Field adjusting your band pass/band reject duplexer for maximum performance 
 
Adjust the duplexer in the normal way on the bench. After you have them tuned using the 50-ohm terminators you are now ready to do the final tuning at the repeater site.  
Step (1) Connect the transmit side of the duplexer to the transmitter using the cable you intend to use on the repeater and connect the antenna. Connect the receive side of the duplexer to your service monitor using the cable you intend to use on the repeater. Set the service monitor for the transmit frequency. Put your repeater in transmit and adjust the notch on the receive cans for minimum signal on the service monitor, (best notch). Do the same on both cans (starting with the can at the antenna) if you have a 4-can duplexer. 
 
Step (2) Now turn the transmitter off and connect the service monitor to the transmitter cable and set for the receive frequency. You are replacing the transmitter with the service monitor. Connect a signal source (a mobile rig will work) to the receive side of the duplexer using the cable you intend to use on the repeater (the antenna stays connected). Set the signal source to the receive frequency and key it up. Adjust the notch on the transmit cans for minimum signal on the service monitor, (best notch). Do the same on both cans (starting with the can at the antenna) if you have a 4-can duplexer. 
 
That's all there is to it, just 2 simple steps. These simple steps will sometimes make a noticeable improvement in the operation of your repeater.  
You see the antenna is very rarely a pure 50-ohm resistive load so this little trick can some times make a big difference by matching the high Q duplexer notch to the load. That is if the load (antenna) is not to far off. 
You may also notice the major change in the notch will be on the can closest to the antenna. Remember you are transmitting into the antenna instead of a pure resistive load and at times will effect your system in ways you donít expect. 
Oh by the way please do not use a handy for your signal source. For one thing they are not a very clean signal sources and they just do not have the power you need to do the job. The signal source would be ideally one that can supply the same power level as your repeater transmitter.  
AS ALWAYS THE USE OF THIS INFORMATION IS AT YOUR OWN RISK!