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[Shad Groverland]

The question was how do you know the equipment is getting the noise with nothing connected to it?
How do you hear the noise?

With nothing connected on the inputs, if it is a CD player, RF receiver or console, I plug into the headphone jack and can hear the interference above the normal noise floor. If it is an amp, I have connected speakers and can hear it with the gain turned only 1/4 of the way up and that is how I have to run the amps. With input signal connected, amps at half or full gain has so much interference it is nearly as loud as the minister speaking. 

[Cailen Waddell]

Is all the equipment in a common rack?  If so, the rack rails are grounding the gear together.


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[Kevin Maxwell]

I was dealing with a church that wasn’t far from an AM transmitter and they had a problem for years with interference. For other reasons we changed a bunch of their gear including adding a digital console. I never experienced the problem they described and it seemed that all was ok with the new gear. Then the problem started again and I started troubleshooting it. I found an outlet that was wired improperly and when it was used for a keyboard the problem showed up I also found that the wire had a nick in it where it was missing the insulation only after rewiring it and that nicked place was now touching ground. It immediately and dramatically popped the breaker. I thought that I had done something wrong and then found the problem. After fixing that the radio station (to the best of my knowledge) is no longer interfering. They haven’t called me back in for that and I have been back there for other things.

You need to also check all of the wiring. It might meter ok depending on how you are metering it, but there might be a loose connection in the building wiring that is causing or contributing to this issue. Do you know what a NCVT is? Get one and also use it to test for bootleg grounds. They are cheap.
http://www.kleintools.com/catalog/electrical-testers/non-contact-voltage-tester
http://www.homedepot.com/s/ncvt?NCNI-5

[Kevin Maxwell]

Also if you have a battery powered headphone amp (like the Shure FP12) plug you headphones into it and set it to the most sensitive input setting and bring the volume all the way up. Now walk around with it waving it over things using like a metal detector with the headphones on. If there is noise in the air this method might pick it up. You will probably need to get right up to where any cabling or power is run. It worked that way for me when I was trying to figure out where the noise was getting into the audio truck for a video shoot of a concert. It turned out to be everywhere that the lighting people had laid there VARILIGHT cabling on top of the audio cable and it was specifically everywhere one of their cable extension connectors were.

[Shad Groverland]

Is all the equipment in a common rack?  If so, the rack rails are grounding the gear together.


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No, different racks in two different locations and each have the problem independent of each other.

[Scott Holtzman]

One thing to keep in mind with spread spectrum equipment and spectrum analyzers is you have no distinct carrier.  The spreading algorithm distributes the energy across the occupied bandwidth.  As traffic on the site increases more power is used so you have more energy across random points in the spectrum assigned to each sector (for all intents and purposes each sector is a different system)  millimeter wave microwave energy gets into everything and is very difficultult to mitigate. 

Do you have the budget to bring in consultants?  Two of the best in the world work out of Boca Raton

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[Cailen Waddell]

No, different racks in two different locations and each have the problem independent of each other.

Ok - when testing was the gear removed from the rack? Otherwise it's chassis ground is still shared with other collocates equipment.  Tho - this does sound unlikely given the two rack issue.


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[Henry Cohen]

One thing to keep in mind with spread spectrum equipment and spectrum analyzers is you have no distinct carrier.  The spreading algorithm distributes the energy across the occupied bandwidth.  As traffic on the site increases more power is used so you have more energy across random points in the spectrum assigned to each sector (for all intents and purposes each sector is a different system)  millimeter wave microwave energy gets into everything and is very difficultult to mitigate.

I don't see the relevancy of this: None of the mobile phone technologies (CDMA, GSM, HSPA, PCS, AWS, LTE, etc.) in use are spread spectrum schemes.

[Scott Holtzman]

I don't see the relevancy of this: None of the mobile phone technologies (CDMA, GSM, HSPA, PCS, AWS, LTE, etc.) in use are spread spectrum schemes.

Since GSM uses CDMA tech today e can lump it all together.

CDMA is a spread spectrum technology with a pseudo random sequence.  The PN codes are what the phones use to seed the coder.

Thhe more relevant point for the discussion was the change of the output based on capacity.  You dont see carriers, side band energy or and of the spectral characteristics of a carrier based system.  This presents a challenge for interference mitigation.

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[Dave Garoutte]

It seems to me any time you're that close to a high powered transmitter, you're going to pick up something.  How it manifests itself is the question.  Even the AC in the building could be picking up something.

Shielding, good!

[ProSoundWeb Community]