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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Wireless and Communications => Topic started by: Elliot Carroll on November 15, 2016, 06:24:23 pm

Title: Hey Smart Guys, what are these?
Post by: Elliot Carroll on November 15, 2016, 06:24:23 pm
Myself and the lovely Mike Kahrs are doing Frequency Coordination for two different parts of a large show here in the Venetian and Sands Expo in Las Vegas.  This morning, on the day of the first show, one of my L3's was getting slammed from some kind of external source, afterwards Mike and I tracked it down.

(http://C:\Users\Elliot\Desktop\RF pic.JPG)

We found what looked like to be Cell Repeaters that belonged to AT&T.  There was 6 of them mounted on the wall in a banquet storage room in the hallway between Hall C and Venetian J Ballroom.  They looked like oversized computer towers.  The odd thing was it was a very, very tight peak right at 691.000mhz.  It looked exactly like an RF Mic on the scanners.

Ideas?


Title: Re: Hey Smart Guys, what are these?
Post by: Henry Cohen on November 15, 2016, 09:40:05 pm
Myself and the lovely Mike Kahrs are doing Frequency Coordination for two different parts of a large show here in the Venetian and Sands Expo in Las Vegas.  This morning, on the day of the first show, one of my L3's was getting slammed from some kind of external source, afterwards Mike and I tracked it down.

(http://C:\Users\Elliot\Desktop\RF pic.JPG)

We found what looked like to be Cell Repeaters that belonged to AT&T.  There was 6 of them mounted on the wall in a banquet storage room in the hallway between Hall C and Venetian J Ballroom.  They looked like oversized computer towers.  The odd thing was it was a very, very tight peak right at 691.000mhz.  It looked exactly like an RF Mic on the scanners.

Those are actual micro-cell transceivers, likely with a fiber-optic backhaul. Each box (I believe those are Alcatel-Lucent) is a different paired frequency block for which AT&T is licensed in that market. The one generating the 691MHz is probably one of the 700MHz LTE units emitting an IM product whereby one of the 700MHz channels is a contributor.

I (and Peter) have several times run across DAS installations where the techs installing the equipment turn the BDA gains up to "11", do a simple pass/fail coverage test, rather than actually measuring field strength levels and adjusting for a median level. This of course results in high RF noise floors, IMD and general spurious emissions. AT&T is technically committing a rules violation with that strong out of band signal.
Title: Re: Hey Smart Guys, what are these?
Post by: Elliot Carroll on November 16, 2016, 10:54:46 am
Those are actual micro-cell transceivers, likely with a fiber-optic backhaul. Each box (I believe those are Alcatel-Lucent) is a different paired frequency block for which AT&T is licensed in that market. The one generating the 691MHz is probably one of the 700MHz LTE units emitting an IM product whereby one of the 700MHz channels is a contributor.

I (and Peter) have several times run across DAS installations where the techs installing the equipment turn the BDA gains up to "11", do a simple pass/fail coverage test, rather than actually measuring field strength levels and adjusting for a median level. This of course results in high RF noise floors, IMD and general spurious emissions. AT&T is technically committing a rules violation with that strong out of band signal.

Thanks for the information Henry, will note to look for these in the future.
Title: Re: Hey Smart Guys, what are these?
Post by: Mike Kahrs on November 16, 2016, 06:11:24 pm
Very interesting, Harry.  Thanks.  One more thing to look out for when lurking around convention centers, and some interesting reading re: DAS.

Mike
Title: Re: Hey Smart Guys, what are these?
Post by: Scott Helmke on November 18, 2016, 10:01:00 am
AT&T is technically committing a rules violation with that strong out of band signal.

Would there be any useful way to approach that violation, as a frequency coordinator or as a licensed wireless mic user?
Title: Re: Hey Smart Guys, what are these?
Post by: Henry Cohen on November 18, 2016, 12:01:04 pm
Would there be any useful way to approach that violation, as a frequency coordinator or as a licensed wireless mic user?

Depends on how you wish to define "useful".
"Useful" as in getting it corrected before the end of your event? Hardly.
"Useful" as in merely documenting the issue with the FCC and AT&T for posterity? Sure; file a complaint with the FCC, cc AT&T (there should have been a site number and telephone number on the door to that room) and include a video of the spectrum analyzer screen.

Then again, you could always look for the electrical service breaker  ::)