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.

Historical Retail Wireless Microphone Pricing: 1973-2011

We spent a few hours at the Audio History Library & Museum and gathered a total of 11 publicly available retail price-lists from five manufacturers, and plotted the prices for the most common packaged systems and configurations on the graph below.

These plots should be thought of as visualizations of historical curiosities, from which we can make crude inferences, rather than a deep-reaching analysis.

For a deep analysis we would need price-lists from all manufacturers (we only have a few) across many different years, as well as degrees in statistics.

Although the collection at the Audio History Library & Museum is more comprehensive than anywhere, the best we were able to gather was a stack of snapshots of some manufacturers’ price-lists from certain years. In some cases, we got lucky, and found two price-lists from two manufacturers from the same year.

Furthermore, we did not plot every single model because frequently the difference in price between one model and the next is due to differences in form factor and microphone capsules (custom colors, headworn vs. lav, etc), rather than radio features. We’re much more interested in understanding how pricing relates to the latter than the former.

Here’s the visualization. If you’re on a mobile device, you should be able to turn the device to landscape orientation to read all of the juicy details.

We’re working on getting comments installed on Audio Gloss, hopefully by today, but in the meantime feel free to email me with your thoughts, and I will add them below.

Thoughts on Innovation

The earliest use of UHF band frequencies we found in our limited sample of 11 price-lists was in 1994 by Lectrosonics, in their UM, UH, UT, and UR lines. Some other manufacturer may have used UHF earlier than 1994, but we don’t have a large enough record to say for sure.

In the early days, the 70s and 80s, many models came with a single (that is, one) pre-tuned frequency. A few came with a small number of fixed frequencies. Manual tuning in 25 kHz increments didn’t arrive until later.

The first wireless mic receivers were non-diversity. By the mid nineties manufacturers seemed to offer both diversity and non-diversity models, and by the 2000s, diversity receivers were standard.

Sabine wireless broke the broadcast band mold by offering mics in the 2.4 GHz ISM band, which was originally billed in 2001 as offering “Virtually no RF interference and increased range” and “Up to 50 simultaneous systems.” Now, microphones that operate unlicensed in non broadcast band spectrum are common, like 900 MHz, 1.9 GHz (DECT), and even 5.8 GHz.

Microphones with truly digital modulation have only arrived in the last few years.

Thoughts on Pricing

When you consider inflation, pricing overall has gone down, not up, and the spread between upmarket and downmarket has widened.

That makes sense for a few reasons.

Even though a VEGA Model 55 cost $1,240 in 1973 dollars and $6,646 in 2015 dollars, few users bought more than one.

Before the mid to late nineties, all microphones used VHF frequencies. VHF has larger wavelengths, which translate to larger electronic components and antenna sizes.

Today, a lot of a UHF radio’s circuitry can be collapsed into a relatively affordable and “off-the-shelf” integrated circuit, especially when bought at scale.

Which brings me to scale: economies of them. There are more wireless microphones rolling off manufacturing floors today than there were in 1973. How many more? That’s difficult to say. But we do know that the more units of a product are produced, generally, the cheaper that product gets. And if you offshore some of your manufacturing, as almost all of these companies do to one degree or another, costs go down as well.

It’s also interesting to see, in those cases where we have more than one price-list for the same manufacturer, manufacturers scampering upmarket and downmarket, possibly as an internal strategy, or even in response to other entrants and offerings from other manufacturers.

In 1991, for example, Lectrosonics offered an “Economy Series” with a base model costing only $399. Since then, they have firmly stepped away from “Economy” wireless and staked out a powerful and well-deserved brand as a manufacturer of premier, rugged, and great sounding wireless used in film and TV.

Sennheiser also staked out a valid claim as a manufacturer of top-quality wireless. In fact, their 1999 line is so expensive it forced me to break my scaling! No other commercially produced mic in our survey ever sold above $5K/channel, besides Sennheiser, which has three of them. The SK250-UHF + EM1046RX-UHF combination rings in at an opera-glass shattering $9,725 per channel. I say opera-glass shattering specifically because you are unlikely to find this model outside of a major theater or concert hall.

The high end wireless market is alive and well today, with the Shure Axient series, Sennheiser 9000, and Wisycom lines.

But with economies of scale and increased demand in the middle range, a healthy market for wireless in the sub $1000 per channel range has emerged, providing products that are high quality and affordable for the vast majority of the market, like the Sennheiser EW series, and Shure ULX and SLX series.

There will always be high-end products in broadcast, major rental companies, theater, and film, who will spend five or six figures on a single system, but it’s those 8-12 channel systems that we see so often that are coming in under $10K that contribute to the overall growth of the middle range/downmarket category and, I suspect, the growth of wireless microphone sales overall.

It’s also likely that the 2010 Report and Order that legalized unlicensed wireless microphones under Part 15 rules loosened the collars of many manufacturers and gave them the confidence to really step on the gas to start manufacturing unlicensed UHF microphones in large quantities and targeting price-sensitive markets, as evidenced by Shure’s <$1K/ch heavy portfolio in 2011.

Thoughts on Packaged Systems vs. Configurations

A single channel of wireless audio requires a transmitter, a receiver, and a microphone, which are between two and three physically separate objects.

This presents a challenge to the marketing department, and you see over the course of time different companies deal with this challenge in different ways, and in some cases parlay it to their advantage.

In the 70s and 80s, it was more common for a system consisting of a transmitter, receiver, and microphone capsule to be wrapped up in a package and given a noun for a name, in a singular case. Like, “The Presenter” or, “The Professional.” It’s much easier on the user. They can remember what the thing (which is actually between two and three things) is called, first off. They don’t have to worry about customizing anything, or whether their transmitter will work with their receiver. It’s plug and play. (The last we saw of those types of names was from Shure in 1997, after which time they start to exclusively use adaptions of model numbers and SKUs as product names, even if a string of letters and numbers represents a traditional packaged system.)

But also, one size fits all.

From the very beginning manufacturers offered transmitters and receivers, and sometimes capsules, separately, meant to be mixed and matched in a modular way by the user according to need.

The modular approach requires the end-user to be more technically advanced, and have a good memory for tongue-twisting model names. This seems to be a good upmarket strategy where users are more advanced and know exactly what they need, and might even loosen some screws and fire up the soldering iron to hack and fix stuff themselves. Lectrosonics entire line and Sennheiser’s 3000 and 5000 series fit this mold.

Lower priced systems tend to be more complete. They are plenty of different options, but those options are variations on “kits,” special handheld colors and finishes, one mic capsule over another, or form factor differences, rather than differences in radio components. It’s a great way to create up-sellable options while still retaining the budget-minded base model in price sensitive markets, and without having to invest any significant engineering costs. (It should be said that this practice is not exclusive to downmarket models, as the UHF-R line makes clear)

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

Cross-Industry Coalition Brings Incentive Auction Rulemaking to Screeching Halt Over Concerns About the Duplex Gap

Yesterday the FCC was—at long last—set to rule on the final rules for the incentive auctions. The incentive auctions have been delayed innumerable times, and the Commission, at least the majority of them, were no doubt on the very edge of their seats to hear that gavel drop.

Yet, when a new presentation of clearing scenarios (how stations that are not sold will be repacked into remaining spectrum) was released on the 10th alongside a Sunshine waiver, lawyers throughout Washington representing groups that will rely on unlicensed and other uses of the new duplex gap leapt to their feet. Calls were made, pens burst at the nib, and the rulemaking has now been postponed until August 6th.

Though displeased, Chairman Wheeler could not ignore the letter from the Republican Chairs of the House Committee on Energy and Commerce, Fred Upton and Greg Walden, he found upon his desk this Tuesday, on top of, among other things, a scathing letter from the NAB, and a rare and persuasive cross-industry letter from the following groups:

• National Association of Broadcasters
• Radio & Television Digital News Association
• Microsoft Corporation
• Utilities Telecom Council
• Wireless Internet Service Providers Association
• (WISPA) Engine Advocacy
• Spectrum Bridge
• Consumers Union
• Consumer Federation of America
• Open Technology Institute at New America
• Public Knowledge
• Free Press
• Common Cause
• Benton Foundation
• Rural Broadband Policy Group
• Institute for Local Self-Reliance
• Access Humboldt
• Akaku Maui Community Media

In their letter, they said this:

Placing television stations in the duplex gap will foreclose the use of the duplex gap for both unlicensed users and licensed wireless microphones in important markets. This would significantly undercut the public interest benefits associated with the auction the Commission identified in its May 2014 Framework Order by preventing both mobile news reporting and deployment of low-band unlicensed spectrum in the places where low-band spectrum is most needed to effectively provide these services.

We have a very unusual alliance between diverse and sometimes opposing groups (a political unicorn?) who all want to use the duplex gap for different things, but most pressingly, wireless microphones and white space devices (WSDs).

Over a long period of time they have been assured by the FCC in various ways that they can look forward to using the duplex gap nationwide for these services.

Recently, there was chatter that the FCC was planning on putting TV stations into the duplex gap anyways, in crowded markets, because doing so is an easy way to reduce impairment.

“Impairment” is post-auction interference or coverage area conflict between two or more stations that decide to stay on the air in the same area. It is very, very, verrrrrrrrry complicated to figure out how to repack TV stations into remaining spectrum without stepping on anyone’s toes. A lot of sophisticated work has been done on this tremendous problem.

On Friday the FCC released two clearing scenarios that included many stations being placed into the duplex gap, in order to reduce impairment.

To the above groups, that information seemed to be a punch below the belt that compelled them to move. The groups who want the duplex gap cried foul because the about-face was released far too soon to the Open Meeting to give it serious consideration and debate.

I’ll leave you with an excerpt from a letter the NAB’s Rick Kaplan sent to the Commission Secretary on Friday:

It has yet to be explained exactly why the Commission must hastily roll back its commitment to provide 4 MHz nationwide for licensed wireless microphone operations in the 600 MHz band. At no point in the incentive auction proceeding has the Commission indicated that it was imperative to place TV stations in the duplex gap. If anything, a general consensus had emerged that it would be a mistake to place stations there.

*Leading image courtesy “Sam“.

Vintage Vega Wireless Microphone Ads from the ’70s and ’80s

This Saturday I spent a few hours browsing the meticulously organized files found at the sound industry’s archives: the Audio History Library & Museum.

We are building a basic historical database of wireless microphone prices—which will be the subject of a forthcoming post. Among them were many vintage advertisements for wireless audio equipment of all sorts from every manufacturer. These ads ranged from historically significant, to hilarious, to downright painful.

As many seasoned pros remember, Vega was among the first commercial scale wireless microphone manufacturers, and for many years had market dominance. Since they no longer exist, we think it safe to share some of the early promotional materials dug up from this valuable collection.

I think we can all share a laugh at how far the technology—and marketing sophistication—of wireless audio has come over the years without cheapening the powerful contributions Vega wireless made to the industry.

Enjoy!

The first five are pages from a brochure on all four—count them—four of Vega’s models from around 1975: “The Orator,” “The Professional I,” “The Professional II,” and “The Performer,” which is advertised as “A microphone, transmitter, and antenna, all in one!”

Vega seems to refer to their entire line as “The Cordless Mike, by Vega,” which goes to show how few wireless microphones were on the market at the time, or, just how gigantic a market share Vega owned. That would be like referring to the iPhone or Droid lines as “The Smartphone.”

Up next is the “Professional 55,” which seems to be aimed at broadcasters.

Then we have the “Ranger” and its delightful camp-western magazine spread.

Finally, the “Q Plus Professional Wireless Intercom,” which rewards with a stoic portrait of an end-user.

Just look at those cold, responsible eyes.

It’s as if years and years on the road have desiccated his soul. All human desires and whimsy have been wrung out. What we see is an automaton molded from the old dregs of what was once a man; a sinless, empty being of the night that subsists on dry Folger’s crystals straight from the package and the vapors of an A2’s smoldering Pall Mall. That lives for nothing—

NOTHING—

but the cue.

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.

An In-Depth Look at Wireless Audio for The Public Theater’s Free Shakespeare in the Park

This May, The Public Theater’s Free Shakespeare in the Park opened with a six week run of The Tempest, starring Sam Waterson and Jesse Tyler Ferguson, and continues July 23rd through August 23rd with Cymbeline, featuring Lily Rabe and Hamish Linklater.

Free Shakespeare in the Park, which has been produced since 1962 by The Public Theater, is a storied New York City tradition. It whips people into a frenzy; performances are known to create lines of air mattress toting Shakespeare fans up to a mile long.

Shakespeare in the Park is of interest not only for the caliber of talent and performance, but for the quality of its technical production, too.

The venue, Central Park’s 1,800 seat open-air Delacorte Theater, presents rare challenges to set designers, lighting, and audio engineers.

Outside the Delacorte Theater in the Shakespeare Garden. Photo courtesy Boris Dzhingarov.

When it comes to wireless, the Delacorte is like the worst of both worlds. It frazzles designers with the complications of outdoor productions—wind, rain, excessive path-loss—but also with the insanely crowded urban spectrum found in Manhattan.

Matt Bell, Assistant Audio Supervisor at The Public Theater (who is standing beside one of the speakers for the production in the image that leads this article), said it best when he told me: “We essentially have to load an entire Broadway quality sound system into a natural park.”

This year, The Public made use of two RF Venue products—the Spotlight antenna and Optix fiber-optic remote antenna system—on The Tempest and Cymbeline, and Matt invited us to stop by for a closer look.

Matt holding one of two Spotlight antennas before installation.

All of The Public’s wireless and sound reinforcement are provided by Masque Sound, whose unrivaled expertise in theatrical audio rental, support, and frequency coordination precedes them. Masque works with The Public on the initial build, but also provides support during the production if dropouts arise.

The Tempest and Cymbeline use up to 40 channels of Sennheiser 3532 and Sennheiser 2000 series, along with Shure IEMs, two matrixed intercom main-stations, and three Telex BTR–800s.

The racks are underneath transparent tarpaulin to keep out the rain.

Though wireless is of utmost importance, the unique, intimate nature of Cymbeline’s set design paired with the Delacorte’s unconventional upstage area—an expanse of open water named Turtle Pond—makes minuscule wireless audio signals vanish into the trees.

“There is no bounce to the room or anything to reflect RF back onto our actors and antennas, like you would have in a traditional theater,” continues Bell. “We used two RF Spotlight’s to get our antennas physically closer to our actors. Since they’re low profile, we built them into our set pieces and under the deck, and our antennas are 120 feet closer than we would have otherwise been able to get them.”

The Spotlight’s thin 7mm disc allowed The Public Theater to mount both transmit and receive antennas for some of their UHF equipment directly underneath the actors, maximizing signal-to-noise ratio. They built two of them into the deck, splitting the center mark, with one stage left and one stage right.

The Spotlights are connected to the Optix converters, which, in Matt’s words, “let’s us get as close to the noise floor of the cable as possible.”

“The park is so big,” he continues, “and all of our cable runs are so long that we want to get things down to as little loss as possible, to get the signal stronger. The 2.5 dB loss of the Optix is a whole lot better than our 10–12 dB loss of coaxial cable.”

I asked Matt if he could provide us with RF scans of the spectrum during an actual performance to help visualize the benefits of the Spotlight, which is much easier to show than tell.

Above is a spectrum trace of the entire UHF broadcast band from the perspective of a PWS helical antenna mounted house left. That is, this scan was taken using a spectrum analyzer connected directly to the output of one of the helicals mounted in the audience, pointing at the stage. In previous years, Shakespeare in the Park designers used PWS helical antennas for the entire system, and I believe they still used them for some channels this year, in addition to two Spotlights.

Helicals create a narrow beam of coverage. They tend to dramatically increase the signal strength of signals located in front of the antenna element, while reducing the signal strength of “off-axis” signals on either side. That’s why we see such a heterogenous rendering of signal strengths in this scan. There are many TV stations that appear to be very, very loud. Those stations transmitters are probably on the horizon right where the helical is pointed. Others are less pronounced. These are probably off to the sides of the antenna.

Now, let’s see a scan from the perspective of the Spotlight.

Most of the TV station signals that the helical picked up are significantly less powerful, and some of them have disappeared completely into the noise floor, while the mic and IEM signals (the tall, narrow spikes), the signals that we want, are the same amplitude, or even stronger than they were with the helical.

Since the coverage pattern of the Spotlight creates a “hemisphere” or “bubble” of reception above it and directly around it, while attenuating signals arriving from the far horizon (like the TV stations around Central Park), and because the sound design team has the Spotlight mounted directly underneath the stage below the performers, the signal-to-noise ratio is superb.

Here’s an overlay of the two scans for an even better visualization of just what a difference the Spotlight makes.

The point of juxtaposing these two scans is not to insinuate that there is something inferior about PWS helicals.

Antennas might be thought of as lenses. Lenses can have very different characteristics, long or short, etc, that are appropriate for different situations. You would not use a telephoto lens to take a panoramic photographic, or a wide angle lens to take a photograph of the moon.

The lens analogy is especially apt here because these scans are taken directly from the output of their two respective antennas, so the spectrum analyzer is looking through the antennas and seeing the spectrum from the perspective of the receivers, which is what really matters.

In this case, in Central Park, which has very crowded spectrum, the Spotlight antenna is a better choice for the application. Under different circumstances, a PWS helical or some other type might be a superior choice.

Production credits for Cymbeline include direction by Daniel Sullivan, scenic design by Riccardo Hernandez, costume design by David Zinn, lighting design by David Lander, sound design by Acme Sound Partners, hair and wig design by Charles G. LaPointe, and original music by Tom Kitt.