Yes it does, all sites with more than one transmitter need to have circulators and low pass filters. Just to give you an idea, I got called out to a plant about 5 years ago and they had 3 repeaters on Manufacturing freqs. Spread throughout the plant. Of course they were channels like 462.30, 462.35 and 462.275...now you can think about this and when you mix all 3 of these together along with portables on the 5 meg offset you'll have a lot of mixes on the input, without circulators these mixes will get back into the amplifiers and be amplified and cause all sorts of problems. That's exactly what they had, everything works fine until 2 or more repeaters are up and all of a sudden you have IM on the inputs wiping out the intended input portables. 3 Circulator/Isolators later, everything worked perfectly. It was wonderful as they were letting each dept. order their own equipment so they had 3 vendors pointing at each other, so they called me on a recommendation. After that we had 100% of their business.
Gregg R. Lengling, W9DHI, Retired Administrator http://www.milwaukeehdtv.org K2/100 S#3075 KX1 S# 57 Member: ARRL, RSGB, RCA, WERA and ORC -----Original Message----- From: lcradio2002 [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 03, 2004 11:37 AM To: [email protected] Subject: [Repeater-Builder] Re: Seperate TX / RX antenna questions... Greg, Thanks for the heads up. Just to make sure you know what I am talking about, this is not a true combiner, since each repeater has a seperate TX antenna, they are not combined. Does the circulator/filter setup still apply to TX antennas in the same proximity? Thanks, Tracy --- In [email protected], "Gregg Lengling" <[EMAIL PROTECTED]> wrote: > That is poor engineering practice. On any site with multiple transmitters > you must use a Circulator and Low pass filter to prevent mixing in the > amplifier stages. What you have happening is that the possible IM products > that fall within the passband of the amplifier stages are being amplified > and probably are causing your own interference. > > If you go to any website for a combiner company (TX/RX for example), you > will see that on a TX combiner system you will have an Isolator/Circulator > on the output of each transmitter, then fed to at least one 1/4 wave pass > cavity and in most cases a two 3/4 wave cavities. > > Gregg R. Lengling, W9DHI, Retired > Administrator http://www.milwaukeehdtv.org > K2/100 S#3075 KX1 S# 57 > Member: ARRL, RSGB, RCA, WERA and ORC > > > > -----Original Message----- > From: lcradio2002 [mailto:[EMAIL PROTECTED] > Sent: Monday, August 02, 2004 8:07 PM > To: [email protected] > Subject: [Repeater-Builder] Seperate TX / RX antenna questions... > > Group, > I have 3 UHF repeaters (TKR850) at one site, and one is getting some > inteference. The system has a single, top mounted (60') DB420 > feeding a RX multicoupler (Sinclair with a window filter). From > there it goes to each repeater receiver. On the TX side, each > repeater has it's own antenna, a DB408D (there are two TX antenna at > about the 20' level, antennas are about 6' apart horizontally). I > tried running without any cavities or duplexers, and it worked OK, > but one receiver would get hit and key up. I put a single duplexer > can in the RX path and it helped a lot. > > My question has to do with the type of cavity filter to use. I have > some of the MOT square duplexers lying around (BPBR), and some 8" > diameter TXRX cavities (BP only). In a system like this, which is > normally used? Is it normal to put the cavity on the RX side only, > TX side only, or both sides? > > I have never seen a multicoupler / seperate TX antenna system up > close, so I dont know what is normally done in industry. > > Thanks, > Tracy > > > > > > > Yahoo! Groups Links 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/
