Actually, the comment below isn't quite true. The Q2220E is a "Res-Lok" duplexer, but there are no machined coupling ports between the cavities. I just took the loops out of one to confirm.
The coupling between the cavities is a function of the pickup loop inside the cavity, and the coax between them. However, in the C2034 type Res-Lok combiners, there ARE coupling ports machined between the bandpass section cavities (confirmed that too). Of interesting note on the Q2220E, the docs from Sincliar show two different harnesses available, presumably one for high split, and one for low. I have two Q2220E's here, one factory 143/148 and the other 152/157. They both have the same harness on them (320mm inter-cavity of RG400), and the pickup loops are the same size too (110mm). If you run the numbers for 320mm and a velocity factor of 0.695, you get a center frequency for the harness of 163MHz. If you wanted to optimize the tuning for the best response in the ham band, you may want to consider re-building the harness and changing the inter-cavity lengths to 355mm. I wouldn't change the lengths of the pickup loops as that is going to significantly change the response. Also note, the Q2220E makes a good candidate to modify for 220MHz... just ask Dave Cameron... http://www.irlp.net/duplexer Cheers! Lee --- In [email protected], "Eric Lemmon" <wb6...@...> wrote: > Part of the problem is that the Q2220E > duplexer uses the "Res-Lok" design, wherein the coupling between cavities of > each pair is via a machined port between them, rather than a cabled coupling > loop that can be adjusted.
