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[Shad Groverland]

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

Sent from my VS995 using Tapatalk

I wish I did but there is no budget for something like that so it is left to me and my troubleshooting skill set. I also wish I had a scanner but access to one left when I left my last company.

[Shad Groverland]

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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In the rack or out of the rack, no improvement.

[Jerome Malsack]

And the building is what construction materials.  Metal frames, wood structure, concrete and glass.   Think about how your wireless and 1/4 wave antenna require a ground plane.  How does the antenna get it's ground connection.  Where does that ground wire run compared with your gear and location.   I have had Radar on navy ships and at airports audible on audio gear. 

[Peter Carpentier]

Shad,

I have experienced this issue a few times in venues that have cellphone transmitters installed on the roof. 

In one case, after pulling my hair out chasing down an induced tone, I found a white plastic disc mounted to the ceiling with a fat piece coax coming out of it.  I disconnected the coax and the noise went away.  Later, we traced the cable back to the roof and discovered a large cell transmitter there.  The hotel engineer stated that it had been installed for an event and left there.  In this case, and a few others, the victims were Meyer powered speakers (Melodies and UPA's).  In another venue in SF my audio vendor wrapped his UPA's (top and back) with what I believe was Black Wrap (the stuff that lighting guys use) and it actually helped!

I could bore you with several other anecdotes, but this all to say that I believe you are correct in your assumption and that the only solution is to shield your equipment.  So, as silly as it sounds, you might try building a "tin foil hat" over your racks to see if that helps.

Cheers.

[Scott Holtzman]

Shad,

I have experienced this issue a few times in venues that have cellphone transmitters installed on the roof. 

In one case, after pulling my hair out chasing down an induced tone, I found a white plastic disc mounted to the ceiling with a fat piece coax coming out of it.  I disconnected the coax and the noise went away.  Later, we traced the cable back to the roof and discovered a large cell transmitter there.  The hotel engineer stated that it had been installed for an event and left there.  In this case, and a few others, the victims were Meyer powered speakers (Melodies and UPA's).  In another venue in SF my audio vendor wrapped his UPA's (top and back) with what I believe was Black Wrap (the stuff that lighting guys use) and it actually helped!

I could bore you with several other anecdotes, but this all to say that I believe you are correct in your assumption and that the only solution is to shield your equipment.  So, as silly as it sounds, you might try building a "tin foil hat" over your racks to see if that helps.

Cheers.

That was a passive repeater you disconnected.  Doubt it had much back channel recovery.

Small point, those are not cell phone transmitters on the roof, they are transceivers.  A cell signal is duplex path.  Not only do you have to talk out to the phone you have to talk back.  In the industry modern integrated cell sites are referred to as RBS's or Radio Base Stations.

[Peter Carpentier]

That was a passive repeater you disconnected.  Doubt it had much back channel recovery.

Small point, those are not cell phone transmitters on the roof, they are transceivers.  A cell signal is duplex path.  Not only do you have to talk out to the phone you have to talk back.  In the industry modern integrated cell sites are referred to as RBS's or Radio Base Stations.

So you're saying I don't have to hold down the send button on my phone whenever I talk?

[Bob Leonard]

If you're holding down a button to talk then you have a transceiver, not a phone.

OP, at a certain point all the ground in the world won't stop the incoming signal from saturating you very sensitive audio hardware. Anything will act as a receiver if the signal is strong enough, and in your case the proximity to the tower is your issue. You can contact the FCC and they will survey the site. If the fault is due to a poor installation of the transmitting device then the owner is obligated to cure the problem. If not you're SOL. You could always look up the meaning of tempest, but that's not a practical solution.

Henry Cohen has the chops to work an issue like this, and I would wonder what his response to my post may be. But he's the guy I would be listening to.

N1BRH

[Scott Holtzman]

If you're holding down a button to talk then you have a transceiver, not a phone.

OP, at a certain point all the ground in the world won't stop the incoming signal from saturating you very sensitive audio hardware. Anything will act as a receiver if the signal is strong enough, and in your case the proximity to the tower is your issue. You can contact the FCC and they will survey the site. If the fault is due to a poor installation of the transmitting device then the owner is obligated to cure the problem. If not you're SOL. You could always look up the meaning of tempest, but that's not a practical solution.

Henry Cohen has the chops to work an issue like this, and I would wonder what his response to my post may be. But he's the guy I would be listening to.

N1BRH

Bob is right, all you need for a functioning receiver is a diode connection.  Even a loose filling can form a diode connection given the right circumstances.

Given an ERP (effective radiated power) of a modern RBS of around 400W per sector that's a significant amount of microwave energy.  It can get into anything.

Ditto on Henry being able to offer the best mitigation advice.

[Henry Cohen]

Ditto on Henry being able to offer the best mitigation advice.

I feel like the genie in the bottle being summoned . . .

Without being able to quantitatively measure the RF spectrum in detail (broadband and with good resolution bandwidth) there's no way of establishing in band and out of band emission levels from either the cellular installation on the roof or, if installed, the in building DAS (distributed antenna system), which would most likely be active, employing one or more bi-directional amplifiers. Only then can a determination be made if the out of band emissions exceed FCC technical rules.

OP - Actually, there's quite a substantial amount of online information dealing with the mitigation of RFI and EMI induced noise in audio circuits (thank you Neil Muncy, Henry Otts, Jim Brown, Bill Whitlock and others), you just have to know the right search terms: "RFI", EMI", "SCIN" "audio shielding and grounding" are but a few. Cell towers are only one source of RFI; there are many.

http://www.audiosystemsgroup.com/publish.htm: Scroll down to the middle of the page to "Hum, Buzz, and RF Interference -- Written for Audio Professionals"

http://www.jensen-transformers.com/application-notes/


Just keep in mind the stronger the RFI and EMI fields, the cost for the mitigation gets expensive very quickly.

[Henry Cohen]

OP, at a certain point all the ground in the world won't stop the incoming signal from saturating you very sensitive audio hardware. Anything will act as a receiver if the signal is strong enough, and in your case the proximity to the tower is your issue.

This.

You can contact the FCC and they will survey the site.

Sigh . . . I remember those days. But we're old. These days, unless you're a public safety entity, the FCC will only respond [eventually, maybe] if you have performed traceable measurements and present the data to the Enforcement Bureau. And best to use telecommunications counsel who know the folks there.

You could always look up the meaning of tempest, but that's not a practical solution.

"Tempest"? How 1990's, early 2000's. Now the buzz term is "SCIF"

[ProSoundWeb Community]