The shame about the dumpster part of your post. A 1/4 wave cavity at 150MHz makes a 3/4 wave cavity at 450MHz skipp
> Don Pomplun <[EMAIL PROTECTED]> wrote: > Thanks for the insight, Paul. > The fact that they are spec'd by fairly wide ranges was the info I was > hoping for. I called a friend today whose system switched from the 150 > band to a 400 MHz trunked system a few years ago to see if they had any of > the old cavities laying around. He said that they had just finished > cleaning house last week and all the old junk went to the dumpster, but he > would do some diving to see what was still there. > Regards, > Don > > At 12:03 PM 6/22/2005 -0400, you wrote: > >Don, > > > > > 1. Cavities are roughly tuned by their > > > physical dimensions, and then tweaked by rods, plates, > > > etc., eh? > > > >The length of the cavity (more importantly the inner > >conductor of the cavity) sets the frequency. Usually > >cavities are designed to cover a RANGE of frequencies... > >the tuning rod coming out the top adjusts the length of the > >center conductor inside the cavity. The tuning range > >varies depending on manufacturer and model... some typical > >ranges are 136-150, 150-174, 136-174... and many others. > > > >You might want to check some of the articles referenced on > >the following page for more on cavity and duplexer theory: > > > >http://www.repeater-builder.com/rbtip/ant-sys-index.html > > > >There is a section on Cavities, Duplexers, etc. part way > >down that page. > > > > > 3. How awful a compromise would it be to use available > > > cavities from a 2 meter system at railroad frequencies > > > (160-161 MHz) ? > > > >If the cavities will tune that high, they probably work just > >fine. If the are now on the 2 meter band (below 148 MHz) > >they may or may not tune at 160 MHz... it depends on > >whether the center conductor can be adjusted that far by > >means of the tuning rod. > > > >If you are actually referring to a duplexer (several > >interconnected cavities to allow use of a single antenna > >for transmitting and receiving) there may be other factors > >to consider. The cavities themselves may tune where you > >want them, but the length of the coaxial cables > >interconnecting the cavities may need to be optimized for > >that frequency to get best performance. > > > >The cavities may have more than one adjustment... if they > >are bandpass-bandreject cavities, there will be one > >adjustment for the length of the center conductor (usually > >a big knob / tuning rod) and another adjustment of some > >sort to set the frequency of the notch relative to the pass > >frequency. > > > >If you can tell us what specific cavities (or duplexer) you > >are looking at, some of us can probably provide more > >specific information. > > > >Paul Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
