Homemade UHF/440Mhz Amateur Radio Repeater Duplexer
Ham Radio Home Duplexer Tuning Guide
Here are some photos of a UHF Duplexer that I made.
The outer shell is aluminum 3 7/8 ID X 8in high.
The top plates are 1/8" aluminum scraps that I had laying aroung.
The copper pipe is 6" X 3/4" OD pipe. (don't make it too short)
The notch capacitor is high Q type.
The copper plate is circuit board (or flashing) and is bolted with a 1/4" bolt to the center of the top plate for stability.
Don't overheat the circuit board when soldering the main rod to the copper plate.
The loop is copper flashing 1/4" wide. 3/4" X 1/2" X 3/4" bends.
The end closest to the rod is between 1/4" and 1/2" away from the rod.
Note that this duplexer tunes by a fringing capacitance at the other end of the can.
This eliminates finger stock typically used and the noise introduced by it.
This design has anywhere from 70db to 90db notches and about 1.5db loss.
All drilling was done by hand so don't complain about the workmanship.
You will need a spectrum analyzer to tune this correctly or use the Poor man's Repeater Duplexer Tuning Guide.
This is the same design used on the 442.575 repeater seen on the previous page.

Inside of a single "can"
Capacitor for tuning the bandpass response
Assembled units