Low-cost duplexer for 6m, 2m or 70cm I am proposing a conceptual design for a low-cost, home-made duplexer for 6m, 2m, or 70 cm. I have not built one to this design but it combines ideas from duplexers I have made or from commercial duplexers. It is worth reading this post in conjunction with my other posts on cavity filters and duplexers; just search the terms. I have written a guide to how duplexers work and have a list of resources on the building and testing of them. https://vk4zxi.blogspot.com/2018/05/the-black-art-of-duplexers-demystifying.html General arrangement The basic design of a single cavity filter is a large diameter aluminium pipe for the cavity and a 1/3 diameter aluminium pipe welded to a top plate. The coupling is mounted on the same plate. The other end of the large pipe is held to another plate by bolts for access. A capacitive hat on a threaded rod is mounted on the bottom plate to tune the cavity. The main pipe is as large as possible to increase the Q of th...
