How Adding an External Antenna Can Actually Make Wireless Problems Worse

External antennas are an incredibly effective tool for solving interference and dropout problems of all kinds.

But, it is possible to use an external antenna incorrectly in a way that increases problems instead of making them better, or use them in situations where their benefits are either unwarranted or inappropriate.

Amplification of Interfering Signals

When a stock whip/dipole antenna is replaced with an external antenna, and that antenna stays in the booth or FOH, performance improvements come mostly (but not entirely) from an increase in directional gain.

Directional coverage pattern of the 9 dBd CP Beam.

Directional gain is usually good, because of the effective amplification of signals in front of a directional antenna, but directional gain increases the signal strength of all signals within the antenna’s coverage pattern, not just yours.

Most external antennas are “directional” antennas—in that they have increased sensitivity to radio waves in one direction, and decreased sensitivity (rejection) in others.

A reference dipole antenna has a gain of 2.15 dB. A directional LPDA (aka paddle or shark fin) might have a gain of 4-7 dBd, and helical antennas are available with gains as much as 12 dBd.

High gain antennas increase the effective signal strength by increasing the density of radio energy in certain directions, similar to the way a lens or telescope focuses light into a small space (thereby increasing the apparent brightness to an observer) without increasing the amplitude of the source of the light itself.

Adding a directional antenna at the booth and pointing it at the stage usually makes things better because a directional antenna is “focusing” in on the transmitters on the stage and delivering a stronger signal of those transmitter signals to the receivers.

CP Beam helical antennas backstage, courtesy RMB Audio.

However, antennas aren’t intelligent. Antennas can’t differentiate your signal from someone else’s or a source of interference. If a source of interference (like a DTV station or noisy LED panel) falls in the same direction as the transmitter you want to pick up, the noise will be amplified just as much as the signal.

LED panels and TV stations are the most common culprits in this scenario, but unintentional interference can come from nearly any electronic device, and if another intentionally radiating device, like an intercom or microphone from a roaming news crew wanders into the coverage pattern of your directional antenna which were previously being attenuated, buckle up.

Transmit Antenna Contaminating Receive Antenna

In a rack, IEM transmitters often live right next to wireless microphone receivers. Letting IEMs and mics share a rack while using stock whips/dipoles can result in disastrous wireless because the IEMs are spitting out lots of RF while the mic receivers are trying to listen for very low amplitude RF coming from the stage. Cramped together in a metal cabinet is not the best place for the two species of device to live.

A solution is to separate IEMs and mics into different racks spaced a good distance apart, paired with both antenna combiners and distributors (great refresher at this link if these terms are confusing to you), each with their own separate antenna.

A transmit and receive antenna (CP Beam and Diversity Fin) deployed in Times Square, pointed in opposite directions, and offset horizontally, to avoid contamination.

Sometimes, techs might not separate mics and IEMs into separate racks, but know enough about RF to get rid of stock whips and feed the rack’s combiner outputs into an active signal/antenna combiner and the receiver outputs into an amplified antenna distributor. Unfortunately, if you place the external mic receive antenna and IEM transmit external antennas too close to one another, the comparatively high amplitude RF emitted from the IEM transmit antenna can easily bleed into the mics’ receive antenna, which is looking for very weak signals and may end up picking up or being overwhelmed by the IEMs instead.

We always advise our customers to place transmit and receive antennas at least 10 feet apart, minimum, to avoid unintentional interference between IEMs and mics, and never point the two directly at one another, no matter how far apart they are.

Improperly Deployed or Broken Cabling or Connectors

If you’re using an external antenna, you’re also using coaxial cable to connect that antenna to the receiver or antenna distributor.

There are more links in the signal chain, and therefore more links where mistakes can be made or equipment can malfunction.

When trouble occurs, cables and connectors are usually the last things to get inspected, when they should be the first!

Coaxial cable is fragile and easily damaged. The damage can occur inside the cable, or just as commonly at the BNC or SMA connectors terminating the cable on either side. If you have the resources, always check your cable to make sure they are transmitting RF signal properly.

I don’t have enough fingers on my hands to count the number of times we’ve tracked what a customer thought was a “bad antenna” to a severely damaged cable or missing center pin.

Long cable runs can also cause dropouts by reducing signal strength through in-line attenuation. The longer the cable run, the more in-line attenuation you get. Industry standard RG8X steals about 1 dB per 10 feet. 200 feet of RG8X reduces signal strength by about 20 dB (a lot). Even if you have a directional antenna attached to the front of that 200 foot run with 7 dB of gain, you’re still down 13 dB at the receiver, which can increase the likelihood of dropouts.

Active Antennas on Short Cable Runs

So called “active” antennas do not increase received signal strength at the antenna. Active antennas are just passive antennas with in-line amplifiers on the back.

They are not, should not, be used to “pick up more signal” because that’s not what they do. Rather, active antennas boost the amplitude of the signal gathered by the antenna in front of it to compensate for long, lossy feedlines. Much more on this common misconception here.

Active antennas can be very useful when cable runs longer than about 100 feet are in use, but when active antennas are used with short cable runs the signal delivered to the rack can easily be too strong, overwhelming the sensitive front-end of receivers and causing audible distortion or noise.

We frequently get calls from small venues, churches, and events where FOH or the rack position is near to the stage, and an active paddle is mounted on a small stand on top of the rack and connected to receivers with a 5 foot shorty—the perfect recipe for RF overload and ensuing screeching and hissing over the PA.

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At INBOUND15, Our Two Worlds Collide

A strange thing happened two weeks ago.

Hubspot, the web product we use to manage our marketing analytics and CRM (customer relationship management), held a convention called INBOUND in Boston, as they do every year.

INBOUND was a large, world class corporate conference. 14,000 people attended. There were dozens of intriguing panels and talks. Headline speakers included Aziz Ansari, Amy Schumer, and Todd Rowe of Google, among many, many others. The scenic design of the show and conference hall was superb, as was the A/V design and services.

What’s strange about that?

Well, once we got to the conference we realized we knew a lot of the people working backstage—literally behind the big “INBOUND” letters perched up on stage in Hall B—the people that make the show go off without a hitch.

For us, INBOUND15 was far more than a conference. It was living proof that our customer outreach and marketing using the Hubspot platform is working, and a great chance to see our products in action. All of the wireless microphones used by the keynote speakers were sent through a pair of our CP Beams, a special type of antenna we manufacture called a circularly polarized helical.

Here is one of those CP Beams backstage, to the right of the display.

And up close…

We thought it would be cool to write an overview for two audiences of the INBOUND15 conference from the perspective of the production of the live event.

The first audience, our audience, contains live sound professionals, A/V integrators, and other audio nerds who use RF Venue wireless antennas and distribution accessories everyday, but might like a glimpse behind the scenes at a corporate event of this caliber and scale.

The second, fellow users of the Hubspot marketing platform who attended the events and keynotes in Hall B (the main, big hall), who were dazzled by the lights and colors and flying cameras, and have marginal curiosity in how all that stuff works.

As we have discussed at great (great) length before, the days of stuffy, boring corporate events are a thing of the past. Gone are the shaky spotlights, the screeching microphones. The popup tables with scorched coffee and stale bagels? Nowhere to be found.

Because of flush stakeholders (in this case, the awesome and successful company Hubspot), and the power of live events as marketing and community building machines, the resources and technical expertise poured into today’s corporate events equal or exceed those of even the glitziest music concert or special event.

INBOUND15 was no exception.

Most corporate events outsource the pre-show design work—scenic design, booths, kiosks, animation and other audiovisual content—many months before the event begins. This design work is accomplished by many different design companies and freelancers. Most of the design work in Hall B was done by CG Creative.

Then, the design work is handed off to production companies, subcontractors, and freelancers, who actually bring in cameras, speakers, microphones, projectors, and lots of other cool things to put the designs to work.

At INBOUND15 there were two main areas where production companies worked: the Expo Floor and “Club Inbound,” and the General Session room (Hall B) where all Keynotes and Spotlight Breakouts were done. Freeman Audio Visual was responsible for the A/V support and equipment on the Expo Floor, and they brought in Alford Media, a Texas based veteran event technology support company, for the General Session room.

Alford’s team arrived at the Boston Convention Center many days before the start of the event to begin the grueling process of “load-in,” which is when all of the equipment, carefully packaged in large, black, rugged flight cases, is unloaded from semi-trucks and “loaded in” to the venue.

Time is often short, so there is what appears to be (but is not) complete chaos, as supervisors and stage managers shout at people to put this case here, that case there. Technicians unfurl miles and miles of fiber optic, power, and coaxial cable where it needs to go.

Then, technicians begin assembling and testing the equipment. Cameras get powered up, cranes start flying, audio fader programmed, wireless microphone frequencies are coordinated and, these days, much of it is intelligently networked together via fiber optic or CAT-5 (ethernet) cable.

The stage manager will then typically begin blocking talent or stand-in talent to focus the lights and do tech rehearsals to make sure everything works.

We, RF Venue, work most closely with the second group, the people who actually put on the production, because our products are used to improve the reliability of wireless audio equipment.

Within that second group there are roughly three divisions: audio, video, and lighting. Each of the divisions sets up a “village” out of flights cases somewhere backstage. At INBOUND15, Audio Village, Video Village, and Lighting Village were behind the cyc (short for cyclorama, the big piece of fabric that was stretched across the stage). Here’s Audio Village:

and Video Village:

There is also a mixing console and control station located in the middle of the audience, called Front of House (FOH for short). The picture leading this article was taken from FOH by Allison McMahan, Communications Administrator at Alford Media.

I spent a number of hours backstage with the Alford crew during and in-between keynote speakers, and with our customer and friend, Justin McClellan of Communication Handled, who was responsible for all of the wired and wireless intercoms, monitoring wireless audio frequencies, as well as some video tasks that I don’t fully understand.

Here is Justin at work:

Pretty cool, right?

Here you can see the wired communications rack where Justin controls audio communications between crew members and security. In this case a Riedel ARTIST Digital Matrix Intercom was in use.

The entire audio team consisted of Audio Engineer Steve Ellis, Communications/RF Technician Justin McClellan, Audio Monitor Engineer Ryan Sartel, and Audio-Video Recording Tech Andrew McIntire. The FOH engineer was Steven Pollema, from CG Creative.

Here’s Steve, Justin, and Ryan.

I often compare live event productions to baseball. There are long stretches of extreme boredom punctuated by intense moments of fear and scrambling when something goes wrong or the crew needs to move fast to stop something bad from happening. The stretches of non-activity are especially grueling on corporate shows which go on, literally, for days.

But don’t mistake the nonchalant demeanor of the techs during these stretches for lack of skill or attention. What they do is really, really hard, and they are always paying attention, even if it doesn’t look like it.

Above is an image of the “video flow” chart put together on a dime by the video department. It was dark back there, so I didn’t get the best photograph, but this gives you a taste of the skill it takes to pull off an event like INBOUND.

Modern show technology skills are a mashup of old school hand-me-down knowledge, electrical engineering, IT networking, fine craftsmanship, and the herding of cats.

There are a lot of people who can do it, but very few who can do it well. Alford, Freeman, and CG are among the small number of elite companies that do it well, and that’s why they get booked again and again for corporate events of this caliber.

Now, let’s get into the nitty gritty tech details of the audio equipment used at the show.

Alford was using a new technology at the proof-of-concept stage from Riedel called MEDIORNET, that allows any type of signal—audio, video, lighting controls, communications—to be converted into and passed through fiber-optic cable, simplifying signal distribution and lowering the quantity and types of cables required for a show.

There were five Martin line arrays (big, tall speakers) each consisting of nine MLAs and one MLD. Additional Martin speakers included 80 MLA compacts, 12 DD6s, 32 DSX Sub-bass boxes, and 16 MLA Minis.

That’s a lot of speaker.

The FOH console was a Digico SD5. The monitor console was a Digico SD11.

There were 24 channels of Shure UHF-R (which were using our CP Beam antennas), a few in-ear monitors from Sennheiser for the opening musical act, Riedel ARTIST wired comms, and two racks of Radio Active Designs UV-1G for wireless comms.

This was a big show with a lot of very cool, expensive toys to drool over. We had a blast both at INBOUND15 and hanging out backstage with Alford Media, Communication Handled, and the other contractors and freelancers involved.

Until next year!

Special thanks to Allison McMahan and Alford Media Services for some of the photographs used in this article, including the leading FOH image.

The Tradeoff: Higher Gain Antenna, Narrower Beam-Width

One of the tradeoffs with high gain antennas is that the higher the gain, the narrower the beam of coverage. This is usually a good thing—but not always.

For example, the CP Beam has a gain of 9 dBd, creating a beam-width of 43°. This narrow beam width is exactly what you want if the antenna is positioned a reasonable distance away from the microphones or belt packs on stage (say, at FOH, or in the wings in monitor world). It provides increased range and reception by focusing more of the RF energy into that area. It also attenuates signals that fall outside of the beam, allowing you to strategically place helical and other high gain antennas and point them away from interference sources, like LED walls, and towards the signal of interest.

However, if a high gain antenna is placed in close proximity to talent using or wearing a wireless microphone or beltpack, the talent could move outside of the coverage area of the antenna, causing a dropout.

The CP Beam, actually, is not that directional, if you include the entire field of antenna design, and the polar plot above shows that it will still receive energy 360° around the element, but in differing amounts. In front of the element the CP Beam will increase the apparent signal strength of a signal, to the sides, it will moderately attenuate the signal.

There are antenna designs that have much sharper—nearly complete—rejection of off-axis signals, but we very rarely see these types of antennas in pro audio. The following polar plots show the extreme rejection of various types of “end-fire array” antennas.

End-fire array antenna patterns, the image of which mysteriously appears on WikiMedia with no author to attribute. The left most point of each of these patterns (where you see the small bouquet of smaller lobes, would be located at the center of the polar plots above. Now THAT’s rejection.*

The point is that antenna coverage patterns and (if specified) beam widths should be considered when setting up a system to ensure the antenna allows sufficient coverage for the movement of talent in a given space, especially if there is poor signal-to-noise ratio—which would, were the talent to wander off of the main axis of an antenna like the CP Beam, increase the chances of dropout.

An Omnidirectional Antenna with High Antenna Gain is Impossible to Construct

Lot’s of people want to have their cake, and eat it too. Which is why we’re writing this post, to clear up the misunderstanding; Many want an antenna that will focus RF energy equally in all directions—i.e. a high gain omnidirectional antenna that will provide higher gain and longer range in all directions.

This simply isn’t possible.

That higher gain antennas have narrower beam-widths is a function of physical laws. Engineers have been able to figure out some impressive and acrobatic designs for antennas that shape radio waves in incredible ways, but so far they have been unable to dupe the simple reality that if an antenna focuses RF more strongly in one direction, it will be less strong in another.

There are a number of omni-directional antennas on the market that claim to improve reception while providing an omni-directional coverage pattern. That is, they promise a single antenna will increase signal strength, and therefore increase range equally in all directions. These antennas are usually dipole antennas mounted in a housing that allows remote placement, but are otherwise no different than stock dipoles that ship with receivers.

Sometimes, these antennas are combined with integrated amplifiers and marketed as “high gain omni-directional antennas.” Such language is misleading because as we’ve learned, omni-directional antennas must, if you are using the correct mathematical definition of antenna gain, have low directional gain.

You can have an exceptionally well constructed and electrically efficient antenna with an omnidirectional pattern that may very well increase range, but it is not increasing range through directional gain, but rather in its ability to collect a greater percentage of available RF energy from the environment. For example, a half-wave dipole will probably collect more energy than a quarter wave whip (monopole) antenna that might be used as a lower cost stock antenna on some receivers.

You can also have a high gain antenna that radiates more strongly across one horizontal or vertical plane in degrees of one axis (elevation angles), but not others.

An example of a radiation pattern of a horizontally omnidirectional antenna
but still not truly (spherically) omnidirectional.

These are sometimes called “high gain omni-directional antennas,” and here the use of that term is more appropriate, but not truly omni-directional; the coverage area is like a horizontal pancake, or wheel, rather than an omni-directional sphere. (which, by the way, does not exist. Even the most evenly radiating dipole antenna still has two nulls located at the top and bottom of the element.)

Still, a lot of people want the best of both worlds. They want an antenna that will increase range while allowing their talent to roam wherever they please. That is in part why the Diversity Fin antenna, although not a single antenna, was designed and is now popular. It is effectively able to provide both directional and omni-directional coverage by combining two antenna elements on the same board, and the diversity receiver votes between which antenna has the best signal.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

Leading image courtesy Seth Sawyers.

Polarization, Polarity, and Polar Pattern: What’s the Difference?

We often hear these three terms confused or used interchangeably. Although they all begin with the letters POLAR, they are distinct concepts, and confusing one over the other could lead to grave mistakes and/or people pointing and laughing.

Here are three simple explanations and practical take-aways on the three terms.

Polarization

“Polarization” describes the shape of movement an electromagnetic wave takes on as it moves through space. It is the waves themselves that are polarized, but, since sending a wave through an antenna results in polarization, antenna information sheets will usually include “polarization” as a specification, which describes what type of polarization characteristic the antenna will give to the wave, or which polarization they are most efficient at receiving.

Antennas that are linearly polarized are antennas that restrict the movement of the electric EM field to a single direction as it moves through space, which you might think of as flat, like a ribbon. Within linear polarization, there are two subtypes, vertical polarization and horizontal polarization. These two types depend on however the antenna is oriented in relation to the earth. A paddle antenna that is mounted perpendicular to the earth’s surface is said to be vertically polarized, and if parallel, horizontally polarized.

Waves and antennas can also be circularly or elliptically polarized. In both circular and elliptical polarizations, the electric field spins along a fixed axis over time, sort of like twisting the flat ribbon mentioned above. Here is a video that demonstrates polarization. Helical antennas are the most frequently encountered circularly polarized antennas. The Spotlight antenna is elliptically polarized.

Wave polarization is hard to visualize. This video by Youtube user “Ruff” does a great job of illustrating the concept.

Polarization is extremely important to the deployment of wireless audio systems. The energy that leaves a transmit antenna will be more likely to make it through the receive antenna if the receive antenna matches polarizations with the transmit antenna, and, conversely, if the orientation of linear polarization of an incoming wave is directly opposite to the receiving antenna, you can easily get a dropout! In a perfect and static world, transmit and receive antennas would always be identically oriented. But in the world of wireless audio it just doesn’t happen. Performers are always changing the orientation of transmit and receive antennas by moving around with their beltpacks and handhelds, and waves bouncing off walls and other reflective surfaces usually undergo some transformation of polarization, meaning that waves receive antennas try pick up almost never have a consistent polarization.

Circularly polarized antennas like helicals usually provide a performance increase in both transmit and receive applications, because of the element’s ability to more easily match any possible polarization. Polarization diversity antennas like the Diversity Fin are similarly effective at matching polarization, and when used in a diversity receive system are able to completely eliminate multi-path dropouts.

Polar Pattern

A polar pattern, generally, is a graphical representation of measurements of a transducer’s sensitivity or emission strength along degrees of rotation.

In other words, polar patterns are used to show how a transducer responds to or emits fields according to direction, and measures only one two-dimensional plane of space. The most common transducers that use polar plots in our industry are microphones and antennas.

Here’s a polar pattern from a microphone.

And here are two from the CP Beam antenna.

When we create polar plots for our antennas, for example, we put the antenna to be measured on a special turntable in a special room, and point a reference antenna located a precise distance away at the turntable. We send a wave of constant power through the reference antenna, and then turn the turntable, one degree at a time, measuring how much energy the antenna under test picks up at that point in rotation. Then, we take the data and scale and graph it into a polar plot. Each data point, which contains amplitude and degree, is graphed at the corresponding angle around the center of the graph. Since the antenna is not equally sensitive in all directions, the polar plot shows the amount the antenna varies in sensitivity in different directions.

3D plot of radiation pattern. Courtesy “Cwru3.”

Now, polar plots are very useful but they are limiting in that one polar plot is only one slice of the field. An antenna radiates along an infinite number of planes, not just one. “Radiation patterns” are three-dimensional representations of antenna patterns, but you need very expensive test and measurement facilities to accurately create them, and/or expensive physics modeling software, which is why you don’t often see radiation patterns as a standard specification, though they would be useful. We sometimes will take polar plots for two perpendicular azimuths to give you a good idea of how the antenna responds horizontally and vertically.

Polarity

Polarity is the direction of current flow in a circuit. That is, within one system, however the movement of electrons move through a conductor from one place to another.

It’s no use getting too technical on this one, because it boils down to semantics, and in fact there are some very deep and quantum mysteries surrounding the movement of electrons, that I have no business lending a botched explanation to. The + and – signs familiar to us are distinguishing between one direction from another, rather than concretely “forward” or “back.” In an A/C system those markings have more to do with matching the alternation pattern of current than marking a strictly one-way electron street as in a D/C circuit.

Animation of current flow.

Anyways, when it comes to electrical polarity, consult your user manual. And don’t use the word “polarity” to describe antenna polarization. Electrical polarity has nothing to do with antennas and is not the same thing as antenna and electromagnetic wave polarization.

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Jason Glass Talks Wireless for the 2015 CMA Music Festival

This year’s four day CMA Music Festival shattered attendance records and featured country music’s biggest stars—far too many to list.

The show’s RF Designer and Technician, Jason Glass, owner of Clean Wireless Audio, in conjunction with veteran touring audio provider Sound Image, used a fleet of ten RF Venue collapsible CP Beam helical antennas for all performance RF audio used at both of the Titan’s LP Field Stadium’s two stages, the main stage, and “B” stage.

Jason’s design was unconventional and clever. It solved a lot of the RF challenges that come with large-scale festivals, and he was kind enough to speak with us about how it worked at length.

“This is my third year doing the LP field show,” he says.
“The lighting rig encompasses the stage, it’s a veritable faraday cage. We deploy a number of antennas up in the trussing. This configuration is designed to give the best possible line-of-sight link between the performers on stage and the antennas.”

Jason and Sound Image wanted to give guest artists and their engineers the ability to use their own wireless equipment (which artists are much more comfortable doing), but also recognized that, from a wireless perspective, the positions of monitor world and FOH at the venue were less than ideal for reception. Each act would have struggled with antenna placement.

So instead, he flew seven CP Beam helicals above the main stage, in an ideal, lofted position in the trussing, and three antennas in a great spot in front of the B stage. Artists used all their own equipment, but simply patched into Jason’s antenna system for their transmit and receive links. Jason even deployed a toggle switch of his own design to flip audio from one stage to the other.

“Your ultimate goal is to have a reliable link,” Jason waxes. “You have to have a certain amount of signal-to-noise ratio to open squelches and to provide adequate signal for FM capture. I do path loss calculations in my imagined worst case scenarios. With my artists furthest away from the receiver. I account for losses in free space. I account for gain or loss in each component from the antenna through the cable, adapters, splitters, connectors, to assure that I have a margin of signal strength in my worst case scenario.”

Because Jason so scrupulously calculates all of his variables, to obtain as good an SNR as possible, no RF amplifiers or active stages were used, even though the antennas were remoted with long lengths of coaxial cable. Instead, low loss coax was used to complement the inherent 9 dBd of gain found in the CP Beams.

“Even as well-behaved as our video walls are on this show they still generated a measurable amount of noise. When you have active amplification it exacerbates that noise problem. If I avoid the amplification the noise floor is so low it is almost inconsequential. That’s why I used higher gain directional antennas feeding passive splitters, which in turn fed active multicouplers.”

But why the CP Beams, specifically?

“Well, it seems like over the past year or so more and more of my clients own RF Venue equipment that they employ me to operate,” he explains. “I tested a CP Beam with my VNA tester and I saw that it was very close to the other popular helical antennas that I was using over the years, and when you combine that with how easy it is to pack these things, that they are collapsible, it didn’t take long to put two and two together to see that this was a much more convenient way to achieve the same ends.”

In fact, Jason has been using CP Beams for some time now, and has discovered the performance is superior to helicals he used previously.

“I didn’t risk my reputation with my biggest client at my biggest show solely because I measured the antenna and it looked good. It was because the more I used the CP Beam, in every case I was ending up with very reliable performance. All arrows pointed towards making this a standard, so we did.”

Photographs by David Bean/The Visual Reserve. Illustrations by Clean Wireless Audio.

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Three Passive Splitter Hacks for Antenna Distribution

Here are three simple and low-cost wireless audio antenna distribution configurations using the RF Venue 2x1SPLIT passive splitter/combiner—a versatile accessory we’ve used for years to build affordable wireless racks in conjunction with our antenna combiners and distributors.

Homebrew 8 Channel IEM combiner

This setup effectively creates an eight channel combiner for much, much less than a standalone active 8 channel transmitter combiner.

Route both outputs of two four channel IEM transmitter combiners through a single passive 2X1SPLIT, and finally into a helical antenna.

Were we building this kit out for a customer, it would look like this:

• (2) COMBINE4
• (2) RG8X jumper
• (1) 2x1SPLIT
• (1) 25’ RG8X
• (1) CP Beam helical antenna

Passive intermodulation could potentially be introduced under less than ideal circumstances with this setup, just as it can occur at other physical connections throughout the RF chain.

But, if frequencies are properly coordinated, and the splitter in use has good isolation between ports, harmful harmonics are not likely to occur.

Never use an active combiner in place of the passive 2X1SPLIT, and never directly connect two or more IEM transmitters directly to a passive splitter/combiner like the 2X1SPLIT.

There are some engineers who prefer to use two or more four channel combiners with dedicated antennas, as a measure of redundancy. That’s fine, but remember to space active antennas a good distance apart to avoid near-field interactions that may result from antenna farming.

Diversity Fin DAS

Here’s a request we get all the time: “we want the same wireless microphone to function across two or more rooms.”

We use two Diversity Fins and two 2X1SPLITs to accommodate those requests.

In effect we create a simplified DAS, or distributed antenna system. In a DAS, talent freely wanders through a series of coverage “zones” without fear of losing reception. Signal sent to the same receiver(s) or different receivers depending on the engineer’s design.

Distributed systems can get complicated. That’s why we leave the bulk of the expertise in this area to Professional Wireless, who specialize in DAS.

Spectrum analyzer “wiretap”

If you have a spectrum analyzer, you can “tap” your antenna feed or, even better, one of the outputs on an antenna distributor, using the 2X1SPLIT.

Simply place the splitter in-between one branch of one output of a distributor. Feed one of the splitter’s outputs to the analyzer, and return the other output to the receiver.

The goal is visualize RF from the perspective of the receivers. The nearer the tap is to the final destination of the signal, the better the data the analyzer can retrieve for you, since it is seeing what the system is seeing.

This setup is great for taking a peek at RF activity from the system’s perspective, and for troubleshooting RF where an ambient scan has not revealed anything, but it is generally not recommended for routine operation.

The splitter adds one additional point of failure to the signal chain, and poaches a few dB of amplitude, changing the receiver’s interpretation of the two diversity signals.

If you want to do a wiretap during actual performances it’s much better to tap from an unused output on a distro, or on the cascade output of the final distro in a daisy-chain.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

Common Sources of Interference in Small Venues

Small venues offer an abundance of errant charms. Funky seating, graffitied bathrooms, folk art: they are the authentic backdrops to stages where real music is played.

Unfortunately, they also may offer a minefield of interference to the wireless audio user.

Whether you’re a traveling band that brings their own wireless kit, or an in-house engineer doing their best to maintain an honest, trouble-free venue, you should keep a close eye—and ear—out for these common and frustrating RF phenomena.

Amps and personal mixing equipment

The personal monitor mixers so popular with bands these days are notorious for dirty electrical components that kick out bad RF. Other common road gear like effects pedals and guitar/bass amplifiers can, either through malfunction or poor design, also be a source of radio interference. Since these devices are on the stage, they are in a good spot to interact with wireless transmitters and beltpack monitor receivers worn by performers.

Neon signs

Nothing beats a dive bar for late night jams. Gracing the walls, a garish display of defunct beer logos in kitschy neon tube. Neon tubes use high-voltage electricity to excite the atoms of noble gases sealed inside. Every neon sign has a transformer that steps line voltage up to as much as 15,000 volts. These transformers, especially old ones, are usually the problem. But occasionally electrodes in the sign may arc onto condensed beads of mercury or over to the edge of the tube, causing broadband RFI. Unplugging the sign will put a stop to the interference.

LED stage lights

Although you won’t find too many four-story video walls in small venues, LED lighting is just about everywhere, now. DMX controlled LED fixtures are very popular as multi-purpose effect kits that change colors and swivel around and other such trickery, but they can spew a ton of radio waves. Since theatrical LED lighting may be part of the show, it’s difficult to turn them completely off. Instead, a high gain directional antenna is often used to reject LED interference and focus on the performers.

Neighboring venues

In dense urban areas, or clusters of buildings/rooms common to contemporary churches and corporate campuses, it is not uncommon for wireless audio devices in use by other venues to interfere with their neighbors. The best thing to do, if possible, is reach out to your neighbors and trade frequencies to make sure you aren’t stepping on each other’s heels. Where this isn’t practical, another option is to use a neafield antenna like the RF Spotlight to block out incoming frequencies.

Intermods

We will wait for a future article to fully explain intermodulation. In short, intermodulation artifacts are unavoidable, unwanted radio frequencies that develop through the interaction of two or more transmitters. Proper setup of multi-channel systems must use a frequency coordination program to predict where intermodulation products will be. Professional Wireless’ IAS is a popular option, as is Clear Waves.

Camera crews

Local news station stop by to cover the show? Look out. Camera crews are known for destroying carefully coordinated frequency sets. Not only do they carry their own wireless microphones, but their video links are often wireless as well. Handheld video monitors or camera connections back to the truck can gobble up enormous amounts of spectrum, and an increasingly common technology called cellular bonding, used to transmit live footage back to the studio, consumes every unlicensed band it can find.

Leaky power transformers on poles outside

Electrical grid transformers are responsible for squeezing a tremendous amount of electrical energy down into the 110/20 60Hz A/C that lets you watch TV. Many are heavy coils of wire soaking in a vat of inert oil. Sometimes, they “leak” RF energy as an unintentional byproduct of the voltage transformation. The RF from a sketchy transformer can be so strong it will penetrate venue walls after traveling a few hundred feet. Of course, if you do determine a power transformer is to blame, keep your distance.

WAPs and routers

WiFi WAPs and routers are only of concern when using 2.4 GHz wireless microphones. In some venues like hotels, they can be quite powerful and wreak havoc on your 2.4 system.

Mystery sources

If only we could cover every possible source of interference in one article, but we can’t. Anything that uses electricity has the potential to create harmful radio interference. Anything at all. Sometimes, when you have eliminated all of the usual suspects, the only thing left to do is try and physically track the stuff down. And we explain how to do that in this previous article.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

Leading image courtesy Snoopsmaus

Don’t Let Rehearsals Fool Your Wireless Microphone

Too often, we receive worried calls from techs or FOH engineers that go a little something like this: “We set up and coordinated our wireless during rehearsals on Tuesday, but on Sunday we had the worst dropouts! What’s going on?”

Usually, new variables absent during rehearsal have changed the shape and behavior of the radio environment, causing equipment to fail, even if settings are unchanged.

There is no practical way to replicate the RF environment of a full auditorium during an empty rehearsal.

There is, however, ample evidence for what can be expected to go wrong, so you can take steps to avoid it.

Higher noise floor

When 500 people and their cellphones pack into a building, security and staff power on two-way radios, and stage lights and LED walls turns on, the noise floor of the UHF band typically goes up, even if there aren’t any new wireless audio devices using UHF added to the mix.

Although an increased noise floor may not create dropouts on its own, it raises a mic or IEM’s general susceptibility to other sources of interference.

Technical Director Daniel Scotti and the team at Saddleback Church worked with us to illustrate just how much RF conditions can change between an empty room and a full one.

Here’s a frequency scan using an RF Explorer RackPRO and Clear Waves of Saddleback’s main sanctuary on a Saturday before services, with everything powered down.

And here it is on a Sunday, first during a pre-service run through with mics and IEMs powered on, and then during the actual service.

We scanned the entire UHF broadcast band, 470-698 MHz, so visually these results don’t look as dramatic as they might were we examining only a few MHz, but a significant difference is there. The noise floor rises once devices are powered on, and rises in some places again when the audience is present and service underway.

If frequency coordination was sloppy during rehearsal, its faults can rear up during the actual performance when there is less headroom between the signal of interest and noise.

Frequency coordination during rehearsals should follow best practices and use software programs like Clear Waves or PWS’ IAS to calculate intermodulation products to make frequencies as reliable as possible, rather than “good enough.” Techs should assume RF conditions on the day of the performance will be much worse than they are with an empty building.

Performances in urban areas should also consider the possibility that neighboring groups may also be using wireless audio equipment at the same time. Although wireless microphones are low power, they can still cause interference over short distances or between adjacent buildings.

Is there a concert scheduled for Saturday night at the club across the street? Is there another church also holding services on Sunday at 11:00 AM next door?

If so, consider reaching out to them to exchange frequency lists to ensure you won’t step on one another’s toes.

Line of sight

Wireless audio devices need an unobstructed path between the handheld or beltpack and the antenna back at the rack or remote antenna location. Radio waves are absorbed by human bodies. A human body in-between receive and transmit antennas is not good.

Although we see line-of-sight problems in all markets, it seems to be a big problem for houses of worship. Maybe because audience members do a lot of standing up and sitting down.

“Antennas are often set too low,” says Kent Margraves of WAVE, a top-notch integrator based out of North Carolina specializing in houses of worship, including Saddleback. “FOH guys don’t want to put antennas up on stands, but that’s a terrible mistake.”

External antennas are kept discreetly at eye level, just above the heads of seated audience members. As soon as the first rows in front of the FOH position get up, that clean line-of-sight signal gets snipped.

Saddleback was also kind enough to give us comparison scans for when the audience was seated vs when they were standing.

We’ve circled an area around 550-580 MHz where the physical changes caused by audience position dramatically attenuate received signal strength.

External antennas should be on stands well above the tallest audience member with a clear view of the stage. They can also be mounted anywhere within the facility that also provides line-of-sight—like on walls or ceilings—using long runs of low-loss coaxial cable or an RFoF system like the RF Optix.

“The best systems are not installed FOH at all,” continues Kent. “The receivers are backstage in a production rack and the antennas are flown beside or above stage.”

But we assume you’re using external antennas in the first place. Much worse than a low flying external is burying stock whip/dipole antennas in a closed rack housing, or scattering receivers around the booth.

Radio interference on or around the stage

Any kind of electronic device has the potential to create harmful radio interference. Most devices emit some kind of RFI, but the ones up on the stage are most likely to interfere with wireless audio equipment (especially IEM belt packs) because of their proximity, so the stage should be checked and checked again for culprits.

Bands carry all sorts of troublemakers with them everywhere they go. Amps, keyboards, pedals, effects processors, can all produce powerful interference, whether they are malfunctioning or not. If possible, choose frequencies when all the band’s equipment is powered up.

Kent suggests band members and anyone else allowed onstage be required to leave personal electronics in the greenroom. He also suggests vetting mixing equipment brought by the band for interference before letting it up onstage.

Want better wireless? Download our eBook on three essential concepts for correctly deploying and maintaining interference-free wireless audio systems.

Leading image courtesy Chris Fenton.

Visualizing Directional and Nearfield Antennas in Central Park

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To compare the effects of two different types of antennas (and the effectiveness of the RF Spotlight at reducing sources of interference), we traveled to New York City in search of something most professionals avoid: crowded spectrum.

We brought a camera, a wireless mic, and some other equipment and camped around 59th and 6th, just inside Central Park.

A passive coax switch fed one RF Spotlight and one CP Beam to a spectrum analyzer. The switch and analyzer let us visualize and compare what a wireless microphone receiver would “see” if either of these two antennas were attached at this location.

With the CP Beam, the signals and noise floor within the antenna’s pattern are amplified (under normal circumstances, a good thing if pointed at mic transmitters). With the Spotlight, the noise floor melts away, leaving nothing but signal, loud and sweet.

The unique radiation pattern of the Spotlight creates a “bubble” (as we often say) of coverage that envelopes proximate transmitters while attenuating competing RF outside its boundaries, resulting in vastly improved signal-to-noise ratio.

Contemporary NORTHchurch.tv Improves Wireless with Antenna Distribution

This isn’t the first time we’ve stressed just how important antenna distribution is for high performing multi channel wireless microphone and in-ear monitor systems. But instead of telling, this time we get to show it.

NORTHchurch.tv is a vibrant, large, modern church in Oklahoma City. They are unusual for their size – with 1,400 weekly worshipers they are among the 1% largest churches in the US – but as far as wireless audio is concerned, their story is typical of up-and-coming contemporary churches.

Evolving worship styles and steeper demands from musicians and pastors have steadily increased the number of wireless channels a given church uses from Sunday to Sunday (and other days in between). As channel counts go up, volunteers and technical directors are discovering how difficult it is to control dropouts and interference.

When NORTHchurch.tv decided it was time to upgrade both their sanctuary and A/V equipment for a growing congregation, they tapped a longstanding relationship with Skylark Audio Video.

“These days,” says Skylark’s Aaron Newberry, “more musicians are using mics, in part because of the Hillsong approach. It seems like in the worship world the technical directors are trying to get rid of stage noise. By putting vocalists on one mix, sharing some bodypacks on an EW300 and getting everyone on in-ear systems it gets rid of stage noise and allows them to do be more creative FOH. But, it definitely starts to cause issues when you add a ton of wireless channels.”

NORTHchurch.tv’s Production Director, Stephen Kramer, knows about these issues all too well.

“When I first arrived we had older Sennheiser gear that had an antenna distro with it,” says Stephen. “As we upgraded and added more channels, we just ran transmitters by themselves without distribution. The booth at that point was only 40’ from our stage, but we struggled with random frequency noises, and dropouts when someone grabbed the bottom of the mic.”

In late 2014, with the help of Skylark, NORTHchurch purchased a new console and made radical changes to their audio system, including an antenna distribution package from yours truly, RF Venue. 14 microphone channels were patched through a single Diversity Fin and four DISTRO4 distros. Six IEMs were distributed through two COMBINE4 transmitter combiners and one CP Beam antenna.

A clean rack, thanks to antenna distribution.

Todd Cromwell of Skylark elaborates: “A lot of times in our FOH designs the mics and in-ears are in a cabinet under the booth. That often creates dropout issues. We use distribution to get the antennas out of the cabinet and eliminate any issues that could arise.”

NORTHchurch’s Stephen is pleased. “After we put the new system in, I haven’t experienced any issues with interference while the mic is in use. In fact, I was joking with Steele, an engineer at Skylark, that we’re now picking up way too much signal.”

As NORTHchurch.tv continues to grow, their productions will get cooler and more elaborate, and they’ll likely add more and more wireless devices, be they in-ears, mics, or intercoms for the staff. As is the trend these days, NORTHchurch may want to add additional campuses as well, for which Skylark is prepared.

“Something we are pretty serious about is helping churches that are looking to go into multi-site make the right decisions,” says Aaron Newberry. “Because the costs can get out of control pretty fast.”

With careful planning and help from Skylark, we know Stephen and the rest of the production department at NORTH will be ready for what’s ahead.