The Radio Information Board

Hello To All, I have local Red Cross office that called me with question concerning interference to a newly installed low band mobil in a desktop configuration. They say that of the 10 freqs that are programmed into the radio the problem is only occurring on ch 1 and no others. The freqs are all simplex,and carrier squelch. They say that one of the computers in the room that is housing the radio is the culprit but cannot do without the computer. OH yea...the problem is that ch 1 unsquleches and emits a horrible hiss and noise and they are unable to quiet it thru normal squelch adjustment. The interesting thing that they reported is that when the coaxial cable is removed from the rear of the radio and ONLY the center conductor inserted into the so239 on the back of the radio and no full insertion to the point of being able to screw the outer half/shielded portion of the pl 259 connector to the radio chassis the noise goes away. They have tried different ant and coax,different power supply,and different 110v outlet so as to remove the radio form the same circut as the noisy computer still no luck..
What would cause the noise to only be present in this condition? Any advice would be greatly appreciated,
Thanks in Advance............DEL

Looks like you already tried the obvious. How about grounding the computer to a good ground, like a cold water pipe or ideally a separate ground rod. Also try turning off all the monitors to isolate them as the noise makers. Might also try replacing the offending computer's power supply. Some of those cheap Chinese made switching power supply units make huge amounts of RF noise.

I just did a search on this website of this problem and found lots of info.I will be going out there today and do some first hand checking.
Thanks for the reply

Let us know what you find. Peter

Aside from the programmable squelch option,there is also an internal sq pot under the top cover that may not be adjusted for tight squench. It is silk screened sq on the board,turn it fully counter clockwise.
mod

Another thing to look at is the monitor. Unplug it from power, and the video connection at the computer.

It sounds to me like you have a power ground loop. One other diagnostic step woud be to run the radio on a battery. From what's been said, I'm betting that the problem is related to a ground loop and the feedline is a part of it.