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Wednesday, March 23, 2011

Wireless Technology Series: Audio-Technica SpectraPulse

This is the latest installment in a series detailing the latest technology in wireless microphone systems.

The SpectraPulse wireless microphone system from Audio-Technica is one of the more interesting products to enter the market.

It was announced about two years ago and appears aimed mostly at installed sound applications, specifically boardrooms and courtrooms where operating range is not so much the issue, but data security and ease of use are important.

The system represents a fresh approach in its form factor, technology and performance, when compared to “traditional” wireless microphone systems.

It is my understanding that when the DTV transition became imminent, Audio-Technica decided to investigate alternatives to standard systems based on UHF frequencies.

Only Sabine, X2, RevoLabs, and some of Lectrosonics’ more specialized products have gone out of the standard TV band in recent years, with products in the ISM (902-928MHz), 1.9 GHz and 2.4 GHz ranges.

System Basics
The SpectraPulse system is made up of the following main components:  drm141 antenna/digital receiver module, aci707 audio control interface, mtu101 boundary microphone/transmitter, and the mtu201 desk stand/transmitter that can be used with gooseneck microphones.

There is also a charging station for up to seven transmitters and an optional software package to add data encryption to the system.

The drm141 antenna/receiver unit is usually mounted on the wall in the conference room, and then connected to the aci707 control interface via a standard shielded CAT5 cable.

Technology
In contrast to all these other offerings, SpectraPulse operates with a center frequency of 6.35 GHz and a bandwidth of 500 MHz, and thus has an UWB (Ultra Wide Band) designation. UWB is a “carrier free” wireless method, while even spread spectrum still relies upon a carrier, which, if disrupted, means that signal will be lost.

There are some advantages to operating at such a high frequency – most importantly; there are no TV or other wireless microphone transmissions in the range.

In addition, the SpectraPulse design involves the use of very rapidly pulsed signals, each one a short burst over a very wide instantaneous bandwidth of frequencies. While the technology concept is by no means new (it dates back to Marconi in the late 1800s), A-T is the first to implement it with a commercially viable product.

In the course of writing this article, I also received some additional input from Jackie Green, Vice President of R&D/Engineering at Audio-Technica, who notes that the 6 GHz band was targeted because it’s one of the most “open” ranges of spectrum.

A look at the FCC web site shows only fixed communications, fixed satellite communications and mobile communications operating in the area of 5.925 - 7.075 GHz.

Jackie also notes, “We have eliminated most possible conflicting frequency applications by being centered at 6.350 GHz, and in addition, even if we operate a SpectraPulse system physically next to the broadcast satellite up and down links (not random, but specific fixed frequencies between 4 GHz and 6.425 GHz), we do not experience interference or degradation of our signals.

“This is because SpectraPulse is not a carrier-based technology. There is no signal to ‘mix’ or ‘fade’ or ‘drop.’ If a competing wireless system comes in on exactly our frequency of operation at exactly our point in time (very unlikely) it’s not that our system won’t work - the problem is that the DRM (Digital Receiver Module) simply cannot decide which signal is the one it wants in the TDMA (Time Division Multiple Access) time slot ,and starts bouncing back and forth between signals in time or experiencing collisions. This sounds like talking through a ‘fan,’ but it doesn’t sound like a hit, drop, pop, fade, or disappear entirely, as users experience with traditional FM signals.”

Specifications
The SpectraPulse system supports the use of up to 14 channels in one location, which is more than enough for most conferences. It appears to be designed around two seven-channel blocks, in that the aci707 supports seven channels.

Audio frequency response is 100 Hz – 12 kHz, plenty for speech applications but not optimum for full-range program material.

But again, the system is designed for conference applications rather than for theater or live music, and by eliminating the need for a compander, audio quality is comparable to traditional FM systems.

Range is quoted as up to 75 feet, which is more than enough in this application.

Here’s an interesting specification: the average RF output from the transmitters is 40 nanowatts. This is several orders of magnitude less than the typical analog FM or even digital modulation systems that have outputs in the range of 10 to 100 milliwatts.

Part of the key to understanding the A-T spec is that this is the average of a pulsed system. The peak output of any pulse is undoubtedly much higher than this but only for a very short duration (2 ns).

A/D and D/A conversion are 16 bit, and overall latency is an impressively low 1.1 ms. Normally, this would indicate a high sample rate, but in this case, the sample rate is 24 kHz, thus the audio frequency response extending “only” to 12 kHz.

The link between transmitters and receiver is bi-directional, allowing for muting if synch is lost, and reacquisition occurs in only 3 ms after sync loss.

Data encryption is offered as an optional feature by adding the sep128 software package. AES – Level 3 standard 128-bit encryption gives this system the edge over some other digital wireless products. If you need data security, this is a very robust way to go.

Cost
I found that the mtu101 transmitter has a street price of about $890, which is right in there with what AKG and Lectrosonics offer for digital transmitters. The drm141 antenna/receiver seems to have a street price of about $8,600, which seems expensive until you consider that it can work with up to 14 channels – about $615 per channel.

The aci707 carries a price of about $4,600 and handles up to seven channels, or about $660 per channel. All in all, if you were to purchase a complete 14-channel system, this works out to about $2,100 per channel. This is not inexpensive, but there are several systems that cost significantly more.

Conclusions
All in all, this is a very impressive piece of technology and shows that Audio-Technica has vision and was willing to take a substantial risk with large R&D project outside the “normal” realm of wireless microphones.

The result really shows promise, particularly for installed applications where very long range is not needed, but data security, ease of setup and basically invisible operation are required.

It will be interesting to see if A-T is able to refine this technology even further to provide products applicable for use in touring, theater, and other types of productions.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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More posts by Mike Wireless:
Latest Wireless Series #5: Inside The Shure UHF-R Wireless System
Latest Wireless Series #4: Inside the Sennheiser 2000 Series
Latest Wireless Series #3: Inside The Lectrosonics D4
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700

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Tuesday, November 03, 2009

From The Recent AES Panel Session: “Practical Advice for Wireless Microphone Users”

Veteran panel addresses key wireless and RF issues for "typical" users

During the recent AES Convention in New York, I attended a panel discussion entitled “Practical Advice for Wireless Microphone Users,” chaired by James Stoffo.

The panel included representatives of three top wireless microphone system manufacturers, including Joe Ciaudelli of Sennheiser, Karl Winkler of Lectrosonics, and Douglas Totel of Shure.

Stoffo has previously chaired panel discussions at AES that concentrated on large-scale wireless mic installations and applications such as the Super Bowl, but this year the focus was on the “typical” wireless user -  a good move.

The discussion began with a look at determining operational requirements and expectations, such as how many channels might be needed, the form factor of transmitters, RF power, etc.

Some smart comments were offered by the panelists about providing a reality check to potential clients or customers about their expectations, with Ciaudelli making the point that “if it doesn’t need to be wireless, use a hard line” in addressing an example of a drummer requesting an in-ear system.

Focus then shifted to antenna types, including dipole and directional types, with Stoffo also noting helical antennas can help in avoiding the problem of antenna orientation, since performers tend to move around and hold transmitters in various positions.

The designs of Sennheiser and Professional Wireless Systems (PWS) helical antennas were compared, with a general conclusion that the Sennheiser unit is better suited for wider coverage applications while the PWS unit is better suited for longer range applications due to it’s narrower angle of coverage.

The need, or not, for RF amplifiers and/or amplified antennas was also covered, with the clear point made that boosters are needed only to overcome long cable runs rather than to “get a stronger signal”.

Coaxial cable loss was discussed in this context as well, with the recommendation to lean toward low-loss coax cables like RG213 and 9913F. It was also recommended to keep IEM transmitter antennas as far away as possible from rack receiver antennas to avoid overloading the receivers.

Of course, frequency coordination and band planning were on the docket as well, and specifically, preparation for multiple channels of wireless systems. Frequency coordination techniques mentioned include having pre-calculated backup frequencies at the ready. Totel showed an example of band planning where there was no overlap between IFB, IEM, beltpack and handheld groups.

Winkler also brought up the importance of proper audio gain staging to achieve optimum results, not only to keep the audio optimized but also because wireless mic transmitters need a healthy signal in order to modulate the RF carrier to get a good signal at the receiver.

Some of the tools available for wireless mic planning, including spectrum analyzers of various cost ranges, software tools, and resource web sites were covered.

The summary statements from each of the panelists centered on a common theme: planning is key to success, and having backup frequencies and other fallback plans help prevent problems.

I enjoyed the panel’s discussion, and the 60 or so in the audience appeared appreciative. In fact, many of them stayed afterward to ask further questions.

It looks like AES has found a good formula and excellent panelists for this topic, and I hope to see them continue with it in years to come.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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More posts by Mike Wireless:
Summary Of Spectrum Changes For Church Sound Wireless Users
Upcoming AES Presents Opportunities To Learn More About Wireless
Latest Wireless Series #5: Inside The Shure UHF-R Series
The Myths of Wireless System Transmitter Power
Latest Wireless Series #4: Inside the Sennheiser 2000 Series
The RF Spectrum Before & After The “Big Day”
Latest Wireless Series #3: Inside The Lectrosonics D4
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Wednesday, August 26, 2009

Two New Developments Emerge Under The “White Spaces” Heading

Microsoft enters the fray; and is a new "post white spaces" wireless company entering the market?

Two interesting developments have emerged recently under the heading of “white spaces”.

First, if you recall, the FCC authorized the development and eventual marketing of “white space devices” that have now come to be known as TVBDs (TV Band Devices).

However, the technical requirements for these devices are quite stringent; specifically, that they must sense other signals and take a lower priority in any given location than existing TV broadcasts and wireless microphones.

Microsoft, working with researchers at Harvard University, has announced that it has set forth protocols for networks that will use this “unlicensed spectrum”.

Wireless microphones pose a significant challenge to such devices and networks because they’re very low power, and also, are only on when they’re being used.

To deal with this, Microsoft’s approach includes an algorithm that detects available frequencies and switches to a backup channel if interference is detected.

In tests, the device has detected interference from a wireless microphone and moved to another frequency within three seconds.

Three seconds? That can be an eternity if you are experiencing a wireless system dropout, but it depends on the situation as to whether or not it would be a problem.

For instance, what if you turn on all the wireless transmitters for a particular scene in a stage production?

In that scenario, the TVBD or local network would recognize these transmissions and avoid them with plenty of time before the wireless mics would actually be used.

On the other hand, imagine there’s a person in the lobby of a theater, uploading a file to a network from his TVBD. Then, he walks into the theater in the middle of an ongoing performance, where his TVBD starts to interfere with a wireless mic channel being used for the show.

In this case, there might actually be a wireless mic dropout that would last a full three seconds.

Of course, this assumes that the signals did not interfere with each other from the lobby, but would do so the instant they were in the house together.

It seems that there is still major room for improvement before these devices are ready for prime time.

Second, a company called RF Venue has emerged, promising to “Refine Wireless Microphone Performance in the White Space Era”.

It’s not clear if this company offers hardware, software, system management or some combination of these elements. What is clear is that this may be the first new company to enter the market, post-white spaces.

Existing wireless microphone manufacturers have all done their part to increase reliability of their systems in light of re-allocated spectrum and the threat that there may be new, unlicensed devices sharing spectrum.

But I think we will see more of these new entries as the issue heats up. That is, along with more new entries from existing players.

The next couple of years ought to be very interesting indeed.

Related links:
http://www.telecommagazine.com/newsglobe/article.asp?HH_ID=AR_5577
http://www.rfvenue.com

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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.

More posts by Mike Wireless:
Upcoming AES Presents Opportunities To Learn More About Wireless
Latest Wireless Series #5: Inside The Shure UHF-R Series
The Myths of Wireless System Transmitter Power
Latest Wireless Series #4: Inside the Sennheiser 2000 Series
The RF Spectrum Before & After The “Big Day”
Latest Wireless Series #3: Inside The Lectrosonics D4
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Monday, August 17, 2009

Upcoming AES Convention Presents Great Opportunities To Learn More About Wireless

Two changes to learn about wireless from industry leaders, both at one location

Just a quick note to point out that there will be two wireless microphone-related panel discussions at the upcoming Audio Engineering Society convention to be held at the Javits Center in New York this October.

The AES convention, which is held annually in the U.S. on alternating coasts, always has a number of excellent workshops and panels covering sound reinforcement, and this year, must-see subjects such as “AC Power and Grounding”, “Microphone Dressing” and “Church and House of Worship”, among others, will be part of the live sound menu.

The wireless programming in particular should be excellent.

On Saturday, October 10 at 2 pm, Henry Cohen of Production Radio Rentals will chair a panel to discuss the issues of White Space and Spectrum Allocation. For those of you who don’t know Mr. Cohen, he is a guru in the area of wireless microphones, radio transmission and RF spectrum.

I strongly advise you to attend this panel discussion if you can – you’ll end up better informed on this important issue.

In the same room, starting at 3 pm, following the White Spaces panel, James Stoffo of Professional Wireless Systems will chair a panel titled “Practical Advice for Wireless Microphone Users”.

Mr. Soffo has vast experience with wireless microphone systems, large and small – he has coordinated RF frequencies for the Super Bowl and the Grammys, to name just a few.

This is the panel to attend if you are using or plan to use wireless microphones, period. Issues covered will include antenna choice and placement, component choice, gain staging and common pitfalls.

Even if you think you know a lot about wireless microphones, Mr. Stoffo and his panelists will give you some important clues about how to increase your knowledge and improve your results on stage, in your church, on your tour, or in your band.

Click here for more information.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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.

More posts by Mike Wireless:
Latest Wireless Series #5: Inside The Shure UHF-R Series
The Myths of Wireless System Transmitter Power
Latest Wireless Series #4: Inside the Sennheiser 2000 Series
The RF Spectrum Before & After The “Big Day”
Latest Wireless Series #3: Inside The Lectrosonics D4
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Friday, August 07, 2009

Recent Wireless Technology Series: Shure UHF-R Series

This is the latest installment in a series detailing the latest technology in wireless microphone systems. Click to read the other installments: AKG DMS 700; MIPRO ACT Digital; Lectrosonics D4; and Sennheiser 2000 Series.

The Shure UHF-R currently reigns as the most widely rented and specified wireless microphone system.

It’s been on the market for four years and has garnered legions of fans.

Let’s look at some of the features and technical specifications that make the UHF-R system tick.

Components
Receiver options include the single-channel UR4S and the dual-channel UR4D. Most often seen, of course, is the dual-channel variant.

Three transmitters are available, including the UR1 standard bodypack, UR1M micro bodypack and UR2 handheld.

The bodypack units are connected to lavaliere and headworn microphones via a TA4, and in the case of the smaller UR1M, a 3-pin Lemo can be ordered as an option.

The handheld transmitter can be outfitted with a wide variety of Shure mic capsules, ranging from the SM58 to the SM86 to the high-end KSM9.

This is indeed arguably one of the stronger aspects of this series – the direct compatibility with Shure’s industry-standard range of capsules.

The handheld transmitter is available in standard black finish as well as the more “sexy” satin nickel. In the past few years, the old rule that “microphones must be black” (otherwise they might reflect light into TV cameras and/or be noticed by the audience) has abated, so this additional finish option fits right in with the current preference of options. 

Technical
The UHF-R system employs Shure’s proprietary and patented Audio Reference Compander system.

Audio companding is a “necessary evil” in any analog wireless system, because otherwise there’s not enough dynamic range available in the link to provide an appropriate full-range musical signal.

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The Shure approach is very well regarded by engineers and artists alike for its natural sound quality. Dynamic range is specified as >105 dB, A-weighted, which is quite good - better than CD, in fact. Most high-quality wireless systems today have a similar specification for dynamic range.

Overall frequency response of the system is listed as 40 Hz -18 kHz +1, -3 dB. That’s a good specification and compares well to other high-quality analog systems.

In contrast, digital and digital hybrid systems extend a bit lower and a bit higher, with overall flatter response.

Nonetheless, the audio range of the UHF-R is more than enough to satisfy the demands of touring and installed sound markets, as evidenced by the high level of acceptance.

Transmitters in the UHF-R line allow for two different RF power settings, which I mentioned in an earlier post is something we’re seeing more.

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For the U.S. market, the UR1 bodypack transmitter can be switched between 10 mW and 100 mW.  The UR1M microbodypack and the UR2 handheld can be switched between 10 mW and 50 mW. 

For Europe, the handhelds and bodypacks all offer selectivity between 10 mW and 50 mW, to satisfy different regulations. The basic idea behind switchable power is that the user can choose between “low battery consumption” and “long range”.

The different in range between 10 mW and 100 mW (a 10 dB difference in power) is about 50 to 60 percent, which can be significant depending on the application.

And, of course, with all questions of range there are a vast number of external factors involved as well. I plan to get into this topic in more detail in a separate post – stay tuned.

The frequency ranges offered in the UHF-R package cover the entire available spectrum.

The G1 range covers the very low end of the available UHF spectrum, from 470 MHz - 530 MHz, followed by the H4 range from 518 MHz - 578 MHz.

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Note that these two ranges overlap a bit - a nice feature in some cases, but users should be aware that it is possible to have a transmitter at the top end of G1 step on one at the bottom of H4.

The J5 covers 578 MHz - 638 MHz and the L3 range covers 638 MHz - 698 MHz (the top of the current legal UHF range for wireless microphones in the U.S.). The system is also available in bands for Europe, Japan and Korea, among others.

Note that each of the U.S. ranges covers a fairly wide 60 MHz and provides nearly 2,400 frequencies in 25 kHz steps. The frequency ranges for Europe tune as wide as 75 MHz.

Networking
The UHF-R system was among the first to include complete networking capability, which greatly enhances the ability to quickly coordinate all frequencies and implement them throughout the receivers and transmitters.

Other companies have followed suit: Sennheiser with the Net1 system, and more recently, the 2000 Series; AKG with the DMS700, and Audio Technica.

Most, if not all, professional wireless systems will have these features within a few more years, but Shure was very wise to take such a comprehensive approach early.

Pricing
The UR4D receiver typically sells for about $2,800, while the standard beltpack transmitters are about $800 and handheld transmitters range from about $900 to about $1,800, depending on the capsule chosen.

These prices compare directly to the Sennheiser 2000 Series (see previous post) and thus are in the “upper middle” range. The Sennheiser 3000 and 5000 Series systems are considerably more expensive, while the Lectrosonics 400 Series and AKG 700 are somewhat less expensive.

Conclusion
It is obvious that the UHF-R system from Shure is well thought-out, with an excellent set of features and with a high level of quality that satisfies professional customers in many markets.

Shure did its homework when designing this system and it has paid off, and most certainly will continue to do so.

Find out more about the Shure UHF-R Series here.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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.

More posts by Mike Wireless:
The Myths of Wireless System Transmitter Power
Latest Wireless Series #4: Inside the Sennheiser 2000 Series
The RF Spectrum Before & After The “Big Day”
Latest Wireless Series #3: Inside The Lectrosonics D4
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Monday, July 20, 2009

Recent Wireless Technology Series: Sennheiser 2000 Series

This is the fourth in a series detailing the latest technology in wireless microphone systems. Click to read the other installments: AKG DMS 700; MIPRO ACT Digital; and Lectrosonics D4.

Sennheiser has long been one of the top wireless system manufacturers, respected for solid technology, high audio quality and a wide range of products, all evidenced by a long and varied user list.

Earlier this year at the NAB (National Association of Broadcasters) show in Las Vegas, Sennheiser introduced the 2000 Series, its latest wireless system development.

Pricing of the new 2000 Series is in line with the Shure UHF-R Series, and it now represents the “middle” of the Sennheiser line, with the 5000 and 3000 Series at the top, followed by the 2000 Series, and then the evolution Series, and finally, the Freeport system that’s primarily marketed in MI stores.

Components
The 2000 Series lineup includes the following transmitters: SK 2000 belt pack, SKP 2000 plug-on, SKM 2000 handheld, SR 2000 in-ear monitoring (IEM) and SR 2050 dual IEM unit.

Receiver choices are comprised of EM 2000 single-channel rack unit, EM 2050 dual-channel rack unit, and EK 2000 camera mount unit, and the EK 2000 IEM beltpack receiver.

Additionally, each generation of evolution wireless is compatible with the 2000 Series line, as are capsules and accessories.

Technology
The EM 2050, likely to be the standard receiver in the 2000 Series, provides up to 75 MHz switching bandwidth and 3,000 frequencies to choose from, with 25 kHz steps. This is compared to 36 MHz with 1,440 frequencies for the popular evolution G2 Series and 42 MHz with 1,680 frequencies in the newer G3 Series.

Therefore, the 2000 Series offers quite a wide tuning range and plenty of frequencies to choose from, which can be a real advantage in today’s challenging and changing RF environment.

All 2000 Series transmitters (U.S. models only) offer switchable RF output power levels at 10, 30, 50 and 100 mW, to better meet the needs of different applications.

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This is a nice feature, and it’s beginning to become more common.

One of the main features in the 2000 Series is the Ethernet port and WSM software – both used for system management, monitoring and control.

They offer the user quick access to all system parameters and conditions, along with the ability to quickly implement an entire frequency plan.

Interestingly, even as we see more digital and “hybrid” wireless systems coming into the market, the 2000 Series utilizes Sennheiser’s HDX analog companding technology that was introduced about 10 years ago with the evolution G1 Series. Don’t get me wrong, though, because this is not a detriment.

The primary advantage of analog companding is that it avoids any latency – all digital or hybrid systems incur some signal delay, due mostly to the A/D conversion process.

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A disadvantage is some signal degradation, particularly with certain types of source material - high-frequency transients are particularly challenging for companders.

Nevertheless, HDX technology has pleased many users and no doubt will continue to do so.

Features
Like many other comprehensive wireless microphone systems, the 2000 Series allows for synchronization of the transmitters via an IR port on the receivers.

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This certainly speeds setup when compared to manually transferring frequencies.

The 2000 Series rack-mount receivers can also be daisy chained up to 16 channels without the need for external antenna distribution. 

One additional nice feature on the EK 2000 portable receiver for video users is the addition of diversity (a change from the evolution G2 EK 100, 300 and 500). This should provide greater range and resistance to dropouts.

Also, the EK 2000 portable receiver offers synchronization of the transmitters via an IR port, a very convenient feature for on the go frequency coordination.

Finally, the SK 2000 body pack transmitters use the Lemo 3 connector, shared by Sennheiser’s SK 3063, SK 50, SK 5012, etc.

Thus, if you have lav mics already wired for these upper-tier transmitters, you can use them directly with the new 2000 Series bodypack. 

A unique feature with the SK 2000 for guitarists is a built in guitar tuner and a virtual cable emulation that gives the user the opportunity to select a preferable impedance.

Pricing
As noted earlier, the 2000 Series is priced similarly to the Shure UHF-R Series – this probably isn’t an accident. The EM 2050 receiver can be found for a street price of $2,798, while the bodypack and handheld transmitters run at just under $800 each.

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This equates to a per-channel price (if counted in multiples of two) of about $2,200.

Conclusions
While certainly not the most expensive system out there, the 2000 Series is a serious investment when compared to the evolution Series as well as models from Audio-Technica, Lectrosonics and the aforementioned Shure.

Yet the fact remains that the 2000 Series offers a number of very nice features – particularly the stuff that makes the user’s job of setup and monitoring easy and quick. Sennheiser retains its place among the leaders of wireless technology, and the 2000 Series should make a lot of pro users (with pro budgets) happy.

Find out more about the Sennheiser 2000 Series here.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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.

More posts by Mike Wireless:
The RF Spectrum Before & After The “Big Day”
Latest Wireless Series #3: Inside The Lectrosonics D4
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Tuesday, June 30, 2009

The RF Spectrum Before & After The “Big Day”

A look at the spectrum between 500 MHz and 700 MHz

So the big day (June 12, formerly February 17, 2009) came and went, and now we have the results of “the change”.

For those of you living under a rock for the past 10 years, what has happened is that full-power analog TV broadcasts have ceased in most US markets.

At the same time, most of the of spectrum between 698 and 806 MHz, formerly used by TV broadcasts and wireless microphones, now has new owners and is not populated by TV broadcasts any longer.

The legal status of wireless microphone systems in the 700 MHz band is not entirely clear, but the FCC’s intentions appear to be that wireless mics will not be allowed here.

So let’s look at the spectrum between 500 MHz and 700 MHz, covering most what is now available to DTV broadcasts and Part 74 users, including wireless microphone systems.

The first/top image (below) shows this range before the transition, and the second/bottom image (also below) shows the same spectrum after June 12. It is evident that almost all analog sources have disappeared, while only DTV sources remain.

What about using wireless microphone systems in the 700 MHz band?

First, you may still have systems in the 700 MHz band that will continue to operate, until such time as a new, strong signal comes along and interferes.

For many, this may be the right approach: use your equipment until it no longer works. However, keep your eyes open for any announcements about the likely FCC ruling rendering such systems actually illegal.

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Currently, there are few signals in that range, but there are some, and soon there will be more.

For those of us using systems between 470 and 698 MHz, our lives should actually be a bit easier for a while. The spectrum is more open, and we should not see the kinds of rapid changes we have seen over the past couple of years.

DTV transmissions are still being optimized, and broadcasters are recommending that people “do a new scan for channels once a month”. I would suggest the same thing for your wireless microphone systems, to insure that you are steering clear of any potential interference. (But you were doing that already, right?)

As to what will become of the remaining usable spectrum, it’s too early to tell. But as TVBD (TV Band Devices) begin to appear, we’ll certainly learn more.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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.

More posts on PSW by Mike Wireless:
Latest Wireless Series #3: Inside The Lectrosonics D4
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

Also check out:
Basic & Essential: What You Need To Know About Wireless Systems (A Primer)

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Tuesday, June 23, 2009

Recent Wireless Technology Series: Inside The Lectrosonics D4

This is the third in a series detailing the latest technology in wireless microphone systems. Click here to go directly to the first installment (AKG DMS 700) and click here to go to the second installment (MIPRO ACT Digital).

The newest wireless system offering from Lectrosonics, the D4, is the first one I’m reviewing that does not use the UHF spectrum.

Instead, the D4 runs in the license-free ISM band between 902 and 928 MHz. Unlike the UHF band, this slice of spectrum is only 26 MHz wide (as opposed to over 230 MHz for UHF).

The FCC considers the ISM band to be license free, but still puts restrictions in place on how much power transmitters can have and how much bandwidth they can occupy.

However, the rules are very different than for wireless mics operating in the UHF band.

Beyond the differences in operating frequency between the D4 and the previously reviewed offerings, this system is completely different in form factor as well.

Basics
The Lectrosonics D4 System consists of only two units: the D4T transmitter and the D4R receiver. Each of the units looks roughly the same, and are exactly the same size – about 4 inches by 4 inches by 2 inches.

Obviously, this transmitter is not designed to be worn on someone’s person, but instead used as a “base station” of some kind.

he receiver is roughly the same size as many camera-mount “portable” types, being much smaller than a rack-mount receiver but certainly larger than the really small receivers from Sennheiser and Lectrosonics.

The most important feature of the D4 is probably the multi-channel capability, being that the system shuttles four channels over a single carrier.

The system uses digital modulation (like the AKG DMS700 and MIPRO ACT Digital) but according to the specifications, the occupied bandwidth is 2 MHz (!) vs. a more typical 100 to 200 kHz for most wireless systems.

Again, this is because in the UHF band, the FCC specifies that transmitters must fit into a fairly narrow piece of spectrum, and the rules are different in the ISM band.

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And being that this spectrum is license free, this means that other types of systems may be operating there, depending on your location. Wireless DMX for lighting, as an example, also uses this band.

The wide occupied bandwidth also means that the number of channels (RF carriers) that can operate simultaneously is limited. As it turns out, the D4 offers four operating channels.

Thus, in theory up to 16 audio channels can be transmitted in the band.

The transmitter and receiver in the D4 system each have four mini XLR 3-pin jacks for connecting external devices.

The transmitter accepts line level or AES/EBU inputs, and the receiver outputs either line level or AES/EBU outputs.

So it seems that this is truly not a “wireless microphone” system, but more of a “wireless snake”.

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Specs
The audio performance claimed by this system is impressive: 20 Hz to 20 kHz (±0.5dB), which is superior to even some of the other “pure digital” offerings. Sample rate is 48 kHz and A/D, D/A is at 24 bits.

Latency is claimed as “less than 1 ms for digital in/digital out and 2.2 ms for analog in/analog out”. Signal to noise is 103 dB, A-weighted, which seems a bit low compared to some of the other offerings.

But what is it for?

The aim seems to be for this to be the equivalent of a four-channel snake. Range is claimed as “up to 1,200 feet” but of course as we all know, external factors play the largest role in the range of wireless systems like this.

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Still, this is good range and should be useful in certain applications. Perhaps this system can be used for monitor returns or some other type of signal from one place in the venue to another?

Because Lectrosonics is most well known in the film and broadcast markets, perhaps they are expecting this will be used as a camera hop system between a production mixer and one or more cameras.

I suppose time will tell.

Cost
U.S. list price for the D4 is $2,500 for the transmitter, and $2,500 for the receiver, or $5,000 for the system. I suspect street prices are closer to $4,000 for the system.

This is pretty expensive, but compares favorably to four channels of any other pro wireless system. It does offer some unique features but it is not as flexible as typical single-channel systems.

Conclusion
This is an interesting offering from Lectrosonics although it does not at all fit in the mold of what is offered by other manufacturers. Only Zaxcom has similar wireless products.

One thing’s for sure: It will be interesting to see how such new developments play out in the live sound industry.

Find out more about the Lectrosonics D4 here.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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More posts by Mike Wireless:
Latest Wireless Series #2: Inside The MIPRO ACT Digital
Latest Wireless Series #1: Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Wednesday, June 10, 2009

Recent Wireless Technology Series: Inside The MIPRO ACT Digital

This is the second in a series detailing the latest technology in wireless microphone systems. To read the first installment, covering the AKG DMS 700 system, click here.

The MIPRO ACT Digital wireless system has been on the market for a couple of years, and like the AKG DMS 700 digital wireless system, it uses the same UHF bandwidth we’re all familiar with when using any UHF-band microphones.

(Note that the “D” in “Digital” for this MIPRO system is capitalized because it is part of the official product name, rather than the generic system name.)

Specifically, the MIPRO ACT Digital covers 620–692 MHz – fairly close to the upper limit of what the FCC Part 74 rules now allow for this type of use.

In terms of features and operation, it’s somewhat similar to the Lectrosonics 700 Series digital wireless system, but with some interesting differences.

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Basics
Two receivers are offered in the ACT Digital system – ACT-81 single-channel and ACT-82 dual-channel, both single-rack-space units.

Both the companion ACT-8H handheld transmitter and ACT-8T beltpack transmitter feature charging contacts – a nice convenience, but note that these transmitters only operate using rechargeable battery packs.

The rechargeable approach is usually just fine for churches or other installed sound applications, but sometimes it’s not as popular for touring or portable music application, where the convenience of “getting some new/fresh AA batteries from the corner shop” is more ingrained.

Although the bandwidth of this system is indicated as “620–692 MHz,” it’s actually broken into three fixed bands, each 24 MHz wide.

Each receiver and transmitter can only tune within its specified range. This is similar to many other systems, such as those from Zaxcom, Lectrosonics, Sennheiser evolution, etc.

Most analog systems introduced in the past few years, however, such as the Sennheiser 2000 Series and Shure UHF-R, have much wider bandwidths, with 70 MHz or even 90 MHz being quite common.

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The AKG DMS 700 offers a whopping 155 MHz, which is not matched by any other system at this time. The trade-off is that the wider the bandwidth, the more unwanted signals are being “digested” by the receiver front end. In general, users should choose the narrowest bandwidth that still meets their needs.

Like the AKG system, the MIPRO offers digital outputs and a word clock connection - nice features now that consoles are more and more accepting digital sources. Again like the DMS 700 (as well as Sennheiser 2000 Series and Shure UHF-R and ULX Pro), the ACT Digital has an IR port for synchronizing the settings between the receiver and the transmitter. This can be a nice, time-saving feature.

The color display on the receiver front panel is a good feature that is hampered by a limited interface. A single knob to change all settings?

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The product documentation is also quite limited – while the company’s marketing literature is fairly clear, the owner’s manual is truncated, lacking in detail.

Audio Performance
The ACT Digital system uses a sample rate of 44.1 kHz and a 24-bit A/D conversion process. This yields a flat frequency response of 20 – 20 kHz with a tolerance of -2 dB, better than most analog wireless systems, particularly at the bottom end. Most analog systems exhibit something like a 40 or 50 Hz low end response and a 16 or maybe 18 kHz on the top end.

Because the ACT-Digital system does not use a compandor, the associated artifacts are gone as well. The dynamic range of this system is a very nice 110 dB, A-weighted.

Latency or “group delay” for the system is listed at 4 milliseconds (ms), which is on the order of many other types of digital signal processing, including consoles, and is largely a factor of the 44.1 kHz sample rate.

Higher sample rates would yield a lower latency, but would also require a greater data rate between transmitter and receiver. While 4 ms is respectably low, it is bested by some other systems. And for speech applications, it is well within the range that will be undetectable. 

The only problem might be if this system were used with a digital console along with any additional analog processing.

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The resulting latency might be in the 8 to 10 ms range – within the area of detectability for many users, particularly singers using in-ear monitoring (IEM) systems.

Encryption
The ACT Digital offers selectable encryption at a 128-bit key length, now the minimum for any truly secure system and relatively “sell-able” – although it is restricted as to who can buy it, there is no special government license needed as there is for 256-bit encrypted systems. Also, 128-bit can be very robust if implemented properly.

Choosing to engage the encryption on this system is a simple as selecting it on the receiver and on the transmitter. This is a very easy-to-use feature on the ACT digital wireless.

Conclusions
While there aren’t any real ground-breaking features or technology here, the ACT Digital wireless system is a nice package and can certainly provide quality audio and data encryption where needed.

Keep in mind that it competes with other signals in the UHF band, and offers only three 24 MHz bands within the larger tuning range of 620-692 MHz, so whether or not this system will work well in larger, multi-channel applications and with competing signals (potential interference) in the same band needs to be tested.

Most digital wireless system manufacturers claim that their products are “impervious to inter-modulation problems” and “not affected by crowded RF spectrum”. But since there are no known larger-scale systems out there, this remains to be seen

The audio specifications look very solid and are indicative of what can be done with digital as opposed to analog with respect to wireless systems. The latency is fairly low and should not affect most applications. Other comparable systems include the Lectrosonics 700 Series and the AKG DMS 700.

U.S. MSRP of MIPRO ACT Digital: $3,520 for the dual-channel receiver, $1,800 for the single-channel receiver, $2,000 for the handheld transmitter, and $1,920 for the belt-pack unit.

Note that this is nearly double the listed pricing for that AKG DMS 700, and is in the ballpark of the pricing for the Lectrosonics 700 Series. Therefore - and as always should be the case - only you can decide if the feature set, audio quality and other factors make this the right product for you.

Find out more about the MIPRO ACT Digital system here.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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Other posts by Mike Wireless:
Inside The AKG DMS 700
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Thursday, June 04, 2009

Recent Wireless Technology Series: Inside The AKG DMS 700

This is the first in a series detailing some of the latest technology in wireless microphone systems.

A number of manufacturers have introduced new wireless microphone systems in the past two years – many of them in response to the changes in the RF spectrum brought about by the FCC.

As a result, I thought it would be interesting to provide an in-depth look at a number of these recently introduced systems, beginning here with the AKG DMS 700 digital wireless system, which was announced at NAMM in January of this year.

Professional caliber digital wireless systems have been on the market for several years, as evidenced by offerings from Telex, Zaxcom, and Lectrosonics (to name a few off the top of my head). Mipro also introduced a digital system within the past couple of years, and the Sennheiser Digital 1000 system was introduced way back around the year 2000, although I guess some might argue that it’s not a true “pro” system.

AKG’s effort with digital wireless with the more recent DMS 700 provides users with some important advancements and merits a detailed look.

The Basics
The DMS 700 consists of three main products: a handheld transmitter, a bodypack transmitter, and the dual-channel rack-mount receiver.

Interestingly, this system is designed to operate in the standard UHF spectrum, covering two ranges - between 548 MHz and 698 MHz for the U.S. and other markets where this range is legal; and between 710 MHz and 865 MHz for Europe or other markets where this range is legal.

The first thing to note is that DMS 700 covers a very wide range of 155 MHz – most UHF systems cover somewhere between 25 MHz and 90 MHz per unit. This very wide tuning range allows up to 100 channels to be in use simultaneously.

Usually, there’s a trade-off between how wide of a band is covered and noise from the PLL (phase locked loop). But in theory, a digital system would not suffer from this noise issue.

That said, the DMS 700 is still an RF device, and thus 155 MHz is a lot of UHF spectrum, with a lot of high-energy sources (NTSC/PAL and DTV broadcasts). Yet because this system is digital, it’s modulation scheme will discriminate between “good” and “bad” data, and/or unwanted data.

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Even further along these lines, the receiver comes with an “Environment Scan” function that converts it into a spectrum analyzer. It searches the receiver’s entire frequency band for active radio frequencies and shows them in a frequency spectrum graph on the front panel display.

Specs
Several of the specifications for the DMS 700 are impressive, while others are standard for high-quality wireless. Audio frequency response is specified as 25 Hz to 20 kHz, ±3 dB, which is only matched by other digital or “digital hybrid” systems.

One problem with any analog-based frequency-agile wireless system is that the PLL does not allow for frequencies below about 20 Hz to pass, otherwise the PLL itself will “unlock” and the system will become unusable until power cycled.

Thus, typically a high-pass filter is installed to cut the audio below say 40 or 50 Hz. So to have flat response down to 25 Hz is the domain of digital-only systems.

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The inclusion of AES-3 digital outputs on the DSR 700 receiver is something we’re starting to see (also found in Sennheiser’s EM3732 receiver, although it is an analog system with an A to D converter and DSP-based compander) and should be a nice way to interface with digital consoles.

By connecting via the digital outputs, the DSR 700 exhibits 120 dB signal-to-noise, which is impressive.

Another feature that is appearing on the horizon for receivers is the Ethernet connection so that control of the receiver can be executed as part of a PC network. Sennheiser and Shure have started doing this as well, and we can expect other manufacturers to follow suit.

The transmitters appear to be of standard size and shape from the outside, but also have some less commonly-seen features.

First, they offer switchable transmit power levels covering 10, 20, 30 and 50 mW. Although we’ve seen this in isolated cases before, usually in the form of “high and low power” like 10 mW and 50 mW, for instance, it’s nice to see a range of powers available on tap.

This also of course reflects that these products are planned for sale in a variety of countries where different power levels are specified by law. The U.S. allows 250 mW in the UHF band, but most of Europe allows just 50 mW while Japan and Korea allow only 10 mW.

Then there are market-specific needs, such as theater where power in the 20 to 50 mW range is desired due to the density of wireless channels in a small geographic area, such as the Broadway area of New York City.

RF power can also affect battery drain, so in cases where long battery life is needed, such as more rurally located churches where high power is not helpful, a 10 mW setting can be perfect.

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The DHT 700 handheld transmitter is available with a choice of either an AKG D 5 (dynamic) or C 5 (condenser) mic element; a wide range of AKG headworn, instrument, and lavalier microphones can be used with the DPT 700 bodypack transmitter.

One last feature that is only available to fully digital wireless systems is data encryption. Although systems from Lectrosonics and Telex have included encryption in their digital systems in the past, the inclusion of it in the DMS 700 makes this product available to a sector of the market usually reserved for specialized systems.

CostInterestingly, the cost of the DMS 700 is attractive in comparison with other top wireless systems. The handheld and belt pack transmitters both carry a U.S. MSRP of $999, and the receiver is $1,699 (again, U.S. MSRP). Thus a DMS 700 system with two transmitters has an MSRP of less than $3,700.

Conclusion
All in all, this appears to be quite an interesting system and should be a viable choice for many different applications. The cost aspect makes it even more attractive in terms of the sheer variety of features coupled with the level of performance offered by AKG in the DMS 700 system.

Find out more about the DMS 700 here.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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Other posts by Mike Wireless:
Is The UHF Spectrum Going To Ease Up After June 12?
Change The Only Constant In Marketplace For Wireless System Spectrum

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Wednesday, May 27, 2009

Darkness Before The Dawn? Is The UHF Spectrum Going To Ease Up After June 12?

Will it be like the heady days of the 1990s? Certainly not. But the good news is that things should lighten up a bit

One of the more common phone calls I’ve been receiving lately is from people looking for advice on which frequency bands to choose for their new wireless systems.

Maybe it’s all of the tours going out, or maybe people are finally getting the message about the spectrum changes and they want to “do the right thing”.

I’ve certainly noticed that quite a few systems proliferating the market in the last 10 years fall within the “700 MHz band” (between 698-806 MHz). I’d say that for many manufacturers, close to a third of what they’ve sold has been in this part of the spectrum. Sennheiser Evolution “C” range, Lectrosonics blocks 28 and 29, Audio Technica “E” range, for instance, all fall within the 700 MHz band. Some manufacturers have offered nothing but products in this range.

So here’s how these kinds of calls usually go:

Sound Guy: “So, we’re gearing up for our tour, and we already have vocal systems from Shure on J5, IEMs from Sennheiser in their B range, and a few other backline systems on a variety of ranges. We need to get some additional vocal wireless channels. What frequency band should we be looking at?”

Mike Wireless: “Well, you’ll need to squeeze in between what you already have since you’re covering everything from 518 to 650 MHz. Most manufacturers don’t offer much below 518 MHz. And some of the bands starting at 470 MHz can be problematic in large metro areas due to the public safety bands in that range.”

Sound Guy: “Wow, so what are we going to do?”

Mike Wireless: “You might want to consider consolidating all the backline stuff into one frequency band, and then look at something in the 490-518 range, then maybe something in the 650-698 range. That’s about all that’s left.”

SoundGuy: “OK, we’ll start there.”

Here’s the bottom line: with the analog TV stations still broadcasting, and DTV transmissions starting up or moving down below 700 MHz, the available UHF spectrum is more crowded than it’s ever been. Is there a light at the end of the tunnel? Maybe.

Come June 12, full-power analog TV broadcasts should cease, thus opening up some of the spectrum between 470 to 698 MHz.

Will it be like the heady days of the 1990s? Certainly not, because DTV signals take up a full 6 MHz where analog TV signals did not. And there are more channels overall now than there were 10 years ago.

But the good news is that things should lighten up a bit, and logically, we shouldn’t expect a whole slew of DTV channels to be added any time soon. The summer touring season should get a break, then.

That is, until the TVBD (TV Band Devices) start showing up. It’s difficult to predict how those might impact our use of wireless mics, but the main problem is that the signals will be transient rather than steady, so we may have to employ different techniques for scanning and coordinating wireless microphone frequencies.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

Previous posts by Mike Wireless:
Change The Only Constant In Marketplace For Wireless Spectrum

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Tuesday, April 28, 2009

Changes Are The Only Constant In The Marketplace For Wireless System Spectrum

Although we've all been aware of many aspects of these problems for several years now, it's important to note that this subject is a moving target

Many of us have heard about White Space Devices (WSDs) and that they have been named TV Band Devices (TVBDs) - maybe because “WSD” sounds a little too close to “WMD”.

And perhaps some of us are aware that according to the FCC, these devices will co-exist with our TV broadcasts AND our wireless microphones in the UHF band between about 500 and 698 MHz.

So of course the concern is that these devices might interfere with our wireless mics, and indeed, the potential is there for this to happen.

Fortunately, the FCC has built some protection into the technical requirements for TVBDs before they can be manufactured and sold. And the FCC has given wireless mics priority over TVBDs.

The problem of course is that ANY interference, no matter how brief, is unacceptable in the live production environment, so whatever protection is in these TVBDs absolutely must work and must not allow them to step on any wireless mic, anywhere.

One of the protections in place is that these devices are supposed to first access a database of known, registered wireless mics to see A) where they are and B) what frequencies they’re on. This database is supposed to be managed by a third party (in other words, not directly by the FCC).

This also means that wireless mic users would benefit from registering their products. However, thus far we’ve not seen an actual mechanism for this to occur.

But I did just run across something that may end up being involved:

http://www.showmywhitespace.com/ShowMyWhiteSpace/tabid/60/Default.aspx

This company, Spectrum Bridge, appears to be positioning themselves to be a marketplace for spectrum. How this will play out is not clear, but it may be worth signing up for their newsletter to keep informed.

I also found a cool feature:

http://whitespacemap.specex.com/

This is an interactive map showing the location of TV broadcasts all over the country. It appears that it may also in the future contain locations of registered wireless mic users or other spectrum users, and again, this might be something worth watching.

In the meantime, Shure has petitioned the FCC to delay allowing TVBDs into the market until they provide even greater protection for existing wireless mic users. (Read more about that here.)

Bravo to Shure for leading the way towards first getting the FCC to recognize the scope of the problem (there are millions of wireless mic users out there), and also for keeping up the fight on behalf of all who depend upon wireless systems.

We have a lot to lose if we suddenly have new devices stepping all over our wireless mics at churches, theaters, tours, boardrooms, stadiums, etc.

Although we’ve all been aware of many aspects of these problems for several years now, it’s important to note that this subject is a moving target and you (yes, you) need to stay informed.

This blog aims to help you do that.

Signing off for now…
Mike Wireless

Mike Wireless is the nom de plume of a long-time RF geek devoted to better entertainment wireless system practices the world over.

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