At 10:15 PM 03/23/08, you wrote: >Hi group, > >I seem to be having an RF Problem with a new Icom FR4000 Repeater. The >repeater is letting out a hissing noise when I listen to it on a HT or >my mobile radio. The hissing noise sounds more like a squelch that is >opened up. When I get about 300 feet from the repeater the noise is >gone. It does not key the transmiter. This is why I am puzzled. The >only way I have found to get arround it is turn my squelch way up on my >HT to remove the noise. When I key up my HT the noise drops out while >the repeater is transmitting. The repeater and repeater tower is at my >home. If it was several miles out of town I would not be emailing you. >I have mounted it in a metal case, grounded the repeater by the >grounding screw, grounded the coax by twisting copper around the coax >sheild, grounded the repeater cabinet. I first thought that the problem >was from the duplexers. Not so, I took the duplexers out of line and >still noise. The only way to remove the noise is to turn off the >repeater. Something I don't won't to do. Any thoughts ???
You are hearing leakage from the transmitter exciter oscillator. In that radio the transmitter oscillator runs full time (for stability) and the following stages are keyed. This is why the problem goes away when you are 300 feet from the cabinet. In most situations the repeater is at a site fat from the users and it's not a problem. I have no experience with late model Icom repeaters so I have no answer for you. Is it a synthesized repeater? Do you have the programming software? If so, the trick that is used on the Motorola MTR2000 may help. See <http://www.repeater-builder.com/motorola/mtr2k/mtr-2000-idle-freq.html> This trick depends on Icom having engineering staff that are aware of this problem and added that feature to the repeater and the software. The similar repeaters made by Kenwood have this feature. They call it the "standby frequency". Mike WA6IOLQ
