Original Duplexer Configuration

Original Duplexer Photo 1
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Original Duplexer Photo 2
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Original Duplexer Photo 3
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These photos show the original configuration of the N6EX repeater duplexer. The transmit and receiver filter pairs used the original RG142 cables that came with the preselector panel. A bridle was constructed from UT141 (RG402) semi-rigid cable. This cable made the empirical derivation of the cable lengths easier than if standard flexible cable was used.

Duplexer Cable Lengths

Original Duplexer Cable Diagram
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The diagram to the left shows the original cable lengths used on the N6EX repeater duplexer. The diagram and included chart show the lengths between the two cavities (Bp and BpBr) on each side of the duplexer as well as lengths between the BpBr on each side and the Antenna Tee connector. The lengths are measured from the ends of the connectors.The cable between the pairs of cavities was RG142 and the cable between the cavities and the Tee was UT141. RG142 could be used in place of the UT141. The cable length should be same since both use teflon dielectric.

Duplexer Tuning/Performance

The procedure used to tune the duplexer is as follows:
  1. Tune individual cavity (Bp & BpBr)
  2. Connect pair of cavities and verify performance
  3. Connect two pairs to Tee and verify performance
An Agilent E5071B series network analyzer was used to tune and measure the duplexer. The coupling loops on the receive and transmit pass cavities were left in approximately the same positions as they were received, which yielded approximately 0.6 dB and 0.5 dB, respectively.

Receive Path Performance

Original Receive Pass Filter Plots
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Receive Pass Cavity
  • Approximately 0.6 dB insertion loss
  • 17 dB input return loss
  • 26 dB rejection at transmit frequency


Original Receive Pass-Reject Cavity Plots
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Receive Pass-Reject Cavity
  • Approximately 0.8 dB insertion loss
  • 28 dB input return loss
  • 55 dB rejection at transmit frequency


Original Receive Pass + Pass-Reject Cavity Plots
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Combined Receive Pass + Pass Reject Cavities
  • 1.6 dB insertion loss
  • 30 dB input return loss
  • >80 dB rejection at transmit frequency


Original Duplexer Total Receive Path Plots
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Total Duplexer Receive Path (at Tee)
  • 1.7 dB insertion loss
  • 20 dB input return loss
  • >80 dB rejection at transmit frequency


Transmit Path Performance

Original Transmit Pass Filter Plots
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Transmit Pass Cavity
  • Approximately 0.5 dB insertion loss
  • 20 dB input return loss
  • 23 dB rejection at receive frequency


Original Transmit Pass-Reject Cavity Plots
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Transmit Pass-Reject Cavity
  • Approximately 0.8 dB insertion loss
  • 19 dB input return loss
  • 52 dB rejection at receive frequency


Original Transmit Pass + Pass-Reject Cavity Plots
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Combined Transmit Pass + Pass Reject Cavities
  • 1.3 dB insertion loss
  • 21 dB input return loss
  • >80 dB rejection at receive frequency


Original Duplexer Total Transmit Path Plots
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Total Duplexer Transmit Path (at Tee)
  • 1.4 dB insertion loss
  • 27 dB input return loss
  • >80 dB rejection at receive frequency


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