Tony, If the source of interference is the third harmonic from the 152 MHz station then there is nothing that you can do at your end to fix it! You'll need to concentrate on the offending VHF station. Is there any components in the receive path of your UHF station such as a preamp or receiver multi-coupler that could be causing a harmonic response from the fundamental of the suspected VHF station?
I would also want to verify if the suspect VHF station was actually putting out the harmonic by driving to that site and checking the field strength and then to correlate that signal against that stations fundamental (VHF) frequency. There could be any number of reasons or sources for the interfering signal but you first need to know without a question if it's actually radiating from the VHF site or if it's a product of something in your own transmission path or local site as a starting point. Good luck! Bill, WA8WG ----- Original Message ----- From: "Tony KT9AC" <[email protected]> To: <[email protected]> Sent: Tuesday, September 29, 2009 8:14 PM Subject: [Repeater-Builder] Need help with harmonic overload > Hey everyone, > Working on a MSF5000 repeater with a 457 receiver getting overload from > a nearby 152 data transmitter (almost exact 3rd harmonic). The two > towers are about 10 miles apart and of course line-of-sight. > > I seem to recall that UHF duplexers only have a useful range of 300-600 > Mhz so that might explain why the 152 signal comes through so strong > (monitoring on the receive port of the Moto T4084 duplexer). The 457 > "harmonic" signal is also very splattery so I'm not entirely convinced > its just a mathematical problem, but I'll address that later... > > What would be the best course to eliminate this signal? I can't notch > out the harmonic since it falls almost exactly across our receiver, so > going after the 152 signal makes sense. Can I add a stub tuned 1/4 wave > with a T between the duplexer and receiver? Do I need something stronger > as a notch filer, or some sort of band-pass? > > Thanks in advance for any help. > > Tony > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
