27.11.17

Metallica backline tech on tackling RF and Wi-Fi interference

Via Metallica TV

Chad Zaemisch, Metallica backline tech and James Hetfield’s guitar tech talks to Tim Kridel about navigating the RF and Wi-Fi interference posed by today’s technologies.

TK: In the MetallicaTV video (above), you talk about wireless challenges such as the size of the stage and interference from the LED screens. You also mentioned the limitation of having to keep the antennas few and low profile for aesthetic reasons. I’m hoping you could elaborate on how you overcame these kinds of challenges on this and previous tours. For example, do you have to tweak the antenna positions at every show? Or do you find the ideal locations after the first few shows and then stick with those the rest of the tour?
  
CZ: The antenna challenges on the latest outdoor tour were primarily with the coverage.  The pattern of the antenna coverage on the RF Venue CP Beam was larger in front of the antenna and minimal behind the antenna plane. The guitars would cut out very easily behind the antennas but that was an acceptable trade off for the coverage. We were covering the 180- to 190-foot-wide stage and the depth increase with the “Snake Pit” in front of the stage.  

The folded pattern of the video screens allowed for a small area upstage of the wing vocal positions that would be a dead zone. We had contemplated flying the pair of CP Beams from the upper video or lighting truss but we didn’t want to add another 100 feet of RF cable or rely on someone else to position the antennas daily. And then there was the wind and weather.  

The placement of our antennas had to be negotiated even with the designer as it was an extremely clean looking stage. Even now in the round in arenas, we are using RF Venue's Diversity Fin antenna for their low profile. We couldn’t get away with setting up six CP Beam tents around the stage in-between the band and the audience. Three small Fins have gone largely unnoticed and are working very well indoors despite the proximity of the Motorola two-way radios everyone uses. They tend to overload the receivers when keyed up within proximity.  
 
The antennas were placed and shared by the three different guitar rigs. All three players would use as much of the stage as possible, so there wasn’t a way to create specific zones.  

It was unfortunate that we had to place the CP Beams so close to the LED screens. When performing an RF scan, we could clearly see the noise floor increase 10 to 20 dB. With the proliferation of large video screens on nearly every tour out there these days, it would be nice if someone thought about shielding or somehow controlling the noise emitted by the 60-foot-tall “RF absorbers” as I called them.  
 
TK: Besides the LED screens, what are some other common and some unexpected source of interference? For example, do arenas and stadiums often have in-house communications and AV systems that create interference, such as digital signage? And how do you work around those?
 
CZ: The local RF landscape could become more crowded closer to showtime with TV trucks pulling up outside but unless I had a major problem, I didn’t have time to investigate.  

In addition to that, there was a tall metal structure that would be put over the drum riser in the event of rain.  This further degraded reception as it was in the path of both antennas. We had no roof over the stage, so you can imagine how many days during the summer we needed rain protection. I wouldn’t even consider setting the transmitters on low TX power.  

Coordinating frequencies with the opening acts is essential as well, at least to avoid any kind of panic. Some days were better than others, given the local TV station channels.  
 
TK: In the MetallicaTV video, you also talked about power challenges such as trying to keep the voltage constant with long runs, generators and different electrical systems in other countries. You mentioned using Furman power supplies to deal with those challenges. Do those boxes pretty much solve all of those problems? Or do you have to do some tinkering and troubleshooting at each venue?

CZ: Power is always a challenge. Over the years we’ve had to explain to local production that they need to ground the stage or that they need to re-run all of the feeder cable under the stage that is making the guitars hum.  

Things were much easier this summer carrying our own power. This cuts down on the number of “construction” generators that like to bog down due to clogged fuel filters, etc. We’ve even run into smart generators that just couldn’t handle the sudden power surges caused by the PA amplifiers and the problems this creates with current draw.  

We now use mostly digital gear which is a blessing these days because of the 100-240VAC input range they tolerate. We often use a Furman power conditioner to level out the fluctuating voltage. I wouldn’t dream of running our racks these days without our uninterruptible power supplies. I rarely worry about the actual voltage these days but rather, the fluctuation or sag when the show is up and running full tilt. 
 
Ultimately, the responsibilities of today’s backline technician have widened to include much more than plugging a guitar into an amp with a coily cord. There’s no way I could navigate the RF and Wi-Fi obstacles these days without the tools of computers and scanners. RF bandwidth is becoming so much more crowded now I don’t feel it’s acceptable to just throw your hands in the air and hope for the best or claim ignorance.