Yes and no... for the most part they will work just fine as 3/4 wave cavities. The fly in your soup is the loops or probe lengths.
While 150Mhz loops will actually work at 450MHz (not very well) there is a best practical loop target size. The best way to use your 150MHz band pass cavity at 450MHz is to tell me/us which brand/type/size it is and we'll give you the loop size for the 450MHz version. Shorten your loops or better yet make new loops and you'd be ready to rock and roll if everything plays as expected. skipp www.radiowrench.com/sonic > "Kevin & Natalia" <[EMAIL PROTECTED]> wrote: > Are you then saying that some of my cavities I > have for 150Mhz, I can use without any mods for > around 450Mhz. If this is correct, I would be > very happy, as I can use them, instead of > them sitting around waiting to be used. > Kev. > > ----- Original Message ----- > From: "skipp025" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Friday, June 24, 2005 11:41 AM > Subject: [Repeater-Builder] Re: how broad are cavities? > > > > 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 > > > > > > > > > > > > > > > > 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/
