VK4ZXI

Homebrew cavity resonator/duplexer for 2m repeater There has been some interest in the club establishing another 2m repeater, but lacked a duplexer. A couple of old cavity resonators were discovered in the back shed. We were able to tune these very quickly and easily using the new Chinese KC901H network analyser (more about that in another post). Why and how they work: an antenna in a box! Up to that point I had heard of cavity resonators but had little idea of how they worked or how they were made. Similarly, so was my knowledge of repeater. However, as I started to learn about them, I became quite intrigued with the technical finesse of being able to transmit and receive with the same antenna simultaneously, albeit on different frequencies. Further, as desirable repeater sites are restricted in number, many repeaters share the same site, again on different frequencies and bands. The solution to the repeater problems is in using very selective band-pass and/or notch filters, wh