Tuning Duplexers in the Geek Lab

One of the duplexers that had been pronounced as 'misbehaving' from the mountain top repeater was pulled down and delivered to the lab.  The first order of business was to take a look at it using the VNA (Vector Network Analyzer).

Initial findings for the duplexer were not great as can be seen in the response plot.  The bugs on the plot represent the receive and transmit frequencies for the repeater.

Tuning each section individually and then reconnecting them to view an over all plot produced a somewhat better response.  This particular duplexer includes a notch capacitor with each cavity. The bug for the receive frequency on the left is off by 200 Khz.  I'll let you know how the duplexer works when it is reinstalled back on the mountain.