Zaxcom's Digital Wireless ENG Package

Zaxcom has been around for quite a while and has the distinction of engineering the first wireless mic system to use digital modulation. Digital modulation circumvents some of the side effects associated with the more commonly used FM transmitters, such as distortion due to companders, antenna diversity switching and RF interference.

Zaxcom has recently expanded their line for a wider range of applications. The ENG package goes far beyond supplying wireless microphone transmission. The components, used together, incorporate an IFB communication link, internal backup recording onto miniSD memory cards, and the ability to transmit and record in two-track stereo using a single body transmitter.


Fast Facts

Wireless audio connectivity for live or recorded ENG and other audio programming requirements

Key Features
Compact size, excellent frequency response, timecode capability

Suggested retail prices for the package components are: TRX900AA transmitter, $1,850; stereo adapter, $295; stereo receiver, $2,000; and IFB100 transmitter, $1,395. (All items may be purchased individually.)

Zaxcom Inc. | 973-835-5000 | The Zaxcom Wireless ENG package is composed of four units: a TRX900AA transmitter, an STA100 stereo adapter, an RX900S stereo receiver, and an IFB100 transmitter for IFB communication. These items can also be purchased separately in case all of the package components are not needed.

The cornerstone of the system is the TRX900AA transmitter. Although it's smaller than most lav and microphone transmitters, the TRX900AA can do much more. It not only functions as a superb wireless transmitter, but can also record up to 12 hours of digital audio on a 2 GB SanDisk or Transcend miniSD memory card. The TRX900AA runs for up to eight hours on two AA lithium ion batteries, weighs only four ounces and easily fits into a front shirt pocket. It employs digital modulation for noiseless transmission. For complex shoots with multiple cameras, up to 50 transmitters in the same frequency block can be used simultaneously. An LCD menu is provided to control all essential functions.

The Zaxcom system allows you to select from frequencies within a block of 30 channels between 518 and 870 MHz, virtually guaranteeing that you will find a channel free of interference from other sources.

The TRX900AA also has modular add-on capability to provide additional functions. A small unit, about the size of a poker die, can be mounted on the side to add IFB communication. The unit also generates timecode and can receive timecode when used in conjunction with the internal IFB receiver and the optional IFB100 transmitter. The audio frequency response is 20 Hz to 16 kHz.

The STA stereo adapter is a very compact interface that can be mounted on the side of the TRX900AA for stereo transmission from a line level source. It includes an adapter that enables you to connect two XLR audio inputs. This device also includes timecode input and output. Audio recorded onto the TRX900AA internal memory card maintains the same timecode as the audio being sent to the camera.

The RX900S stereo receiver is equally compact and powered by either four AA batteries (providing four hours of running time), or a 12 V power supply. It includes an adapter with two XLR outputs for true two-track separation, or it can send a single mono signal to two separate channels if desired. The RX900S utilizes high quality 24-bit D/A conversion with maximum distortion of 0.01 percent and a system dynamic range of 105 dB.

Finally, the package includes the IFB100 transmitter. It transmits IFB audio, timecode and remote control signals to the transmitter. ("Transceiver" is a more accurate label, as the TRX900AA can both receive IFB communication as well as transmit audio.)

Aside from providing IFB talkback capability to TRX900 units in the field, the IFB100 also enables multi-track recording by sending out a single timecode that multiple transceivers can lock onto. The separately recorded audio tracks can then be brought into sync during post production.

The IFB100 includes an adapter that allows the connection of two line-level XLR sources. It also includes input jacks for timecode. The timecode reader/generator runs at all common frame rates and directly accepts SMPTE timecode from an external source.


Most of my work involves documentary production, and wireless microphones are indispensable. The Zaxcom wireless ENG package has capabilities that create possibilities far beyond what a typical wireless system can offer.

As mentioned, the central transmitting device is the TRX900AA. It can run on two standard AAs, although you'll get more operating time with lithium ion cells. The TRX900AA includes an LCD screen that lets you navigate through an impressive array of features and adjust their settings. There are two menu levels. The basic one allows you to adjust gain, frequency, timecode frame rate, and IFB earpiece setting (if using the IFB feature). If you hold down the menu button when turning on the power, you get an extended menu. This includes a high pass filter, limiter, mono/stereo selection and additional IFB controls.

A wireless system needs to be easy to set up and configure. You don't want to run into some kind of frequency mismatch between transmitter and receiver when you need to be shooting. Zaxcom scores well in this category. As soon as you power up the transmitter, the operating frequency appears on the LCD screen. Similarly, when you power up the receiver, just press the menu button once to display the frequency. It's also very easy to change frequencies if necessary. The RX900S provides an efficient scanning function. When you execute a scan, it automatically selects the quietest channel. You can then quickly match the transmitter to that frequency.

But how about the sound quality? That is the fundamental purpose of the system, so I set out to test it. I attached the RX900S receiver to a Panasonic DVX200 DVCPRO HD camera. The RX900S is equally well designed and simple to operate. It runs on AA batteries or AC, and also includes a small LCD screen for menu controls.

Getting the system up and running was quick and painless. After powering both transmitter and receiver, I received the input from an attached microphone.

At this point, I monitored the microphone signal through a pair of headphones connected to the camera, and I have to say that the clarity of the sound was astounding. The channel was, to my ears, completely noise free. I could only hear the sound from the microphone against a background of crystal silence. I have never heard a wireless transmission this clean before.

In my tests, I found that the Zaxcom system performed exceedingly well and is extremely versatile. But I do see an opportunity for some small improvements. The receiver lacks any means for attaching it to a camera or anything else if desired. (However another company, the BEC Group, makes a mounting device to address this problem.)

The Zaxcom system offers unparalleled versatility by offering the STA100 stereo adapter, which allows you to connect two inputs to the transceiver. However it is limited to a line level input, which doesn't allow you to connect and transmit with two microphones unless they are routed through a mixer or pre-amp first. I found this disappointing because it places limitations on what is otherwise a revolutionary design. Similarly, the IFB transmitter also takes a line level signal. If mic levels could be accommodated it would certainly make the system more versatile.


The Zaxcom ENG wireless system is a remarkable achievement in audio engineering that deserves much more attention. Innovations such as two-track stereo on a single transmitter, memory card recording and IFB communication give this system enormous capability. But at the center of it all is an astounding clarity of sound quality. The signal-to-noise ratio is awesome. This is a system that offers unparalleled versatility and sound clarity that to my knowledge is unrivalled.

Geoff Poister, Ph.D., is a member of the Film and Television faculty at Boston University and a regular contributor to TV Technology.