The Trouble with Analog FM

Most wireless microphones use analog wideband FM modulation to transmit audio in wireless form.

“FM” stands for “frequency modulation.” In an analog FM system, an RF carrier wave varies its frequency in proportion to changes in an audio wave’s amplitude and frequency. For more on the difference between analog FM and digital see here.

There’s a lot to love about analog FM. It sounds great, has slightly lower latencies (technically, analog has no latency, only delay as the electrical signal passes through components), and is a bit more forgiving of low signal-to-noise ratios than AM and digital alternatives.

However, those advantages come at a cost: FM is a heavy user of spectrum.

With UHF spectrum disappearing just about everywhere, high density wireless microphone users have no choice but to find methods of fitting more channels into less space if they want to continue using as much wireless as they do now.

Assuming no breakthrough technology pops up in the next few years, the simplest and most cost effective strategy for increasing spectrum efficiency in the near-term is to transition most—but not all—wireless microphone users to systems that use digital modulation, while leaving analog FM for applications that need it most.

Today’s top-tier digital technology provides performance specifications more than adequate for the majority of applications (and tomorrow’s will only improve) while allowing a larger number of channels to live together in the same bandwidth.

The trouble with FM.

On its own, an individual analog wideband FM carrier and sidebands at full modulation can consume up to 200 kHz of bandwidth—a lot more than many other forms of FM and AM modulation.

In FM, the radio “intelligence” or speech information is conveyed within the single carrier wave visible as the center spike on the scan below. Modulation also produces useless sidebands flanking the carrier.

Wireless microphone carrier signal and sidebands visible against noisefloor.

In both analog and digital transmitters and receivers, two or more signals interact to create intermodulation distortion (IMD). IMD are spurious signals created as the carrier frequencies of signals are mixed together within non-linear devices. The larger the number of signals in use in a given area, the larger the number of intermods. The quality and quantity of filtering, types of devices in use, and other factors all influence how severe IMD is in practice. It is not possible to completely eliminate IMD, though it is possible to accurately predict where intermods will not be using software programs to ensure desired frequencies do not fall on an intermod product.

Because of its prominent sidebands, analog FM requires more space between carriers for multiple signals to peacefully coexist, and more careful calculations to ensure intermods are avoided. Digital produces sidebands and IMD as well, but they are less prominent, which allows channels to be densly packed together.

Receiver design determines spectral efficiency as much as transmitter design. Modern receivers are pretty good, but they aren’t perfect. They allow waves of slightly higher and lower frequencies into the front-end, sometimes resulting in interference. They also pitch RF frequencies back down to AF by mixing lower frequencies with the received signal to produce intermediate frequencies. This process creates additional by-products that limit channel density.

What we in the industry call “frequency coordination,” with its familar arsenal of techniques and software tools, mostly exists because analog FM technology causes problems. The black art of wireless audio frequency coordination as we know it today is not as necessary when digital radios are used.

Does the industry need a digital transition?

Does the wireless audio industry use analog wideband FM because it is the best of all available technologies for the application? Or does the industry use it because it offers the most reasonable balance between performance and price, or, uncomfortably, because the industry has never had reason to change?

The answer is not black or white, and the “technology” in FM systems is not one individual piece.

It also depends on whom you ask. The average school AV tech might not care one way or another what type of modulation a microphone uses, as long as it works. Ask the world’s leading frequency coordinators working gigs like the Super Bowl or Olympics, and they will often specify analog microphones over digital, for valid reasons.

“I have a lot of reservations about digital radio mics at the moment still,” says Steve Caldwell, one of the industry’s leading RF Consultants, sometimes affiliated with Norwest Productions in Australia. “I will not specify a digital radio mic for use in a large venue. They just don’t cope with the noise floor at all.”

Steve explains that in analog FM the bulk of the transmitter energy is concentrated in a single, narrow carrier wave. With digital modulation, the energy is distributed more evenly across a number of carriers, each of which toggle between different discrete amplitude states.

A digital signal is multiple carriers stacked against one another.
Note the lack of prominent sidebands.

A lot of digital carriers are needed for high quality audio. As Sennheiser rightly pointed out in their petition to the FCC, transmitting high quality digital audio requires a lot of bandwidth, about the same as FM: 200 kHz. Manufacturers may possibly continue to improve the efficiency of digital wireless and get higher and higher quality audio into the same amount of bandwidth (or license technology from other industries that accomplishes the same thing), but progress is slow.

Digital receivers are effectively immune from noise, but are a bit more likely than FM mics to suffer from dropouts caused by weak signal strength.

However where spectral efficiency is important, analog FM’s drawbacks outweigh its benefits for the majority of applications, and the performance of modern digital wireless systems are more than adequate for almost everyone.

For the individual user, analog wideband FM surrounded by modern circuitry is a marginally superior technology to any other at the same price point. Top tier FM microphones provide no latency, very high audio quality, and resistance to interference superior to AM and digital alternatives.

But for all users analog wideband FM is relatively wasteful when compared to other modulation techniques. It consumes a disproportionately large amount of bandwidth and creates interference that crowds spectrum to the detriment of other devices.

“Without a doubt,” says Steve, “we should be keeping the analog gear for applications that need it, or applications for which a digital system will not work… With digital, you can effectively stack digital carriers up side by side, in similar fashion to what they are doing with the digital TV channels, and get a lot more out of the spectrum.”

Make no mistake, Steve and the rest of the world’s best coordinators are doing their part to shift the device population off of analog and onto more efficient technologies, too:

“Currently I am in the middle of resolving the spectrum usage for the European Olympics being held in Baku, Azerbaijan. We are using a good compliment of the Shure ULXD Digital mics, along with Axient, Sennheiser EM3732, and Sennheiser IEMs. Most of that is analog, only the ULXD are digital, but being able to place almost all of the ULXD into a single TV channel is absolutely gold.”

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

Leading image: Vietnam era VHF FM PRC-25 Squad Radio.

When Installing Wireless A/V in Large Facilities, Anticipate Growth

As a Technology Manager, I have struggled with planning ahead to ensure wireless microphone systems will play well together in the future. Some of my installed customers have facilities with multiple floors and rooms that I will continue to add permanent microphones to over the years, or the occasional temporary microphone for special events. Without planning ahead, these additions can easily take previous microphones offline.

Trust me, I learned the hard way, and now you get to learn from my mistakes.

Background

I was responsible for a complex of university buildings with classrooms on four floors: three on the first, three on the second, two on the third, and three on the fourth. At first there were only wireless microphones in the first floor classrooms, and these frequencies were set accordingly to not interfere with one another. However, there were sometimes guest presenters, special events, or professors that would demand to use wireless microphones in other classrooms. We’d bring in microphones—sometimes a single microphone, sometimes as many as 10—at the same time for these events and would inevitably run into frequency problems when the temporary mics and installed mics already in the classroom would collide. This would create a nightmare scenario where static would fill the audio or the audio would drop out altogether. The audience and presenters would tilt their heads back at the sound operator wondering exactly what he or she was doing to cause such a disruptive experience.

As Technology Manager, the fault rested squarely on my shoulders. I didn’t have a “master plan” at the time. I made sure all my installed wireless units in individual rooms had no interoperability issues, but never gave much thought to the fact that sometimes they would all have to be used together. The result was five different buildings with microphones that did not operate as they should when another mic (or 10) was introduced into the fray.

Frequency Coordination

Setting all of your wireless microphones to a master frequency list is important because microphones can interact even if they are on a different floor or nearby building. At the start of a job that has the potential to last for many years, I recommend setting up a hypothetical list of 60 frequencies that are properly coordinated, even if you don’t have as many mics. That way, you can grow into the list as the facility adds more microphones without worrying that the new ones will interfere with the old. [RF Venue note: such a list will need to be periodically examined to ensure frequencies are still clear; new sources of interference can and will pop up over time.]

A pre-coordinated master list also allows devices to work in smaller groups within buildings, and prevents intermodulation when temporary mics are thrown in together for the all-too-common “I need this now” event which takes place regularly on college campuses.

Calculating intermodulation products is not easy. I didn’t get into the industry to do math regularly, so I rely on a number of tools that are available to do the calculations for me. [RF Venue note: free online tools exist that can produce better results than spacing frequencies a set interval apart. IMD tools (some of them free) from reputable manufacturers like WSM, WWB, and IAS provide much more reliable frequency sets. The most reliable, and industry standard, method for producing IMD free sets is to use a software tool in conjunction with a spectrum scan from an analyzer. This is why we built the RackPRO.]

Planning for every classroom contingency.

Use Antennas Correctly

There’s an old saying that goes something to the effect of “garbage in, garbage out.” This saying is especially true when it comes to wireless microphone systems. Slapping a high gain antenna on your system and hoping it’ll cure every issue won’t necessarily solve the problem. If your frequencies aren’t correctly coordinated to avoid intermodulation to begin with, or if you’ve set your frequencies on top of an existing RF source, like a television station, throwing a high-gain antenna in the loop may compound the problem, especially if the antennas aren’t placed well. Certainly high gain antennas have their place, and are quite important and useful when used correctly, but they are not a magic wand that can eliminate all pre-existing problems with the system.

Spectrum Changes

Not only is it important to plan ahead when setting your wireless mic frequencies, it’s also incredibly important to plan ahead when purchasing or specifying wireless microphone operating bands. If you aren’t aware, recently the FCC reallocated the 700 MHz band, rendering many wireless microphones illegal. I had to get rid of 5 microphones when I started my last job for this reason. The FCC plans to reallocate the 600mhz band in coming years. At this point purchasing microphones in the 500 MHz band is safer than in the 600 MHz band.

It’s not that hard to prepare for future wireless microphone installation. In fact, it’s easy.

But one thing is for sure: if you don’t prepare, get ready for some awkward stares from the audience.

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

How to Future-Proof Your Next Wireless Microphone Purchase (In the U.S.)

In the market for a new wireless audio system? If so, you’re probably aware that some types of microphones are better choices than others because of upcoming changes to the spectrum. We put together a list of things you can do, and certain types of mics you can buy, in order to minimize risks.

First, let’s clarify what we mean by “future-proof.”

We do not mean that if you follow these guidelines you will never have to purchase another system again. We cannot promise that this guide will weather unforeseeable changes in technology or government policy in the future that no one can predict.

We mean “future-proof” in the sense that Wikipedia has it: developing methods or strategies to minimize “the effects of shocks and stresses of future events.” (High five, Wikipedia)

Be aware of the timeline.

In early 2016, the FCC plans to hold an “Incentive Auction” to clear some, all, or more than the 600-698 MHz band. (A discussion of what the Incentive Auction is and how it works is outside the scope of this article.) Unlike in the 700 MHz auction which many pros remember from 2008, wireless microphones will not be evicted immediately. They will have up to 39 months to vacate whatever spectrum is auctioned off. Since the auctions are not even scheduled to begin until next year, if one were to purchase a microphone in the 600 MHz band today, he/she will likely be able to legally operate it for the next 3-5 years. There is also the possibility that the auction will fail, or that the repacking of broadcast TV stations will take longer than expected, extending legal operability well beyond 5 years.

For many, 3-5 years is enough time to realize benefits from an investment, and would coincide with typical system lifespan in some high use applications anyhow.

Buy in the UHF “safe zone.”

If you prefer UHF and want to be on the safe side, it’s best to purchase a system that operates below 600 MHz. There is a lower probability that those frequencies will be sold. We don’t know exactly how much spectrum will be sold. There are a number of scenarios. As little as 42 MHz, as much as 144 MHz, or something in between.

But we do know the worst case scenario: everything 554 MHz and above going away. If you want to be on the really, really, safe side, purchase a block/band between 470-548 MHz. This will almost certainly be available after the incentive auctions are complete and well into the future. (Caveat: the spectrum may be available, but not useful. See “unknowns” at bottom of post for more.)

AKG Band 7
Audio Technica I
Lectrosonics Block 470
Lectrosonics Block 19
Lectrosonics Block 20
Sennheiser A1
Sennheiser A2
Sennheiser A3
Shure Band H8
Shure Band G4
Shure Band G5
Shure Band H5
Shure Band G1
Shure Band G50

The FCC would like to auction the T-band (470-512 MHz) around 2020. That is some time away, and the fate of remaining wireless microphones there is unclear. The FCC seems to want to allow TVBDs to operate in T-band spectrum, so that bodes well for microphones and we can expect to have those 42 MHz for the foreseeable future.

Need just one or two channels? Consider ISM bands.

ISM band microphones are a good choice for small venues that only require one or two channels and have low to moderate WiFi activity in their facilities. ISM bands are internationally standardized unlicensed bands that are not going away. There are a few of them, with 2.4 GHz being by far the most popular. Most mid grade digital wireless mics hitting the shelves these days seem to be 2.4 GHz. 900 MHz is also an option, as well as 5.8 GHz, which has inferior propagation characteristics but may become viable as antenna technology improves and other bands grow more crowded.

There are both pros and cons to bconsider when shopping for 2.4 GHz microphones, which we wrote about in this article. 2.4 GHz microphones work well as long as there are few WiFi devices and the channel count is kept low.

Use external antennas and antenna distribution to maximize available spectrum.

Using and correctly placing external antennas is the single most powerful way to increase channel count and ensure reliable operation. Directional antennas increase range and reduce off-axis interference when used correctly. More involved remote and distributed antenna systems using either long coaxial cable runs or fiber optics even allow frequencies to be reused in the same facility. Routing multiple channels through antenna combiners and distributors reduces intermodulation artifacts along with other benefits. Finally, external filters like notch and tuned cavity filters may become increasingly necessary. Right now they are used only by the most advanced users.

Need a lot of channels? Get a Part 74 license, and go digital.

The Incentive Auctions will be most inconvenient for organizations using large systems. They may have tens of thousands of dollars in inventory which they need (not want) to know will still be useable in the near future.

If you routinely operate more than 50 channels of wireless (including comms, in-ears, and IFBs), you are now eligible to apply for a Part 74 license. A Part 74 license gives you two important things: the privilege of using 250mW transmitters, and registration on the White Space Database which entitles you to interference protection from TVBDs (more on TVBDs below). Previously, only film and broadcast professionals could hold Part 74 licenses. In a gesture of good faith, the FCC has broadened eligibility criteria to include most large scale wireless audio users.

If you use more than 50 devices and want to continue doing so after the auctions, it is important to get yourself or your organization licensed as soon as possible. For additional details on pursuing licensure, please contact me at the email address below this article and I will gladly put you in touch with the right resources.

Transitioning to digitally modulated wireless is also another effective way to maximize available spectrum. Digital microphones are less susceptible to intermodulation artifacts than analog frequency modulated (FM) models, so you can fit a larger number of digital mics into the same span. Digital models are more likely to incorporate intelligent radio protocols that sense ambient spectrum and communicate between transmitters to self-coordinate in real time. Some systems may transmit analog FM but use digital technology to self-coordinate, like if you use a Shure Axient system with UHF-R.

A few unknowns…

TVBDs: TVBDs are a new class of device authorized to operate on UHF spectrum. We discuss TVBDs at length here. As of today there aren’t many of them, and those that do exist are limited to rural areas. It is possible that TVBDs will become numerous. Since they transmit on the same frequencies as wireless mics, and are not required to sense other types of low power radios, they pose a significant interference threat to nearby unlicensed wireless microphones. The only way to protect against them is to operate somewhere they are not, or hold a Part 74 license.

We don’t know if TVBDs will ever make it to non-rural markets. But if they do, it’s not going to be good.

Density of repacking: Not all TV stations in the 600 MHz band are going out of business. Some of them will probably choose to remain on the air. They get to keep their broadcast rights and coverage area (give or take), but will be moved down to lower frequencies. The FCC gives additional incentive to stations who choose to move to VHF frequencies, though no station will be required to do so. Since we don’t know how many broadcasters will participate in the auction, or how many of those who do not participate will choose VHF, we don’t know how crowded the remaining UHF spectrum will be post auction.

Frustrating, I know.

A silver lining is the FCC has floated the possibility of allowing wireless microphones inside the legal contours of TV stations. TV contours are what you are checking on when you use a tool like Shure’s frequency finder. Instead, they hint that wireless microphones may legally operate wherever TV signal is beneath a certain amplitude. Technically, it’s best to have a noise floor that is as low as possible, but practically this change (if it happens) will open up many more legal frequencies even if the repacking is dense.

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

Leading image courtesy Daniel Dione.

Another Look at RF for the Super Bowl

The man behind Watson Audio Corporation, Jeff Watson, took on RF PL Tech (AKA Wireless Comms Tech) at this year’s Super Bowl subcontracted through ATK Versacom, as he has for three previous Bowls. He formed the other half of the two departments responsible for wireless during the pre-game, halftime show, and Lombardi Award – the other headed by James Stoffo. Jeff got us some awesome sideline pictures: luscious eyecandy for pro audio nerds and football fans alike.

Jeff worked for eight years at Masque Sound before forming his own company, Watson Audio Corporation, to do freelance RF coordination or, as he puts it, “all RF possibilities.”

“Wireless on the field breaks down into two departments,” explains Jeff. “My department is communications. I deal with people being able to talk to everybody, as well as IFBs.”

Preparation begins days before the Super Bowl begins. “First I lay the hardwire communications for a few days with the ATK Versacom team, then I break off from everyone else for a few days and start getting antennas out, getting coverage, and auditing the frequencies I’ve been given.”

There are about fifty wireless operators on comms and IFBs during the three portions of the event Jeff oversees. For each and every one of those devices, he will rigorously screen the frequencies for reliability and walk test (to check range) each pack no less than six times.

Unlike many events, Jeff and all other wireless operators do not select their own frequencies. They are given a strict list of available frequencies by the NFL’s unique Game Day Coordinator program, which we’ve explored at length before.

So why does the Super Bowl need highly skilled coordinators like Jeff if all the frequencies are already locked into a spreadsheet when they arrive? RF coordination is a black art. What worked on paper for the GDC during site surveys doesn’t always work on game day. With over 3000 frequencies, events like the Super Bowl are anything but cut and dried.

“The first thing that James and I did when we got there was sit down with an analyzer and a list of frequencies and audited everything we were given to make sure that the frequencies were still clean,” says Jeff. “Depending on what pops up, you might submit a wish list of changes up to the GDC.”

Since there are so few frequencies available, the new RAD UV-1G, which uses VHF band frequencies, has really helped open up space.

“A spare frequency at the Super Bowl is kind of like finding the Ark of the Covenant,” he quips. “The Super Bowl is an ever growing monster. We add more and more wireless while they take away more and more spectrum, so to be able to put frequencies into VHF and actually have a few spares has been an amazing change.”

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

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.

Why Coaxial Cable Goes Bad

As far as cable goes, coaxial cable is more susceptible to damage than most. That doesn’t stop many audio pros from whipping it around like any old trampled extension cord. Unlike power cords and CAT5, coaxial cable needs to be handled carefully in order to last, and kept out of certain situations.

One of RF Venue’s employees, Nick, prepares to attach a connector to our RG8X type coax
by snipping away some of the braided shield.

Coaxial cable carries high frequency signals through a center conductor in between a thin tube of braided or solid metals called a shield. Insulation in between the center conductor and shield keeps the two conductors from touching one another. An additional (usually black plastic) jacket is placed around the entire assembly. The shielding stops extraneous RF noise from interfering with the signal inside the cable, but can also be used for other purposes like an electrical ground, remote power, or to send additional signals. Since the shape and condition of both shield and conductor are important, small defects can cause a dramatic reduction in signal quality.

Physical Damage

Damage from rough or improper handling and accidents is the most common type of damage. Coax has a wide minimum bend radius and the distance between inner conductor and shield should be kept as even as possible along the entire length.

Just because a cable looks OK doesn’t mean it is. Damage is sometimes invisible to the naked eye, which is why we produced this video:

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Some of the many possible culprits include:

• One clean hit from a heavy flight case.
• One good stomp from a murderously fashionable high heel.
• Continuous or repetitive stress (creep deformation) from light foot traffic over carpet, etc. Always use drop-over cable covers.
• Crimping due to aformentioned minimum wide bend radius
• Improper coiling. Coax needs to be coiled using the correct technique, which you can watch, here.
• Age. Coax that has been pampered like a baby will still need replacement eventually.

Water Damage

Coaxial cable is not waterproof. Waterlogged cable produces altered electrical characteristics, possibly rendering it useless, or weird. Don’t leave coax out in the rain, even if the connectors are covered since small nicks in the outer sheath can still cause water to enter, and (we really shouldn’t have to tell you this but…) don’t completely submerge cable.

Heat Damage

Polyethylene and polyvinyl chloride are used as insulators. These two plastics have relatively low melting points, and can start to soften at temperatures as low as 150 degrees F. If the insulation is exposed to low heat over long periods of time, the position of the center conductor in relation to the shielding may shift as the hot plastics yield. If the center conductor and shielding touch, signal never makes it past that point. Coax should be kept away from heatsinks, stage lights, and other sources of heat. We have even heard of tightly bent cable shorting after being left out in hot sun.

Connector Damage

The connector on either end can go bad, whether it is BNC, N, or some other type. Sometimes the damage will be obvious, like a missing center pin. Sometimes it will be hard to see, like if the solder has come loose loose behind the connector, or the termination was improperly performed in the first place. Boning up on how to terminate cables is a great way to solve connector problems. Also, severely oxidized (tarnished) silver plated connectors will attenuate signal and should be cleaned or replaced.

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

Leading image courtesy Tkgd2007.