big radio problems

[andrew Hill]

Here's the deal.....
I am doing a re-vamp on a smaller system in a youth room at a church. The system consists of a mackie 16-04, and a couple early model Jbl Eons. The snake is 150' long and runs under a suspended concrete floor, and as far as I know does not come in contact with any utilities along the way. It terminates at a 24 channel patch bay behind the stage. The stage has four floor boxes that each have eight sends to the patch bay. We have not been able to use the boxes, because doing so results in terrible radio on almost all channels. I found some wiring inconsistensies in the snake ends and the boxes, so I re-wired everthing to the standard (sheild on pin one). It helped some, but I still can't use the boxes. If I plug an xlr straight into the patch bay, some of the channels have radio and some don't. I have another snake that I have been using as a temp that doesn't create the radio problem, but It doesn't alow me to use the floor boxes. The problem is BAD, and I have exhausted my limited knowledge of how to rid a system of RFI. Please HELP!
Thanks,
Andrew

[cmchamp]

Andrew:
Sorry no one has posted. I'm dealing with the same thing at a church I'm installing at. They are 4 blocks from a 10kwatt AM station.
How long is the substitute snake? I've been told that Mackie's have trouble with their mic pre-amps and lengths of cable over 75'.
Here are a few things to try.
1: don't use phantom power.
2: has there been any water damage to the boxes and cable runs in the floor? Sounds like the shielding has been compromised.
3: can you pull some new cable through the floor with the stage boxes?
4: conduit? any in the floor?
5: Isolation transformers?

It's been since February, so you probably had someone come in and help out.