Trying to get a notch cavity for 104 MHz that will pass 900 MHz might be a problem.
Also using coax as a notch one has to make sure it does not do same at 900 MHz. A 1/4 wave at 104 MHz has lots of notches at the high frequencies, but I would give it a try. A bandpass at 900 would probably be an easier choice, but think this has been tried. 73, ron, n9ee/r >From: skipp025 <[EMAIL PROTECTED]> >Date: 2007/11/22 Thu PM 01:47:43 CST >To: [email protected] >Subject: [Repeater-Builder] Re: Receiver overload > >As a generic rule of thumb... the larger the cavity >diameter the higher the internal Q. If nothing else >don't forget you can use low band cavities in the 3/4 >wave mode. Trying to find an min 8 to 15 inch diameter >notch cavity on 104 MHz might be a bit of fun for the >average Joe. > >As an example... cavities for broadcast work are often >the size of the average home shower stall. And they get >real warm in operation. Since you're not using it in >the BC transmitter pipe (hard-line), you don't need to >worry about the unwieldy physical size bottles. But you >do need as High-Q cavity as you can find. > >One other last though... you might be able to make enough >of a notch function using sections of 1-5/8 inch hard line >as in the same example we see with folks making low-band >duplexers. > >cheers, >skipp > >> "David Epley" <[EMAIL PROTECTED]> wrote: >> >> I am looking for a cavity now >> >> >> >> _____ >> >> From: [email protected] >> [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 >> Sent: Thursday, November 22, 2007 2:07 PM >> To: [email protected] >> Subject: [Repeater-Builder] Re: Receiver overload >> >> >> >> In this case... I would expect the band-pass cavity option >> to be a popcorn fart. See my post about the High-Q notch >> cavity (with the dc return probe) and the attenuator, which >> should help if the problem is source to the RF coming in >> the coax port is the sole source. >> s. >> >> > "David Epley" <depley@> wrote: >> > >> > I just tried a pair of Celwave 8 inch band pass cavities with no >> noticeable >> > improvement. >> > >> > >> > >> > >> > >> > David N9CZV >> > >> > >> > >> > _____ >> > >> > From: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> >> yahoogroups.com >> > [mailto:Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> >> yahoogroups.com] On Behalf Of Jim Brown >> > Sent: Thursday, November 22, 2007 6:13 AM >> > To: Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> >> yahoogroups.com >> > Subject: Re: [Repeater-Builder] Receiver overload >> > >> > >> > >> > David, try using one or two band pass only cavaties in >> > the receive side instead of the BpBr type. The BpBr >> > filters often do not discriminate against signals far >> > off the pass frequency, and you may not be getting >> > enough rejection out of your input cavities. >> > >> > 73 - Jim W5ZIT >> > >> > --- David Epley <[EMAIL PROTECTED] <mailto:depley%40starband.net> >> net> wrote: >> > >> > > I have a repeater receiver overload problem I am >> > > trying to cure. The >> > > repeater is a 900mhz 927.7125/902.7125. There is an >> > > FM broadcast station 100 >> > > yards away 104.9mhz. The repeater works fine at >> > > another site. My transmitter >> > > is a Motorola Purc 5000 running 75 watts the >> > > receiver is a converted maxtrac >> > > 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I >> > > have 10 to 12 db >> > > degradation when plugged into 3 different antennas >> > > on the tower. When I use >> > > a 900mhz dish antenna pointed away from broadcast >> > > tower I only have 3 db >> > > degradation. I have tried 3 different maxtrac >> > > receivers, added 2 more BpBr >> > > cavities in the receiver side and used 3 pole >> > > filters in the receivers with >> > > no improvement. Today I looked at the signal level >> > > getting to the receiver >> > > at 104.9. To my surprise I was getting -8 dbm at the >> > > receiver. I believe >> > > this level is overloading the front end of my >> > > repeater. I was wondering if a >> > > stub cut for the broadcast frequency would work. Any >> > > thoughts would be >> > > greatly appreciated. >> > > >> > > >> > > >> > > >> > > >> > > David Epley, N9CZV >> > > >> > > Winchester, Indiana >> > > >> > > >> > >> > __________________________________________________________ >> > Be a better pen pal. >> > Text or chat with friends inside Yahoo! Mail. See how. >http://overview. >> > <http://overview. <http://overview.mail.yahoo.com/> mail.yahoo.com/> >> mail.yahoo.com/ >> > >> > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
