Hello group, I have been working on building a duplexer for 222 MHz from old 150 MHz cavities. I have three Decibel products cans, which look the size of regular 150 MHz cans, but have been told they are actually an old 450 MHz all pass-band duplexer. I don't know the model number but they are beige in color and look really old. They will tune very good throughout the 440-470 band, but also work good on 144-174, too. The plunge rod is nearly identical to the old Wacom 2M ham duplexers. Since it is just a pass band cavity, there are two coupling loops, one input, and one output.
Using the same loops, I cut one of the rods down nearly 4 inches, then spliced with a 1 inch copper coupling and soldered together. Now the can tunes a good pass band at 222-225 MHz also. I really wanted to create a hybrid ring 3 cavity duplexer for a new 220 repeater, two cavities on RX and one for TX, band-pass, band- reject, like the Wacom deals with the rod on the side which has a plexiglass looking dielectric that slides in and out in order to determine the position of the notch. I took my existing 220 duplexer (Wacom) loops out and the reject stub also, and tried to duplicate it as closely as possible. So far the results look promising. I am using 3/8" hard drawn copper for the sleeve, and a piece of #10 wire for the inner conductor, and some vinyl tubing to slide in and out to vary the capacitance. I couldn't find any better means of making a capacitor than this, and my first question is, will this be stable in an uncontrolled environment? 90 deg in summer and 40 in winter. Second, I measured the capacitance of the Wacom stubs and get somewhere around 7 pF. I have a bunch of piston type caps that will give this value, plus or minus, but don't know exactly how to incorporate this into the hybrid ring design. I am tired of randomly trying pieces of copper straps for different lengths of coupling loops and wonder if anyone has a proper way to determine coupling loop lengths? Third, the repeater will not be operating in a high RF environment. Would it be more practical to use each can as a notch only (reject) cavity? If so, how in the world do you make coupling loops to work for band reject only? I have tried taking one loop, running it down the cavity for several inches, then directly back up and to ground again. Then taking a tee connector and going across it, but with the tracking generator, my notch is only like 6 dB deep which obviously won't work. Any suggestions or links you can think of to help me build a 220 duplexer out of the parts I have mentioned above? I have a decent shop and can do light precision machine work. Thanks. 73, KC4FWC http://www.w4dex.com/kc4fwc/224480.htm Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
