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[Jason Glass]

Thank you once again, Jason. James also recommended using the RF pads on the PSM1000. (https://www.rfvenue.com/blog/2015/08/25/four-proven-strategies-for-fighting-video-wall-rf-interference)

As if it wasn't bad enough with all the frequency ranges being gobbled up by Telcoms, now we have Video Walls to deal with. RF world sure isn't getting any better.

Indeed. And when the video wall is actually a video floor, IEMs are not happy. There's only so much physics magic that an RF wizard can summon...

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[Henry Cohen]

This TX-8 was a prototype.  Production units are much quieter.

[RAD hat on]
The newest hardware version, the TX-8U has significantly improved IM supression and IP3 at all output power settings, though optimal input power remains at the 50-70 mW range.
[RAD hat off] 

[Lyle Williams]

Ok, I'm going to say something that might be impractical in the real world.

It's always hard to mess about in someone else's space.

RF interference should be resolved at the source.  Maybe not this show, or the next, but the video wall supplier needs to be shown spectrum analyser images of the interference they are creating, and told to control their emissions.  That may be better grounding, or ferrites on leads, or buying a better system next time.

[Andrew Broughton]

Ok, I'm going to say something that might be impractical in the real world.

It's always hard to mess about in someone else's space.

RF interference should be resolved at the source.  Maybe not this show, or the next, but the video wall supplier needs to be shown spectrum analyser images of the interference they are creating, and told to control their emissions.  That may be better grounding, or ferrites on leads, or buying a better system next time.

What equipment is required to pinpoint the exact source of the interference in an LED wall? I expect a spectrum analyzer and a highly directional antenna?
Are there highly directional antennas available that would work with the rf explorer?


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[Jason Glass]

What equipment is required to pinpoint the exact source of the interference in an LED wall? I expect a spectrum analyzer and a highly directional antenna?
Are there highly directional antennas available that would work with the rf explorer?


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I mounted one of these on a handle and usually insert attenuation for radiolocation with a spectrum analyzer:

http://www.wa5vjb.com/products1.html

Any passive LPDA Such as the Shure PA805, Sennheiser A2003UHF, or Audio-Technica ATW-A49 would work just as well.

Often, walking around with a PSM1000 pack with its standard whip antenna and listening for telltale whistling works better than a spectrum analyzer for location. Many sources have such wide bandwidth that it's not easy to see their signals on a spectrum trace.

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[Henry Cohen]

What equipment is required to pinpoint the exact source of the interference in an LED wall? I expect a spectrum analyzer and a highly directional antenna? Are there highly directional antennas available that would work with the rf explorer?

Don't need a directional antenna; just a standard omni is fine. The idea is take RF noise floor measurements (in the frequency band of interest) at various distances from the wall relative to the screen powered off. When the wall is turned on, try to take the measurements when the wall has full motion video playing back, or is in full white.

Jason's practice of simply taking the IEM receiver and using it as a gauge as to how close you can get to the wall is also completely valid.

[Henry Cohen]

Ok, I'm going to say something that might be impractical in the real world.

It's always hard to mess about in someone else's space.

RF interference should be resolved at the source.  Maybe not this show, or the next, but the video wall supplier needs to be shown spectrum analyser images of the interference they are creating, and told to control their emissions.  That may be better grounding, or ferrites on leads, or buying a better system next time.

No longer impractical. If the video wall is going to spew RF energy into the spectrum required for production wireless, that must be brought to the attention of the TD or PM. It would be the same as someone keeping bright work lights turned on which affect the lighting design of the show; would anyone expect the the LD to "stop complaining and simply make it work"?

I've had this conversation with numerous TD's and PM's, as well as video wall providers, and whereas it has taken a number of years, most folk now understand the issues and will take steps to provide a quiet wall. Though a good deal of that acquiescence is now easier due to the reputable manufacturers actually producing quite wall systems. (But these of course tend to be the more expensive walls, just like RF quiet LED bulbs.)

[Pete Erskine]

Don't need a directional antenna; just a standard omni is fine. The idea is take RF noise floor measurements (in the frequency band of interest) at various distances from the wall relative to the screen powered off. When the wall is turned on, try to take the measurements when the wall has full motion video playing back, or is in full white.

Jason's practice of simply taking the IEM receiver and using it as a gauge as to how close you can get to the wall is also completely valid.

Last year I was hired to do RF for a musical tour at Clair.  I accepted as long as I could approve any LED walls used in the show and the producer said, that is why they wanted me!

Here are the scans I did for the vertical wall with a TTI and an omni whip.  the vendor set up a 10' by 10' wall with full brightness video program source.

First is with the wall off.
Second is with the antenna against the front of the LED  (VHF most affected)
Third is with the antenna 20' away from the center of the front
and the last is with the antenna close about 1' from the rear of the wall

The led floor vendor had roughly the same scans, also for a 10' x 10' floor.

I approved the vendors and the tour was very successful rf wise.  I was not on tour with them tho for other reasons.

[Andrew Broughton]

Don't need a directional antenna; just a standard omni is fine. The idea is take RF noise floor measurements (in the frequency band of interest) at various distances from the wall relative to the screen powered off. When the wall is turned on, try to take the measurements when the wall has full motion video playing back, or is in full white.

Jason's practice of simply taking the IEM receiver and using it as a gauge as to how close you can get to the wall is also completely valid.

I want to pinpoint if the interference is being generated by the control circuitry, power supplies or the leds themselves, in case some shielding could be added or circuits changed. That’s why I’m interested in pinpointing exactly where the source of interference is coming from.


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[Jason Glass]

I want to pinpoint if the interference is being generated by the control circuitry, power supplies or the leds themselves, in case some shielding could be added or circuits changed. That’s why I’m interested in pinpointing exactly where the source of interference is coming from.


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That's wise. A certain late night TV show that I often work uses PRG LED backlighting and set illumination. The lighting instruments are RF quiet, but occasionally one or more of their controllers cause audible squealing in IEMs. Their emissions are so low and broadband that they're invisible on an SA, but fairly easy to locate with the listening method. FWIW, you need to get extremely close before you perceive the squeal getting louder.  Enclosing the controllers in black wrap solves the problem.

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