is mismatched and is not a multiple 
of 90 degrees, the phase shift is not equal to the line length in 

Maximum error is when the line is an odd-multiple of 45 degrees, 
and of course with the highest mismatch and longest lines. 

For example, a 135-degree long RG-8 line teminated in a 1.5:1 
resistive mismatch shifts phase 146 degrees. 

If you use a hybrid:

A hybrid only shifts phase the design amount when every port is 
perfectly matched and only at the design frequency.

There is no passive device available that splits power evenly into 
different load impedances. 

There is no minimum-loss continuously variable phase system that 
does not shift amplitude ratios when the lines are mismatched. 

> reference for designing adjustable feedline phase shift networks?  I
> vaguely remember an article (many moons ago) on doing so, but could not
> drag it out. Thanks.

You can use conventional T networks to vary phase and power 
division, or design the entire system.

You can use a BCD switched line (like a BCD switched set of lines 
in series 2, 4, 8, 16, 32 degrees long will give you every two 
degrees from zero to 62 degrees) to vary phase but you will have 
no control over power division and the phase will only be correct if 
the lines are matched. This is the system I use.

There is software that calculates phase shift of networks and 
transmission lines with various loads. KM5KG Grant Bingeman 
wrote some. I don't know if there is any freeware.

73, Tom W8JI 

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