I have recently aquired a functional high-split (148-174) Sinclair Q2220E. Since it does not have enough isolation for my 100W VHF repeater, and I already have a good working Q202 on there now, I am planning to convert this over to a Q2221E for 220Mhz.
I am pretty aware of how duplexers work and the coupling harness and 1/4 wave characteristics, so my questions are very specific. I have a Q3330C (compact UHF 6 cavity) and the Q202 that I have looked at for comparing loops and such. I have already determined how I have to reduce the length of the interconnecting harness with the velocity factor and such. The only questions I have are: 1) The coupling loop (with the connector and the variable capactior) on the Q2220E is obviously sized for 148-174. How should the dimensions be changed to work to 220? The reason I am confused is the UHF is the same length, but not as spread open. and made from wider copper stock. The Q202 is much more spread open and larger. What is the electrical/RF characteristics of this loop supposed to be? 2) I know I have to cut down the hollow rod support and the finger stock on the internals of the duplexer to accomodate the 1/4 wave resonance inside for 220. No problem. But, does the depth of the cavity matter? Do I have to shorten the casing as well? I know in the past when I removed the bottom of the large Q202 cans, the bottom being in place or not had little effect on the tuning. If I left the casing alone, would I still be able to tune it to 220? Thanks for your insight. Dave Cameron VE7LTD
