Use at your own risk.
This is my duplexer conversion page. I tried to show every detail with pictures taken by John (wd7f). Special thanks to Jacques ve2azx. He wrote Theory and Testing of Duplexers. Jacques answered many questions and helped solve many stumbling blocks. I cannot thank him enough. This project isn't for the faint hearted. We spent many hours working on this conversion and it requires access to specialized equipment. You have to be able to transmit your pass frequency and scroll through your reject frequency into the duplexer while watching the spectrum analyzer. There are 3 adjustments, the pass (screw stud), reject (loops) and the capacitor (reverses the pass/reject and also affects both). Some tips that I have found are the following: adjust "on site" in the rack, use a non-metallic screw driver for the capacitor, Have your low loss cables cut properly (we used a vector volt meter), between the duplexers the cable cut was 28.5 degrees of the pass frequency, "OUT" of the duplexers to the "T" was 143 degrees, and to the "IN" connectors of the duplexers we cut the cables at 50 ohms for the particular frequency. I found that when the duplexers were "paired up" it affected the adjustments greatly. You have to be patient as I spent a whole weekend just on the adjustments with my experimentation. One tip in particular is this, if have good isolation and your pass and reject look good but the insertion loss is high, back out the adjustment screw for the pass and turn the capacitor to the left for the receive, or to the right for the transmit. I found I could lower the insertion loss but then I ran out of capacitor adjustment. You will have to experiment with the loops length in the middle of the loops. I tried lengthening one set by soldering some copper flashing 1/4" X 1/4" to the outer edge (away from the center where the loops come together in the duplexer) and the insertion loss went up. So you may have to slightly remove some material in this area. I would start with 1/16" per loop and see what happens to your insertion loss. I ended up with 224.740 72 dB and 2.25 insertion loss, 223.140 78 dB and 3.2 insertion loss. I found 2 duplexers on TX and RX with this isolation worked for my situation with no de-sense of the receiver with the transmitter operating. This is also with my Advanced Receiver Research preamp. I plan on another experiment with the loops and another set of cans soon. I will keep you posted. de k7iou
The finished duplexer pack all cabled and ready to install. The transmit pair had 51 db isolation, insertion loss was .075 db, and the receive pair had 58 db isolation.
Here are the formula's we used for cutting the cables. Courtesy of Jacques ve2azx Here are TX duplexers on the spectrum analyzer and the RX they are showing 72 and 78 dB isolation. Sorry for the bad pictures.
More to follow de k7iou.