Topband: Goniometers and 160

[Tom Rauch]

Hi Ford,

> After doing a bunch of searching my literature and the web, nothing. 
> It seems to me to be a perfect approach to inserting a phase delay to
> phase antennas in a favored direction.  So little information appears
> available. Anybody got experience with these animals?

Goniometers do NOT, by themselves, vary phase delay. They vary 
amplitude ratio (mostly between adjacent inputs) and can flip-the-
phase 180 degrees on any given input group (when rotated 180 
degrees mechanically). 

They are mostly useful for nulling receive signals in a bidirectional 
pattern with broad lobes and a sharp null, like in DF'ing.      

> For those that don't have the reference, the basic design is to insert
> three coils, one inside the other.  Two are 90 degrees apart and fixed
> in position.  The third is rotatable to obtain a delay (apparently). 

That would be a two-pole. Mutual coupling varies as the 
"secondary" winding is rotated past the poles. The goniometer 
itself does not shift phase, other than a 180 flip. It only provides 
amplitude variation between adjacent inputs as it is rotated.

If we fed the input poles at 0 and 90 degrees, we could obtain a 
phase-shift of 0-90 degrees and 180 to 270 degrees but there would 
be considerable amplitude shift. We need more phases (and poles) 
to have complete phase rotation.

Continuously varying phase-delay, even just between two ports, 
while maintaining a reasonable SWR is a major undertaking. We 
also should remember in a phased-array suitable for transmitting 
(reasonable efficiency) impedance of each element varies greatly 
with phase-shift changes (being equal only at 0 and 180 degrees).

If we built something that worked we'd wind up with a VERY 
complex system, and have very little or no benefit with a simple 
system providing a few fixed directions. It certainly would not be a 
simple goniometer system! There are much better ways to solve 
the problem, but all are complex. 

73, Tom W8JI
w8ji@contesting.com


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