The Hybrid Ring Diplexer (duplexer) is a strange device compared to the standard Band Pass or Reject type.  What makes it different is the circuit that creates the pass.  In common duplexer types, the pass is either created by the band pass effect of a dual coupling loop cavity or the pseudo pass effect of a single loop cavity in BpBr, or the skirt leading up to the notch in a reject type cavity.  The hybrid ring creates the pass effect from the primary characteristics of a large notch cavity, but you are probably wondering how a notch cavity can create a pass effect.

The hybrid ring consists of several sections of coaxial cable, usually of a double shielded nature like RG-214.  The sections of the cable are electrically multiples of a 1/4 wavelength (in coaxial cable).  RF energy on the design frequency is injected into a Tee connector and split into two (unequal) paths then recombined back into one connection point with another Tee.  One path is electrically longer than the other, by 1/2 wavelength.  Since one path is 1/2 wavelength longer, power split at the originating Tee is simply canceled out at the terminating tee. Why? Because one path is 180 degrees out of phase with the other, all power close to the design frequency is canceled out at the combining termination.  Still with me?  Good.  Now lets insert a notch cavity, tuned to the design pass frequency, into one of the two paths.  By doing so, power being notched out of one path eliminates the canceling effect; which results in most of the originating power being transferred to the termination by the other path.  The neat part of this whole scenario is a Band Pass circuit is created that has the inverted characteristics of a notch cavity; sharp pass peak and steep skirts.  As in any cavity, the amount of coupling determines the bandpass width and insertion loss.  Due to the circuit, a pass response that has very defined width and loss results.

The Hybrid Ring Duplexer was a creation of the late Gilbert L. Boelke, W2EUP.  Gil was a very gifted and talented RF design engineer, and had become a friend of mine just before his passing.  Gil sold the concept of the Hybrid Ring Duplexer to Sinclair Technologies many years ago, but he was the only man I knew who could explain it in a language I could understand.  Presented below are articles that help explain in further detail the concept and engineering behind the Hybrid Ring Duplexer.  I hope this information allows you to see how neat this circuit really is.

Hybrid Ring Diplexer (Duplexer) Explanation (in PDF) by Gilbert L. Boelke  W2EUP - SK
Hybrid Ring Duplexer Tuning Instructions (Manual CM-106) by Sinclair Technologies
 
 
 

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