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Author Topic: Wireless 60hz?!  (Read 3235 times)

Benjamin Krumholz

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Wireless 60hz?!
« on: May 04, 2016, 08:25:20 pm »

In the Mayflower hotel in DC, grand Ballroom.. 2 X BTR( A2 and C4)and 12 channels of UHFR.. (H4 and J5) Tested and checked fine... About an hour later the A1, started to complain about a pile of noise on he RF channels and on the Wireless BTR... Chase my tail for about half hour... And located the issue down to a particular part of the ballroom...
So the wireless mics are clean on stage and in other parts of the room, but when I walk down one corridor there appears a 60hz cycle on ALL RF channels.. Now if I stand down the "noisy"corridor and I rotate the handheld or belt pack sideways the noise goes away... Have I created a humbucker somewhere? Happens with all 12 UHFR channels .. And also happens with the TR825 packs... Changed my whole powers scheme around and no change...
So I am living with it.. The RF is crystal clear in all the other parts of the room. Strange... Some iR listen systems operating in the room but I asked him to shut down while I was trouble shooting... Still scratching my head a bit.
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Ike Zimbel

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Re: Wireless 60hz?!
« Reply #1 on: May 04, 2016, 09:00:58 pm »

In the Mayflower hotel in DC, grand Ballroom.. 2 X BTR( A2 and C4)and 12 channels of UHFR.. (H4 and J5) Tested and checked fine... About an hour later the A1, started to complain about a pile of noise on he RF channels and on the Wireless BTR... Chase my tail for about half hour... And located the issue down to a particular part of the ballroom...
So the wireless mics are clean on stage and in other parts of the room, but when I walk down one corridor there appears a 60hz cycle on ALL RF channels.. Now if I stand down the "noisy"corridor and I rotate the handheld or belt pack sideways the noise goes away... Have I created a humbucker somewhere? Happens with all 12 UHFR channels .. And also happens with the TR825 packs... Changed my whole powers scheme around and no change...
So I am living with it.. The RF is crystal clear in all the other parts of the room. Strange... Some iR listen systems operating in the room but I asked him to shut down while I was trouble shooting... Still scratching my head a bit.
It sounds like there is a pretty serious 60Hz field being radiated there. I bet if you went down there with a wired mic you would get it too, although how it is getting across all of your RF channels is a bit mystifying. Are you using one antenna distribution for the UHF-R and the BTR systems?
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brian maddox

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Re: Wireless 60hz?!
« Reply #2 on: May 04, 2016, 09:09:20 pm »

In the Mayflower hotel in DC, grand Ballroom.. 2 X BTR( A2 and C4)and 12 channels of UHFR.. (H4 and J5) Tested and checked fine... About an hour later the A1, started to complain about a pile of noise on he RF channels and on the Wireless BTR... Chase my tail for about half hour... And located the issue down to a particular part of the ballroom...
So the wireless mics are clean on stage and in other parts of the room, but when I walk down one corridor there appears a 60hz cycle on ALL RF channels.. Now if I stand down the "noisy"corridor and I rotate the handheld or belt pack sideways the noise goes away... Have I created a humbucker somewhere? Happens with all 12 UHFR channels .. And also happens with the TR825 packs... Changed my whole powers scheme around and no change...
So I am living with it.. The RF is crystal clear in all the other parts of the room. Strange... Some iR listen systems operating in the room but I asked him to shut down while I was trouble shooting... Still scratching my head a bit.

My wild ass guess is maybe a Metro transformer under the hotel. The train runs basically right by/under the hotel.
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Jordan Wolf

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Re: Wireless 60hz?!
« Reply #3 on: May 04, 2016, 09:36:42 pm »

Any fluorescent lights nearby? LED walls?


- Jordan Wolf
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Benjamin Krumholz

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Re: Wireless 60hz?!
« Reply #4 on: May 04, 2016, 09:45:33 pm »

Any fluorescent lights nearby? LED walls?


- Jordan Wolf

Its a VERY old ballroom. No LED walls only projectors and some LED TVs.. Bunch of color blasts and shit like that.. Even with all the Lights blacked out the condition still exists... Other microphones/ video sources plugged into the same stage rack are clean.. I am interested about a wired microphone in the same area.. Got a whole day tomorrow to mess around with it.. 
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Kevin Maxwell

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Re: Wireless 60hz?!
« Reply #5 on: May 04, 2016, 11:44:06 pm »

I had a problem at a video shoot where we were getting interference on the truck feed. I was chasing the signal routing using a headphone amp, an older Shure FP12. As I was commiserating with the Stage hands I was saying it would be nice if I had a wand of some kind that I could wave around and see where the interference was coming from. As I was saying that I was animated and waving around the FP12 with the headphones around my neck. And I suddenly realized that the FP12 with the sensitivity cranked all the way would work as a wand. So I put on the headphones and started waving around near things. I discovered that everywhere that the Vari-Lites, over 100 fixtures of them, had noise emanating from the cables everywhere there was a connector to extend the cable farther. So everywhere this was on top of audio cables it caused a problem.

If you have a battery powered headphone amp, crank up the sensitivity and the volume and see if you can use it as a hum detector. With nothing plugged into the input. 
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Scott Holtzman

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Re: Wireless 60hz?!
« Reply #6 on: May 05, 2016, 12:05:31 am »

In the Mayflower hotel in DC, grand Ballroom.. 2 X BTR( A2 and C4)and 12 channels of UHFR.. (H4 and J5) Tested and checked fine... About an hour later the A1, started to complain about a pile of noise on he RF channels and on the Wireless BTR... Chase my tail for about half hour... And located the issue down to a particular part of the ballroom...
So the wireless mics are clean on stage and in other parts of the room, but when I walk down one corridor there appears a 60hz cycle on ALL RF channels.. Now if I stand down the "noisy"corridor and I rotate the handheld or belt pack sideways the noise goes away... Have I created a humbucker somewhere? Happens with all 12 UHFR channels .. And also happens with the TR825 packs... Changed my whole powers scheme around and no change...
So I am living with it.. The RF is crystal clear in all the other parts of the room. Strange... Some iR listen systems operating in the room but I asked him to shut down while I was trouble shooting... Still scratching my head a bit.

The way you are describing this the noise is getting induced before the transmitter in the MIC or beltpack then modulated on the carrier.  I assume the RF signal is strong and the 60 cycle signal is recovered at the AF output of the receiver?

This is very interesting, simply from a troubleshooting process standpoint.

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Benjamin Krumholz

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Re: Wireless 60hz?!
« Reply #7 on: May 05, 2016, 07:46:55 am »

The way you are describing this the noise is getting induced before the transmitter in the MIC or beltpack then modulated on the carrier.  I assume the RF signal is strong and the 60 cycle signal is recovered at the AF output of the receiver?

This is very interesting, simply from a troubleshooting process standpoint.

Yes very interesting.. So how's this for trouble shooting... Pair of headphones directly into receiver.. No output cable connected. You could hear the noise being induced.. But like I said I can take the HHld to another part of the room and it was clean.. Freqs are clean... Turn off transmitter and the line is clean...

Also another note, the inductance seems to be coming from within a pair of columns that my racks are between.. Traced power twice, everything is kosher it seems..
And it happens with my wireless com packs also... Com is wisper quiet but when I key my belt pack there is the hum... Keep keying and turn the belt pack sideways and it is quite..

I always wish my super power was to see radio waves and magnetic fields.
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brian maddox

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Re: Wireless 60hz?!
« Reply #8 on: May 06, 2016, 02:04:04 pm »

...
And it happens with my wireless com packs also... Com is wisper quiet but when I key my belt pack there is the hum... Keep keying and turn the belt pack sideways and it is quite..

I always wish my super power was to see radio waves and magnetic fields.

This description gives a major clue to what is going on here.  You've got electro-magnetic induced hum happening from some sort of fairly powerful AC source, probably a large transformer nearby.  It's inducing 60Hz in the wires and/or transducers that precede the Mic Preamp circuit in your comms or RF mics or whatever.  Since there is considerably gain applied to any signal that appears BEFORE the mic preamp, it doesn't take a huge amount of interference to make for a whole lot of noise.

A wired mic may, or may not exhibit the same symptoms due to the fact that it has a direct connection to ground that may drain off some of the interference depending on a whole lot of other factors.  But anything not attached directly to ground isn't gonna have anywhere to drain that electro-magnetic interference and it's gonna make your life more difficult.

FWIW, i haven't worked in the Mayflower in years, but my fuzzy memory indicates to me that i had all kinds of hum issues in there back in the day.  Between the ancient wiring and the very close proximity of Very High Voltage and Amperage Devices used in the Metro, it's no wonder the place has some interesting challenges.
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brian maddox
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Andrew Outlaw

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Re: Wireless 60hz?!
« Reply #9 on: May 06, 2016, 03:51:03 pm »

FWIW, i haven't worked in the Mayflower in years, but my fuzzy memory indicates to me that i had all kinds of hum issues in there back in the day.  Between the ancient wiring and the very close proximity of Very High Voltage and Amperage Devices used in the Metro, it's no wonder the place has some interesting challenges.

I have worked there as recently as last year, and I can second that. Always some sort of hum or grounding issue. I have had the lights cause noise in my speakers when plugged into wall outlets in the smaller rooms. Never had an issue like that w/ RF though. Maybe different setups and I never had mics go where his mics are going.
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ProSoundWeb Community

Re: Wireless 60hz?!
« Reply #9 on: May 06, 2016, 03:51:03 pm »


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