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Dorsey Fahlstedt wrote:
>>If you have a transformer with a center tapped secondary, (or two 
>> secondaries that can be wired this way), then with one RC network, you 
>> can generate a signal with 0 to 180 degrees of phase shift.
>>
>> Label the secondary as X = top, Y = center tap and Z = bottom.
>>
>> Place a resistor from X to a capacitor that then goes to Z. Label the rc  
>>junction as the Output.
>>
>>Take your signal from Y to the  Output.  As the resistor value is 
>>adjusted, the phase *relative to one  end of the transformer* will vary 
>>from in phase to 180 degrees out of  phase.  Somewhere in the "middle" 
>>will be found the 90 degree  point.
>>
> 
> 
> 
> 
> Do you have some theory behind this? I would like to understand how
> it works before building it.
> thanx.

I'm not so great at explaining this stuff but maybe a graphic analysis 
will help.  In the attached gif, the bottom line X-Y-Z represents the 
center tapped secondary.  VR is the voltage on the resistor, VC is the 
voltage on the capacitor and VO is the output voltage.

The phase angle is ALPHA.  As the R and C values change (for a fixed 
input frequency), the VO vector will sweep out a 180 degree angle. 
THETA represents the phase angle obtained from just the RC components.

If anyone sees a mistake here, please by all means, point it out.

Derivation of the pertinent equations is left as an exercise for the 
student.


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