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.

AT&T Wants Wireless Microphones Out of 600 MHz Before 39 Months

AT&T filed a comment that stakes out what they believe to be the rights of auction winners in the new 600 MHz band. Chiefly, that they should be able to kick wireless microphones, TVWS, and LPTVs out of their expensive spectrum at their convenience.

We had hoped (although not known for sure) that we might have up to 39 months after the auction to cease operations. Mics would have to move once the broadband networks “commenced operations.”

What, and when, “commencing operations” actually entails is what was debated in the round of comments to this March PN, and what AT&T filed comments for on the 18th.

To be clear: nothing has been decided, yet.

The FCC had proposed that a network would commence, “when it begins site activation and commissioning tests, using permanent base station equipment and permanent antenna or tower locations.”

If this becomes the adopted definition of “commence operations,” we will have a reasonable cushion, because building permanent base stations and other infrastructure takes time.

But AT&T doesn’t want to have to wait to give unlicensed wireless microphones, TVWS, and LPTVs the boot.

“commencing operations” should mean beginning any radio frequency transmissions in the 600 MHz band anywhere in a given PEA… nothing in the Spectrum Act even remotely suggests that a licensee must make a significant capital investment in deployment—let alone provide actual service—before it can freely access its exclusively licensed spectrum in a given market.

They propose giving users 120 days notice after this definition of “commence.”

AT&T makes it very clear that the FCC is not to throw unlicensed users any bones, and they base their arguments on Congressional authority in the Spectrum Act.

While some secondary and unlicensed operators may provide laudable services to the public, in Congress’s judgment such services are not to be protected during the 600 MHz band’s reallocation for exclusive uses. Consistent with this directive, the Commission should not interpret “commence operations” in this proceeding to effectively rewrite the Spectrum Act, granting secondary and unlicensed users a significant spectrum windfall.

It seems the value or services of unlicensed users and LPTVs are getting boxed out by auction bidders and primary incumbents, at least in the comments.

Last week I wrote about NAB’s response to the March PN on commencing operations and unlicensed and LPTV use of the guard bands and duplex gap.

They, too, dislike the idea of unlicensed users hanging out in fleeting post-auction 600 MHz airwaves, especially over the rights of Class A TV licensees.

AT&T was quick to parlay the NAB’s response (the NAB, not typically an ally to cellular) for their own purposes.

…it would “defy logic” to allow unlicensed users to easily clear the guard bands by a date certain while wireless licensees are required to navigate burdensome and time-consuming criteria to clear the spectrum they spent massive amounts to acquire. Even NAB agrees, noting that the Public Notice “continues a disturbing and unprecedented trend of elevating unlicensed operations” above other spectrum uses.

Comments to the March PN are now closed.

Although there are some unprecedented angles to allowing unlicensed devices prolonged or continued access to 600 MHz spectrum, the Incentive Auctions themselves are unprecedented—Chairman Wheeler has said so himself—and wireless microphones are an unusual class of device.

Let us hope that the Commission recognize the importance of a gradual transition out of 600 MHz for the many industries that rely on wireless microphones.

Leading image courtesy Carl Lender.

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

RF Venue Gets a New Tagline—and Website

RF Venue debuted a new tagline yesterday:

“Radiate Success”

Catchy, right?

Our products help audio professionals find success by resonating and radiating radio frequency energy in unique and effective ways.

We also launched a subtle redesign of our website. It loads faster, looks better, and includes a super helpful “FAQ” section on every product page.

CHECK IT OUT.

LPTVs and Wireless Microphones: Friends?

Broadcasters and wireless microphone users are cut from the same cloth.

Some of the earliest inventors of wireless microphones were broadcasters, and they were among the first to widely adopt wireless audio for applications like local newsgathering and coverage of live performances.

To this day broadcasters (as a function of mics operated per organization) are among the heaviest users of the things.

When it comes to the Incentive Auctions, two types of broadcaster, Low Power TV Stations (LPTV) and translator stations, have a lot more in common with wireless microphones than some of the other incumbents: both are at the very bottom of the barrel.

LPTV stations and translators are ineligible for the compensatory checks full power stations look forward to in exchange for relinquishing spectrum rights. Most will have to relocate, and they don’t get any spoils from the relocation fund.

Wireless mic users likely won’t see compensation for obsoleted equipment, and they must share whatever white space spectrum remains with TVBDs.

With so much in common, and so many wireless mics in use at LPTV stations (and full power stations as well), there has been collaboration between mics and broadcasters to communicate just how important the two are to one another. (especially licensed microphones)

But faced with scarce resources, and uncertain legal recourse, the two could just as easily send conflicting messages that starve the Commission of what precious attention it has for these two diminutive players—LPTVs and microphones—both of whom need the same spectrum for different things.

“LPTVs and translators are the dominant spectrum holders of low-band spectrum,” says Mike Gravino, Director of the LPTV Spectrum Right Coalition, who is not shy about how unfairly he thinks LPTVs have been treated. “we are providing the most amount of spectrum, and yet we get nothing from the auction.”

Gravino’s Coalition wants LPTV licensees to benefit from the Incentive Auctions. At the very least, Mike asserts that all LPTV licensees should be guaranteed a channel post-auction because of language in section 6403 of the Middle Class Tax Relief and Job Creation Act of 2012, which contains the enabling Congressional legislation for the auctions.

“Our rights are enshrined there,” he continues. “And if we don’t get some sort of accommodation we intend to blow it [the auctions] up legally, even if we delay it for a while. After the auction and repack happens we have what we call the ‘ROD,’ the right of displacement. Which is the right to come back and find another channel. That means we are going to take up all available whitespace. Any spectrum available will come to us, because we have a priority over white space devices, we have a priority over microphones.”

Though I can’t interpret the validity of Gravino’s legal claims, I do sympathize with the plight of LPTVs.

The LPTV landscape embodies the principle of free access instilled in the UHF broadcast band better than most of the full power stations do.

“Approximately 3% of full power and cable stations are owned by women or minorities,” explains Louis Libin, Executive Director of the Advanced Television Broadcasting Alliance, another industry group representing LPTV and translator licensees. “Approximately 30% of LPTV stations are owned by women or minorities. That’s a huge difference, and I’m not sure how the FCC is getting away with it. It’s the destruction of value, jobs, and diversity.”

Even though LPTV stations are not part of mainstream culture, to those who operate and watch them, like rural, immigrant, and other underserved populations, there is a great deal at stake.

LPTV owners will fight to see their own interests upheld to the best of their ability.

The wireless microphone lobby, small as it is, will fight for the same.

Unfortunately, an important part of what both industries want—exclusive and/or interference free use of beachfront UHF spectrum—will be in terribly short supply, and the spirit of collaboration between broadcasters and wireless audio manufacturers might break down to a scramble if there are hints that spectrum might be given to one over the other.

Last week, the NAB filed a comment in response to a March PN that provided additional details on rules for the post-auction transition, and the definition of a mobile network “commencing operations.”

The NAB and ensuite TVTechnology are incredulous that TVWS (AKA TVBD or WSDs) should be allowed to operate in post-transition spectrum—any sorry scrap of spectrum at all—that is unused by carriers while LPTV and translators are given the boot.

Specifically, the PN said this:

LPTV or TV translator stations in the 600 MHz guard bands must cease operations no later than the end of the Post-Auction Transition Period. TVWS devices may continue to operate in the 600 MHz Band indefinitely, except in those areas in which a 600 MHz Band wireless licensee commences operations after providing the requisite notice to the TVWS database administrator.

In response the NAB:

…the FCC’s decision to displace LPTV and TV Translator stations from guard bands and the duplex gap before a wireless licensee is prepared to commence operations is fundamentally unfair… the Commission continues a disturbing and unprecedented trend of elevating unlicensed operations, in this case unlicensed operations in the duplex gap and guard bands, over licensed LPTV and TV Translator stations.

In this case, it is TVWS. In the next, could it be unlicensed microphones?—who in terms of legal hierarchy are far below LPTV licensees as Part 15 devices, but in terms of absolute numbers dwarf LPTV licensees by a few orders of magnitude.

Whether licensed or unlicensed wireless microphones will get to use the guard bands is, to the best of my knowledge, not yet decided. The March 26th PN was silent on the subject of mics. I expect that if low power TVWS devices are required to vacate guard bands in geographic areas where carriers have commenced operations, wireless microphones, especially unlicensed ones, will be kicked out after the 39 month transition period as well. This will be the case for the rest of auctioned UHF frequencies: no microphones allowed after 39 months, even if the winning bidder hasn’t actually set up their network yet.

But, I’m still holding out hope that wireless microphones may obtain some exemption for the gap and guard bands by reason of their very low power (no more than 250 mW) or the argument about ENG “supercriticality” and the importance of large-scale public events.

How broadcasters react, through written and closed-door channels of communication to the FCC, will be important to the immediate future of wireless audio.

Let us hope, given the importance of wireless microphones to broadcasters—and vice versa—that whatever solutions the FCC offers are beneficial to us both.

Leading image courtesy Ze’ev Barkan.

How to Stop Cell Phones From Interfering With Audio Equipment

Yesterday I stated that blackberry buzz, or GSM buzz, doesn’t happen much anymore. Apparently, it does. Thanks to those who emailed.

GSM buzz is an audible interaction between some cellphones and nearby audio equipment. Dusting off my onomatopoeia skills, GSM sounds something like blip blip blip bzzzzzzz.

Whether it is a form of intentional or unintentional interference probably doesn’t matter to you. It is still interference and must be controlled.

I’m going to approach this in reverse order. First, let’s discuss how to get rid of it. Then, for those still interested, where it comes from.

How to Prevent Cell Phones From Interfering With Audio Equipment

Turn off cell phones

DUH, right? Well, it’s still the first line of defence against GSM buzz, which can’t happen if the cellphone’s transmitter is powered down.

Keep phones away from audio gear

Stages are carpeted in audio gear. The farther mobile phones are away from this equipment AND (very important) their cabling, the less likely they are to interfere. Most good engineers seem to impose an effective but draconian policy on talent: absolutely no cell phones anywhere on stage or off stage. All personal electronics are to be left in the green room, no exceptions, and all those in violation, famous or not, are chastised. Engineers everywhere would be wise to adopt similar policies.

Choke inputs for RFI

If you cannot power down or remove cell phones, cannot control or predict whether phones will be near audio equipment, or just want an additional layer of security, a superb way to reduce or eliminate GSM interference is to add a ferrite core before a cable input. Ferrite cores, or beads, filter RFI (radio frequency interference) collected by a cable unintentionally acting as an antenna, while allowing audio signal to pass through. Here’s what a simple one looks like, courtesy “Omegatron“:

When it comes to GSM buzz, not just any ferrite core will do. You must use one that has the correct number of turns and is made from material optimized for attenuating high frequency GSM signal, which can be anywhere from 800 MHz to 1800 MHz.

The best chokes for pro audio are manufactured by Fair-Rite and snap around a cable. They should be placed at the input.

In the context of wireless audio devices (we’ll talk about general XLR wired equipment next), GSM buzz seems to be more of a problem with mic and intercom belt packs. In some cases it may enter these devices via the cable connecting lavalier or headset to belt pack. The correct size for lav cabling can be purchased from Mouser as part No. 623-0461178181 . The smallest cable outer diameter that this core will fit is 4.3 mm, so, if your lav cable is thinner than that you’ll need to roll some gaff tape or place additional insulation around the cable at the location where the core is placed to ensure a snug fit.

For XLR cables with outer diameters of about 9.5 mm, Mouser No. 623-0461167281 should work, placed anywhere an XLR cable connects to mixers, amplifiers, or rack equipment.

There are other diameter snap-on chokes available but make sure whichever you choose is tuned for high frequencies. The mysteriously named Fair-Rite “Material 61” seems to be the best match for GSM buzz. Other types of ferrite chokes and XLR connectors are not optimized for high frequencies and may not provide much protection against cell phone buzz. You can read more about the theory behind ferrite core suppression and Material 61 here.

What Causes GSM buzz?

This was not an easy question to answer. The internet is in wide disagreement on the subject.

I reached out to the always knowledgable Henry Cohen, RF Design Engineer at CP Communications.

“GSM “buzz” occurs with GSM (TDMA) phones,” he said. “It is when the phone is communicating with the tower on the GSM control channel, which is not power regulated and can be as high 1 watt, depending on the phone model. It is pulsed data bursts and does not happen on the LTE side (the reason CDMA phones remain relatively quiet).”

Phones using GSM standards cause most buzzing. Phones using LTE and CDMA rarely do. GSM networks are less common than they used to be, but are still ubiquitous, and even non-GSM phones may “step down” to other networks for various reasons.

The problem is not that GSM mobile phones are using the same frequencies as wireless audio equipment. GSM networks operate hundreds of megahertz above the top of the UHF broadcast band.

The interference is caused by the rapid rate of on/off signaling between phone and base station at cellular frequencies. If these “pulsed data bursts” are able to leak into the audio signal path, they are rectified by electronic components within the device, often by the first amplifier they encounter, which introduces false voltages at audio frequencies into the signal and, down the line, into audible interference when the signal is converted into audio by a speaker.

If GSM pulsed data bursts do not have an opportunity to enter the signal path, they will not be falsely detected as audio by any of the device’s components. That’s why ferrite cores are effective: they filter out GSM frequencies, and the on/off bursts never make it to the non-linear stages where their patterns are unintentionally converted to audio.

These bursts exist in the form of electromagnetic waves in close-proximity (what we call the “near-field”) to the phone. They enter wherever wires or metals offer them the chance to do so. The most common entry points are lengths of unshielded cable, which act as antennas (gathering radio energy), damaged shielded cable, connectors, PCB boards, or practically anything made from metal that somewhere intersects with the audio signal path.

Correctly shielded and grounded electronics, Henry asserts, are good at protecting audio from GSM buzz.

“The real issue is how audio equipment is designed to handle this radio interference. Properly designed and manufactured audio equipment that complies with AES standard 48 is quite immune to the GSM buzz.”

Cheap or poorly designed electronics are more likely to catch the buzz.

There is also a known gateway in XLR shielding called the shield current induced (SCIN) effect.

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

Ferrite choke image courtesy Karl-Martin Skontorp.

Do Cellphones and WiFi Interfere With Wireless Audio Equipment?

Yes and no—but mostly no.

Cellphones using spectrum owned by wireless carriers for voice or data never intentionally interfere with wireless audio, but can unintentionally interfere through the dreaded “GSM buzz.” (the distinction between intentional and unintentional radiators is here)

WiFi devices—including cellphones that are WiFi capable—can and do interfere with wireless microphones, but only with mics using the 2.4 GHz band, which are less common than industry standard UHF mics.

Cellphone Interference

For all practical purposes, cellular transmissions do not directly interfere with wireless audio devices.

If you are blaming cellphones for wireless problems other than GSM buzz, that blame is probably misplaced.

The majority of wireless microphones use UHF broadcast band frequencies between 470-698 MHz. Almost all cellular networks use frequencies located a safe distance away from UHF microphones. And there are no licensed cellular networks that share frequencies with UHF mics.

It’s possible for interference to bleed out of a given band into an adjacent or nearby band. This is called an “out of band emission.” However there aren’t any active cellular bands anywhere remotely near the UHF range.

It’s also possible for cellphones using WiFi to interfere with 2.4 GHz microphones, which we discuss in the next section.

Where are cellphones? All over the place, depending on model, manufacturer, carrier, and region.

As you can see (actually, you probably can’t—click here for a supersize version of this chart) licensed cellular spectrum does not overlap with current UHF. You can also see 2.4 GHz unlicensed waaaaaay to the right. A zigzag line is used to denote cellular bands, as they are mixed in-between other services.

The 700 MHz band was auctioned to carriers in 2008, and the lower portion of that allocation is close to the upper regions of UHF, but few of the winners have built up active networks there, so we don’t have to worry about out-of-band emissions (yet).

Some of you remember the blip blip blip bzzzzzzz sound that preceded incoming cell phone calls in the early to mid 2000s, which was known variously as the “blackberry buzz” or “GSM buzz,” and laid waste to unsuspecting PA systems.

The buzz was a radio communication protocol used by some (especially 2G) GSM type networks that would, under certain circumstances, be converted from electromagnetic energy into audio frequency signal by unshielded wires within electronics acting as antennas in combination with diodes and transistors, and then made audible by speakers.

Some believed that the dreaded buzz was caused by cell phones “taking” mic frequencies. In reality this type of interference is unintentional and caused by electrical interactions between cellphones in close proximity to XLR cables, speakers, and PA systems.

With new protocols like 4G/LTE, GSM buzz is now rare. I haven’t heard it in years (have you? email me, because I would like to know if it still happens)

[UPDATE: After a few emails, GSM buzz may be a more significant problem than is led on in this article. Stay tuned. DOUBLE UPDATE: An important follow up article is here.]

WiFi Interference

WiFi devices, like wireless routers/WAPs, can easily interfere with wireless audio equipment, but only equipment that operates in the 2.4 GHz band. UHF broadcast band equipment using 470-698 MHz is not adversely affected by WiFi.

Most (but not all) WiFi equipment uses unlicensed frequencies on the 2.4 GHz ISM band, which in the United States stretches from 2.400 GHz to 2.483 GHz. The most familiar standalone WiFi device is the wireless router or WAP. But Bluetooth, Zigbee, and many other radio technologies use 2.4 GHz.

2.4 GHz band wireless audio gear includes Line6 microphones, the Sennheiser EW-D1, the AKG DMS-Tetrad, the Shure GLX-D, Tempest 2.4 GHz intercoms, and a few others.

2.4 GHz microphones have grown in popularity because they require very little frequency coordination and are legal and unlicensed in every international region.

However, 2.4 GHz is a crowded band, and most technology operating there does not require real-time uninterrupted operation, like wireless mics do.

One or two channel 2.4 GHz microphone systems usually perform well. But interference may become problematic on multi-channel systems or where WiFi utilization is intense.

Since WiFi is such a prominent feature on smartphones, the 2.4 GHz band is hostile territory anywhere there are lots of people and WAPs that offer up connectivity. Smartphones aren’t just using WiFi for internet access. Increasingly, phones make calls through dedicated “voice over WiFi” apps or through what’s known as WiFi offloading.

Controlling interference from WiFi is difficult for two reasons.

First, WiFi sends out rapid bursts of RF that constantly and unpredictably hop frequencies—unlike analog transmitters which stay on a single frequency. You can’t manually coordinate around a WiFi device because it doesn’t stay put.

Second, WiFi is everywhere and used by everyone, but controlled by few. You have no authority to ask IT departments and cellphone owners to stop transmitting, and no opportunity to coordinate with them. Even if you did, short of completely powering them down, smartphones and other consumer WiFi radios operate automatically and out of direct control.

It is worth noting that both WiFi and cellphones can cause spurious interference to wireless microphones of any type by way of malfunctioning power supplies and poorly designed or shielded electronic components. But this risk comes from anything that uses electricity. Low power cell phones and routers manufactured to tight specifications are much less likely to cause spurious interference than things like faulty electrical wiring, breakers, audio amplifiers, and power lines, so if you are constantly worried about cellular and WiFi as a source of interference aside from the characteristic GSM buzz—you shouldn’t be.

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