Video Switchers can mess up your wireless....

[BCAP]

Attached two frequency scan files

_ATEM_OFF.png - ATEM Studio video switcher turned off in the rack right next to (4) Shure SLX4 receivers in the 518-542 MHz UHF band.

_ATEM_ON.png - ATEM Studio video switcher turned on in the rack right next to (4) Shure SLX4 receivers in the 518-542 MHz UHF band.

Same measurement conditions between the two.

The (4) SLX receivers have been in that rack for several years, no issues whatsoever. Recently due to COVID-19 this particular venue decided to upgrade to streaming hardware to help their customer base (note - it's not a theater FYI). I bring this up b/c some of you may have encountered this before and others may not be aware but may run into similar situation in the future.

Needless to say, the 4 Shure SLX4 receivers are having trouble locating the transmitter and dropping out, switching antennas, etc.

Discussion with BlackMagic tech support revealed they have *no idea* that their products are putting out this garbage into the RF spectrum. I have no idea how far up this goes - could potentially cause an issue with nearby ISM, 2.4GHz, maybe 5G low band for sure, or other cell phone frequencies.

Seems to be fairly low power interference, it goes away with distance, but if you install this stuff into a rack next to wireless audio receivers it's trouble IMHO

 

[AudioGreg]

i find not so much the ATEM, but SDI feeds (esp on cheap coax) can emanate all kind of bad RF interference. attached is a look at remote fiber rack I ran into years ago, containing among other things Senn G3 and a SDI over fiber box from Studio Technologies. Cheap coax for the video, routed all over/around the RF cables/receivers resulted in this scan. changing out the video cables to nice Belden SDI cable and moving them away from the RF gear, all of the 12-18 inches the rack allowed, cleaned this up considerably.

 

[FMEng]

Almost any electronics with a microprocessor can radiate some RF. Switching power supplies can also radiate. The quality of the shielding of the cable is certainly a factor.

 

[BCAP]

I think the cable might be the culprit here. I'm going to do some more testing at their venue and perhaps we can address with higher quality cable. I've seen some coax with double shield, maybe that would be an option. I'll provide an update when I figure out the cause.

 

[macsound]

If you're in the mood to do some more scans, I'd be interested.
At one point I installed a cisco switch into a rack with a UPS and sennheiser wireless receivers and got all kinds of RF noise. Turned out to be the power supply for the LED striplight I installed at the same time so I could see what I was doing.

 

[TimMc]

SDI converters and poorly terminated coax were the bane of my existence on a corporate gig I did a couple years ago. Old video vendor with new gear, client wanted HD-quality recordings. I had wireless mic issues that defied new channel scans, on-the-fly reprogramming... 2nd day I went in at 530am and started from scratch. Thought I had everything set to go and the VDO crew came in and started powering up their gear. I'd gone out to the foyer for coffee and when I came back only 4 of my 10 wireless receivers showed no RF. Now I'm scrambling because talent starts showing up to be mic'd in about 30 minutes. I convinced one presenter to stay with wired mic at lectern, put the emcee on a wired 58, and gave the 2 remaining working lav channels to the other morning presenters. We made it to lunch. With rehearsals scheduled for the afternoon, I had some time and got with VDO. Had them turn off all their gear and bring it back online while I watched the RF meters on the receivers. In less than 10 minutes we tracked it down to either an SDI/HDMI converter or the coax patch cables. VDO replaced all of that and the RF noise *mostly* went away. They had some other leaky coax or gear but I bumped the remaining 2 'iffy' channels to full 30mW power and we made it through the rest of the event.

The other thing that will FUBAR your day and you'll have zero recourse - LED video walls. My friend Pete Erskine (RF tech for Clair Broadcast, Tim McGraw, Taylor Swift, more) related a situation where the RF noise floor from an LED wall/floor was so bad that for 1 number, the IEM transmitter antennae had to be dropped in to just a few feet over the performers. Cutting the LED floor or any part of the video was not open for discussion, at all, not a bit, no compromise. Client didn't really like having the visible antennae but it was the only way to get an acceptable S/N ratio at the IEM receivers. Not all LED video panels are as noisy as others and the manufacturer RF emission specs are a little misleading, because nobody is putting up a 250mm x 250mm panel and calling it done. It's thousands of them, and it's the PSU for them along with the video signal distribution infrastructure that makes the difference between "RF noize machine" and "we can do a gig with this".

With the use of LED video panels in theatre on the increase (or it was, anyway) and the limited places one can put receive antennae on stage, this already is an issue when trying to make 40 channels of RF mics, a dozen full duplex wireless intercoms, and the venue's RF environment all work and play nice together. In some cases the video/set and audio designers have had rental vendors put up full or half-size displays to measure RF noise floors and to leave a fudge-factor for theaters in high RF areas.

 

[BCAP]

Thanks TimMc. Wow. That sounds like a nightmare!

I'm familiar with the video wall issues though I haven't had any personal experience with them I know they can cause issues.

I'm going to go back to this venue and try to see if I can further isolate the specific issue if it is resolved by switching cables or converters. I'll update when I get more info - thanks very much for your input & that is very valuable to me.

 

[FMEng]

The SDI cables should be, at minumum, 100% foil plus braid. Foil may not hold up well in portable usage, so double foil plus braid would be better. Belden likely makes both, and their products are excellent.

The inverse square law is helpful with regard to interference. Remember there is -6 dB less signal for every doubling of the distance. A little space between the source of interference and your antenna can do a lot. The same applies with the desired signal from the mics. Use it to your advantage.

The FCC might like to hear about your video wall experience. It sounds like the emission testing needs to be done with a number of panels en masse. It can be prevented with proper design, but the cost of the product will go up. I cry crocodile tears for the video folks.

 

[TimMc]

The SDI cables should be, at minumum, 100% foil plus braid. Foil may not hold up well in portable usage, so double foil plus braid would be better. Belden is the preferred source.

The FCC might like to hear about your video wall experience. It sounds like the emission testing needs to be done with a number of panels en masse. It can be prevented with proper design, but the cost of the product will go up. Tough luck for the video folks.

I think this was the first time their SDI/HD rig was put together outside of their shop. Without having some wireless mic receivers in use at the same time they'd have no reason to suspect a bad cable or device.

Pete has the documentation and the extreme example LED wall/floor cited was from 5 years ago, maybe longer. Those products are no longer touring. Five years, isn't that like "forever" in videoyears?

WWE made extensive use of video floor in their 2018/2019 redesign. That set was assembled in My Fair City, teched at our arena downtown with first show/out with the new stuff. Either the RF folks were on top of things before hand, perhaps products measured prior to purchase, or just that the LED panels and their PSUs are getting quieter... but I don't recall the the RF crew scurrying around like they were fixing things related to noise floor.

 

[BCAP]

Thank you very much for your opinions and suggestions. Very much appreciated. Here is an update.

I was able to get back to the venue to do some more troubleshooting.

After performing a number of different RF scans while unplugging various SDI cables from the Mini Converter / SDI Distribution Box, I found a noisy SDI cable between the ATEM's output and the SDI Distribution Box input. Replacing this cable eliminated of a great deal of broad band RF interference. I don't think the spectrum is 100% free from interference from the switcher or the distribution box, but it is MUCH MUCH closer to what the spectrum looks like with all the video equipment turned off and the wireless microphone receivers are now performing much closer to the way they had been before.

Just to be 100% clear, as far as I'm concerned the RF problem was not with the ATEM or Blackmagic's equipment - as the venue owners and others who work there had initially suspected.

If I were the venue owners I might potentially question the rest of the cables in the installation. They had some long runs to make so their installer ordered bulk cable - RG6 18 AWG, copper cover steel foil with a 60% aluminum braid. It's not Belden or Canare and the ends I could not identify either. I don't want to come off as sounding critical, as the rest of the installation could be 100% fine but I perhaps a cable with even more robust shielding should be used for connections inside and near the rack? I don't know.

Again thank you for your help!!

 

[donboomer]

No doubt that interference caused by out of bound sources can ruin your wireless day. T-mobile’s pink lightening bolts are likely creating IM interference down to about 550MHz and video walls, LED lighting and security radios are coming at you from the low end of the band. Adding simple bandpass filters can make a big improvement to the reliability of your wireless mics.

Bandpass Filters, Part Deux

RF bandpass filters for wireless microphones

www.rfvenue.com

 

[Ben Stiegler]

so a question - were your SLX4 receivers using the factory-supplied whip antennae in the rack, or did you have an antenna distro system with the Rx antenna outside the rack? Lots of questions underneath that one:

- is it an issue of SLX receiver shielding (chassis), vs. antenna input pickup of RFI?
- geometry/positioning/distance of antenna(e) to talent location
- (squelch not adjustable in the SLX4 ... so you're stuck with the hardwired value).

I don't know how it is in your town, but I'm driving clients firmly to replace their analog wireless gear with digital whenever possible. Sometimes there's a bad moment which drives home the point for me. Spectrum contraction etc. is pretty abstract, but "EMT / Fire dispatch traffic overtaking act 2 of the musical" is easy for them to understand, tho painful.

 

[BCAP]

Hi Ben - yes using the standard 1/4 wave whip antenna, with the Shure blank plate installed on the side front so that the 1/4 wave antennas have a ground plane, installed next to the receiver. Antennnas are installed 90 degrees off plane from the transmitters. I will also say in this particular venue the receivers have never had strict line of sight to the transmitters, blocked by wood cabinet - but it has never been an issue so far. Up until the ATEM was installed reception was very very good. The frequency scans (I've done multiple) do seem to confirm the ATEM's involvement in the equation, but I have advised the venue to reposition their receivers for line of sight numerous times over couple years.

Digital wireless (not the 2.4GHz variety I've contributed to other threads about... but maybe Shure Axient, etc.) - Excellent, excellent stuff. I believe it would not be in their budget unfortunately.

 

[Ben Stiegler]

Check out the recently released SLX-D ... low end digital, coinciding with end of life for SLX analog!

 

[rphilip]

Check out the recently released SLX-D ... low end digital, coinciding with end of life for SLX analog!

Info on the SLX-D has leaked but doesn't appear to have been officially announced yet.

Philip

 

[FMEng]

QLX-D is more expensive than analog, but not terrible. Digital can be interfered with too. The big difference is how many units can run in a 6 MHz channel. If you have enough spectrum for the number of units, then you don't need digital.

I went with QLX-D for a recent church purchase, mainly because there's a university with a ton of wireless across the street. The spectrum efficiency made frequency coordination much simpler.

 

[Ben Stiegler]

Info on the SLX-D has leaked but doesn't appear to have been officially announced yet.

Philip

QLX-D is more expensive than analog, but not terrible. Digital can be interfered with too. The big difference is how many units can run in a 6 MHz channel. If you have enough spectrum for the number of units, then you don't need digital.

I went with QLX-D for a recent church purchase, mainly because there's a university with a ton of wireless across the street. The spectrum efficiency made frequency coordination much simpler.

I prefer QLXD for many reasons
its networkable, so I can leave Wireless Workbench running 24/7 and have a record of interference, problems, battery issues ... helpful for when the site calls and goes "Its not working".
- Digital has better noise immunity than analog. Analog wireless audio can degrade as interference levels increase. Digital has check-sums/parity/etc. so that the audio transmission is unaffected right up to the edge of the noise cliff where the interference is overwhelming the error-correction algorithm.
- because networked, I can remotely adjust tx and rx parameters - shifting frequencies, adjusting pads, etc.
- because networked, I can back up the entire rack-o-receivers/transmitters configurations - its all saved in a show file. Very handy for swapping spares, or if you have to quickly configure a batch of rental gear onsite ... you can load a file instead of wasting onsite time plinking away with device buttons.

 

[mbenonis]

The SLX-D system was announced today: https://www.shure.com/en-US/products/wireless-systems/slx_d_digital_wireless

 

[Jay Ashworth]

QLX-D is more expensive than analog, but not terrible. Digital can be interfered with too. The big difference is how many units can run in a 6 MHz channel. If you have enough spectrum for the number of units, then you don't need digital.

I went with QLX-D for a recent church purchase, mainly because there's a university with a ton of wireless across the street. The spectrum efficiency made frequency coordination much simpler.

You raise, in this necro-thread, a very interesting question:

Does WWB6 provide any facility for administrative frequency coordination? Can you tell it "we have these 3 MHz, and the NFL has those 4, and the halftime show has these 6 and the local news people are stuffed in this MHz; only use the part that's assigned to us to put things in"?

 

[Ben Stiegler]

yes, its pretty comprehensive