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[John Eickenroth]

We have recently moved our church to a new location which happens to have 4 big radio towers near by. The single from the radio is bleeding into different lines in our PA. Has any one ever had to deal with this problem and is there a way to fix it?

We have a 16 Chanel mackie mixer (analog). We have run a 16 Chanel snake to the stage. The snake runs up the rear wall overhead to the sound booth douw the wall to the board. Iam using crown amps and Peavy impulse 12" speaker with 18" carvine bass bins.

Any help will bw greatly appreciated

Thank you All

[Brad Weber]

John Eickenroth wrote on Sun, 25 November 2007 14:21

We have recently moved our church to a new location which happens to have 4 big radio towers near by. The single from the radio is bleeding into different lines in our PA. Has any one ever had to deal with this problem and is there a way to fix it? We have a 16 Chanel mackie mixer (analog).

Unfortunately, many of the Mackie mixers are well known for RFI problems on the inputs.  There are some modifications that can be made to the inputs that might help, you can contact Mackie on those, but it may not resolve the issue.

Quote:

The snake runs up the rear wall overhead to the sound booth douw the wall to the board.

What is the snake?  Poorly shielded cable run without conduit certainly won't help the situation.  But I would initially focus on the console inputs.

[Bruce Burke]

I had a similar problem. The quality of mic cable used made a significant difference in the amount of interference I would receive.

-Bruce

[Andrew Welker]

I'm assuming it is AM, since that is typically what tends to get into the signal path and get demodulated in the electronics. Your best bet is to put some sort of RFI filter in front of the mixer inputs.  Shure makes one that is XLR in and out and also passes phantom power.  The part number is A15RF.  Your local Shure dealer can get them for you.  Also, you will probably want to put one in front of each microphone that is a condenser microphone, as the electronics in the microphone will demodulate the signal and it will show up as audio in the microphone line.

Andrew

[Jerrybosun]

Start with finding out what part of the pa is picking up the noise. If you plug a mic directly into the board and listen on headphones with the channel soloed is the station there?  If not turn the mains up with all the channels down, then close mic up? then each channel.  Please let us know what happened. we are always interested!

[Elllery J. Durgin]

John,

First off here is a great article about RF interference.
http://www.prosoundweb.com/install/synaudcon/tt25_2.php

As Jerrybosun has pointed out. The first thing to do is locate the source. You said that the radio is bleeding thru on multiable channels. This is the most common point where http://en.wikipedia.org/wiki/Radio_frequency_interferenceRFI gets into sound systems, also one of the hardest to solve.

Here are a few thing's to try.

1. Disconnect all microphone cables from the snake. Does the interference go away? If so plug each cable back in one by one. until you find the bad cable.

2. Check the connector on every cable and ensure the shield (the bare wire ) is connected to pin 1 (See fig 1)
 

Fig 1

3. Using a standard microphone cable, plug into one channel of the mixer at a time. Does the problem still occur?

4. Check for a proper earth ground on the mixer. is the center pin in good shape?
http://publib.boulder.ibm.com/infocenter/systems/scope/hw/in dex.jsp?topic=/iphbf/ac.htm

5. If you have a different mixer. Try it. This will help rule out mixer problems.


How old is your snake?

[Bruce Burke]

We had a 24*8 that was suseptible to RFI. It got worse the further away from channel one you were, which seems to indicate something about how the boards were grounded internally.

The type of mic cable used made a huge difference too, as others have pointed out.

The 24*8 had a screw so that you could earth ground it, but in the location we had our mixer, it wasn't possible. You might look into doing that. I was at least able to keep it enough under control with being careful about what cables I used so that the congregation couldn't hear it.

The fix gets more severe from there.

-Bruce

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