In NZ we used to have VHF repeater services on 101-108 MHz (AM) and there were quite a number of surplus cavity filters floating around from the old TX combiners and RX multicouplers. If you are in need of something email me off list.
Cheers _________________________________________________________________ Gareth Bennett This e-mail is confidential, if you received this message in error, or you are not the intended recipient, please return it to the sender and destroy any copies. Thank you. ----- Original Message ----- From: skipp025 To: Repeater-Builder@yahoogroups.com Sent: Friday, November 23, 2007 8:47 AM 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: Repeater-Builder@yahoogroups.com > [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 > Sent: Thursday, November 22, 2007 2:07 PM > To: Repeater-Builder@yahoogroups.com > 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/ > > >
