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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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.

Protect Antennas and Wireless Gear from Rain, Basketballs, and Other Hazards with Transparent Domes

We often receive calls from installed A/V professionals looking for a way to mount one of our external antennas safely in a school gymnasium, or outdoors somewhere in an ideal location but safe from the rain.

You shouldn’t completely enclose an antenna in anything if you want it to work well. And using protective covers made from wire or mesh is almost guaranteed to cause wireless problems.

That’s why we were thrilled to learn of a solution that Dave Kint, Vice President of dk communications, inc., discovered in the course of working with some of his clients out in Colorado: an affordable transparent dome made of special acrylic.

Dk communications is up to some cool stuff, and Dave has high standards. He knew he needed to mount his Diversity Fin and WiFi router in an ideal, lofted position for excellent line-of-sight, and protect them from wind, rain, basketballs, footballs, and baseballs in the multiple school gymnasium and football field venues he has as clients, without sacrificing wireless performance. Plus, why not try and actually make it look good, too?

After a bit of research, Dave found California Quality Plastics, which manufactures a durable, RF permeable clear acrylic hemisphere/dome that fits over an external wireless antenna and easily mounts to any architectural surface. Dave uses the 24” diameter model, part HEMI24. Navigate directly to this model by clicking here.

“Before we found these domes,” Dave explains, “we really didn’t have anything that would allow us to put antennas in an area where it was going to be susceptible to some sort of damage or impact. I’ve talked to other people about non-metallic metal boxes, but, that didn’t really pan out. They are very expensive, and the other problem is that there’s nothing that’s really of adequate size for the antenna to fit inside.”

Dave notes that California Quality Plastics hemispheres are UV resistant, so they won’t become brittle or discolored after years of sitting out in the hot sun. There’s also enough space for dk to include other wireless gear: “We also were able to put the Apple Extreme under the same antenna dome so that we could use that for Airplay connection and system WiFi control of the DSP controller.”

Typically, we don’t recommend placing wireless devices so close to one another, because of the risk of out-of-band interference bleed over, as well as the metal in the Apple device altering the electrical characteristics of the Diversity Fin.

But, he says it works great and the DFIN is as effective as ever.

Thanks for the tip Dave!

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

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.

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

RF Venue Co-Founder Robert Crowley Talks Product Design

Meet Bob Crowley, RF Venue co-founder, and a man of varied scientific and entrepreneurial laurels.

Some of you may remember Bob from the days of Crowley & Tripp microphones. Besides actually building the things, he was the voice of Crowley & Tripp on the popular blog Microphonium, where he exploded all sorts of microphone myths and scooped up a cult following.

Well, Bob is still very active in wireless and pro audio. Although we don’t hear much from him on Audio Gloss, he leads many of RF Venue’s R&D efforts behind-the-scenes.

I sat down with Bob to let him explain our unique approach to electromagnetic innovation and, in particular, the concept of the physical layer.

AM: What is the physical layer?

RC: The physical layer today is generally used in reference to networks, and most commonly in reference to whatever way bits get sent around, physically. Through the ethernet wires, through the actual physical transformation of electrical signal into radio wave signal or from one place to another.

There is an analogous physical layer that’s becoming more and more distinct in wireless microphones. The reason is because the wireless microphone transmitters and receivers are becoming more sophisticated. They are becoming digitized, being networked.

The physical layer for us means the actual analog modulator, transmitter, radiating antenna, how that antenna radiates through space, the receiver antenna, coax cable, distributors, so on and so forth. In other words not software, not even firmware, but the actual physical stuff that does the heavy lifting.

It makes sense to solve some problems with software. You can introduce things like frequency selection or agility, spread spectrum (which still use the physical layer by the way), but there is a lot of emphasis on these types of software solutions to problems in the physical layer.

AM: Why do you think manufacturers overall have skewed their solutions to higher layers in the network architecture instead of doing what seems to me, perhaps because I have spent so much time with you, to be more obvious and straightforward, which is address it on a more fundamental plane?

RC: The answer is, because the Radio Art, capital letters, is old. All the physical laws and realities are known, maybe not all appreciated, but they are known. Whereas the other areas, software and firmware, computing, so forth, that’s new, and so this is where the attention is drawn towards.

There’s a very well known process that we have carried through all of our businesses, which is we go back to the basics. We go all the way back to the beginning of time in the field, for instance, all the way back to Marconi, or all the way back to Heinrich Hertz and say, ‘if Hertz was here, what would he do about this problem?’ Hertz, for instance, very clearly demonstrated cross-polarization fades. He showed it the very first time radio waves were ever demonstrated. So, you would assume that anything and everything that could be done about it has been done about it.

Well, that’s clearly not so.

When we introduced the Diversity Fin antenna that took advantage of this very well known knowledge about cross-polarization fades, that was something that had not been thought of. And there are lots of things that have not been thought of. Can you think of any?

AM: I’ll need a minute.

RC: That’s the hard part. You have to go back to the basics, reanalyze the problem, and say ‘what have people missed?’

AM: Explain how some of your other businesses have used this methodology.

RC: We learned from Crowley and Tripp microphones that having more signal and lower noise was always beneficial. There was never a case where it wasn’t worth it. Isn’t that obvious? Shouldn’t everyone think to do that? The answer is no. When you look at all the equipment that’s out there and the designer has said, oh well, all I need is somewhere between 10–20 dB and I’ll be fine, and they’ve designed the system around that. Well, that’s great for the average condition, but we’re interested in the exceptional conditions; Extreme congestion, the areas where there are likely to be dropouts, which will be infrequent but severe, those types of things, in order to improve that 99% reliability, which isn’t good enough, into a 99.999% reliability, which is what people need.

RF Venue is all about that.

Our antennas; Why are they so popular? Because they work very well. They gather a lot of signal, or the right signal, or some combination of those two things.

Of course it doesn’t help if you can’t see signal, or can’t measure it somehow. That’s why we’ve introduced products that examine the spectrum. The industry in general is interested in that, but not everyone knows how to use an Agilent spectrum analyzer. Those are complicated. You see a bunch of lines on them and you don’t know what they mean. So, the information has to be put into context to make something people can use.

AM: We’ve been talking about signal, I think maybe we can talk about spectrum. At this point, most people seem to know that the spectrum we currently use is going away, and that the government and cellular industries are exerting pressure to make that happen.

RC: The government has long granted exclusive use rights for certain portions of the spectrum for the public good. What changed was the advent of cellular technology in the 1970s, and the need at the time to get private industry to invest in wide area networks that could use these things. And so the FCC and Congress agreed at that time that the way to incentivize it was to grant licenses, for a long time, potentially forever, to companies that build out the infrastructure.

Pretty soon the 832 channels that the FCC allocated got filled in metropolitan areas, and so there was the need for more spectrum. Sensing money, and the potential for adding cash to the government coffers, the US congress directed the FCC to make more spectrum available for wireless operators and sell it at auction at a price, which at that time they felt was very high, millions of dollars.

AM: Tens of millions of dollars!

RC: Which today seems like a joke.

AM: And this was later than the 70s.

RC: This was in the 80s, less than ten years later. Now, we’ve got this intense demand for broadband devices. Of course, you can’t drive your car unless you’re texting. It’s impossible to drive unless you’re looking down at your phone. If you think of the number of people who are willing to pay anywhere between $50–100 a month to do this, and multiply that times 300 million people, the economic pressure is intense.

There’s this assumption that if people want to use the spectrum and it’s good for business, we’ll just keep giving them more spectrum. Except, a few people realize that this is now starting to contradict Congress’ and the FCC’s original intention to allocate the airwaves in the public interest.

The UHF band became one of the first areas where real, good, regulated mixed use of the spectrum was occurring, which had wide economic value. There were a lot of things that were allowed in the UHF bands, besides TV stations. Studio transmitter links were one of the first, and then there were all kinds of other wireless devices, and wireless handheld communication devices that were permitted in various locales, including microphones.

UHF TV band happens to be a pretty good place to be if you are using cellular telephones, because the antenna efficiency for a cellular handheld at that frequency, which is about fifty or sixty centimeters, is pretty moderate. It would actually be better if they were up towards 1 GHz. But, the AT&Ts of the world want to take the easy route, and they want to go down in frequency, and so that’s why they are highly covetous and willing to pay billions of dollars for 600 MHz spectrum. They caused all the TV stations to move down, and now they’re talking about making the TV stations move again, back down to VHF. It’s crazy.

AM: Well, the counterargument I hear all the time is that people want data, they want cellphones, more than they want the now, from our perspective, deprecated services, like over-the-air television.

RC: Naturally the part that raises the biggest question in terms of public policy in the United States, Canada, and now Europe is the recognition that there are a lot of people who aren’t served by the internet. That was one of the Obama initiatives. There’s a directive that Wheeler talks about from time to time to get cellular operators to provide broadband services out to these underserved, thin areas where it’s not profitable.

AM: I think that’s called the Connect America Fund. So if TV stations are less important than ever, wireless microphones must be even less important than that, right?

RC: Wrong. Innovation arises when spectrum is allocated for the public good. Look at WiFi and the crappy little bit of spectrum they’ve been given. It’s criminal if you ask me, and could be greatly expanded.

If we’re going to be given little slices of spectrum, then we have to make good use of it. There’s going to be traffic, sort of like driving a motorcycle on a highway. You want to be able to see all around you, and be able to control the direction of your signal, so that you can get from point A to point B successfully so you can do your show, or have your broadcast, or have your service without a lot of pff and bzzz, and that’s what RF Venue is doing.

AM: Give me one concrete example of how we’re doing that, now.

RC: The great example of that is the RF Spotlight which in highly congested area knocks down, for example, the huge amount of signals you find at a convention, and focuses only on the local signals that you want to pick up. You aren’t interested in what’s in the hall on the other side of the facility. You’re interested in the speaker who may have a wireless body pack and headset microphone. Instead of following the dictum of putting antennas up high which is antiquated, it puts the antenna on the floor so it only picks up high angle signals and ignores unwanted signals on the horizon.

Look, the founders of RF Venue are spectrum users, who have made excellent use of the available spectrum to develop medical devices, new technologies, patented technologies, inventions of all kinds, and you need access to spectrum to do these types of things. If we lose our access to spectrum, then it is only the AT&Ts of the world that determine how spectrum is to be used.

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.

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.

Paddle Antennas are 50 Years Old; It’s Time for Something Better.

Years ago, while RF Venue was in early stages of R&D, we spent a lot of time in the field observing wireless mic systems and how they and their operators worked in practice. We were not surprised to find many of the common antenna techniques are derived from broadcast radio and television technologies. The first wireless microphone pioneers and power users were broadcast engineers working on TV and film productions, after all.

Broadcast engineers are schooled with book knowledge written for extremely high power transmission scenarios developed for military use and amateur radio – some of the fields where kilowatt transmitters are commonplace.

For better or worse, the methods and rules-of-thumb for high power applications were transferred to the domain of lower power wireless microphones. Things like maximum gain for long range operation, a fixation on gain structure, active paddle antennas, ¼ watt transmitters: these methods and tools worked (and still work) adequately well for wireless microphones under most conditions.

But from our field notes – which were taken at run-of-the-mill hotel ballroom events, schools, and small music venues (where more than 90% of wireless mics live) – we observed time and time again that gain, power, and range variables were rarely the problems.

Rather, we hypothesized cross-linear polarization fading and multipath interference were the root causes of maddening signal dropouts.

After confirming our hypothesis under controlled conditions in the laboratory, we developed and ultimately patented a new polarization diversity antenna system, the Diversity Fin, to specifically overcome the shortcomings of the spaced paddle approach for wireless microphone systems.

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The Diversity Fin is the first novel antenna designed specifically for wireless microphones since the early broadcast pioneers adopted the LPDA (which was patented around 1959).

Polarization diversity, the engineering concept underpinning the Diversity Fin’s innovation, is widely used for cellular applications where moving radios (cellphones), space (real estate for antenna towers), and real time transmit/receive audio are major factors. Sound familiar?

When two paddle antennas are arranged parallel to one another (as LPDAs commonly are) they are much more likely to receive signals polarized along the same orientation. If waves (coming from the mic transmitter) arrive off-axis to the orientation of the LPDAs, fades and dropouts are possible. If waves arrive perpendicular to the antennas, dropouts are even more likely. These might happen when the performer tilts the microphone or even more commonly as a microphone moves around a stage and the orientation of the signal changes due to reflections in the room.

The cross-polarized Diversity Fin eliminate both cross-polarization fades and multi-path interference by reducing the probability of their occurrence. In other words, when using the Diversity Fin the probability of encountering these two types of interference is orders of magnitude lower than when using two paddles.

The Diversity Fin contains two antenna types oriented perpendicularly (orthogonally) to one another. A vertically polarized LPDA, and a horizontally polarized dipole. The two elements are not simply glued or stapled onto each other; they are coincident to the same electrical center point. A coincident cross-polarized antenna will receive waves of any polarization. Since multi-path reflections change the polarization of the wavefront, as well as the length of the path, the Diversity Fin is able to conquer multi-path nulls by sending signals arising from waves of different polarizations to the diversity receiver. It does not matter if the waves are 180 degrees out of phase. (For an in-depth technical explanation, take a look at this whitepaper)

Because the Diversity Fin uses two antenna elements, each with slightly different gain, receivers behave differently while a Diversity Fin is attached. With traditional paddles, the discrimination circuit inside the receiver usually hops rapidly back and forth between one antenna (“A”) and the other (“B”) as the signal strength varies by minute amounts. With the Diversity Fin, the receiver tends to stay on whatever channel the LPDA element is plugged into, and switches over to the dipole element when a multipath null occurs, when the transmitter orientation changes, or when the performer wanders out of the coverage area of the paddle.

The two polar plots of the Diversity Fin LPDA and dipole
element coverage patterns juxtaposed.

This is a good thing, because every time the discriminator circuit is triggered, a tiny bit of noise slips into the audio. If you listen carefully to audio coming from a receiver using twin paddles, and then compare it with the same receiver using a Diversity Fin, the audio will be substantially cleaner.

Additionally, the Diversity Fin has two outputs onboard – one for each diversity channel – and yet takes up half the space of two paddle antennas and only requires one wallmount position or mic stand. It’s easier on the wallet and easier to fit into small spaces – including a mountaineer’s harness, as this video from adventurer and cinematographer Pablo Durana attests:

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Wireless microphone users are numerous, and their operating requirements are unusual; they should not have to rely on merely acceptable technology borrowed from other industries. They should have an antenna engineered to perform exceptionally well under real-world conditions. The Diversity Fin is that antenna.

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.

The Top Three Wireless Microphone Problems and How to Solve Them

Wireless microphones are prone to interference, noise, drop-outs, and many other, and more severe, RF problems. These problems can be disastrous for both live productions and installed systems. Everyone remembers an embarrassing time when a wireless mic suffered harsh static or intermittent dropouts. Malfunctions lasting even a fraction of a second can destroy presentations and performances, while making everyone involved as crazed as a pack of feral hogs. Below are the three most common problems, and a few basic techniques to solve them.