In the entertainment sector, wireless microphone systems are often used for the transmission of voice and music because wireless microphones look better than cabled models while also offering many practical advantages for artists and technicians. The implementation calls for superior PCBs and connectors.

Major music events, concerts, musicals or theatre performances without wireless microphones are inconceivable today. Dance, movement, stage show - all this would be impossible without wireless technology. Wireless microphones allow the "Starlight Express" to roll and the guitarist to rock across the stage. Wireless microphones are also frequently deployed in the film sector, in the television studio and at sporting events. As almost invisible clip-on microphones, they capture the words of the principal actors, and are found in the broadcaster's colours on the sidelines during interviews - no cable bearer is needed.

For an event's technicians, wireless microphones and wireless monitoring (the clip-on earphone for artists) also simplify the work significantly. There are fewer cables to install and tape, and when it comes to renting a venue, time is money. The heavy and not particularly space-saving monitor speakers can be replaced by wireless monitoring, which is easier on the ears. The reporter can quickly be given a microphone for the coverage.

The Digital 9000 wireless system from Sennheiser is used in professional events due to its high audio quality level. Wireless microphones usually use the UHF frequency range because it offers good propagation conditions for the microphone signal and enables systems with many channels and a high audio quality level. Several hundred thousand radio microphones are in use in Germany alone, and the trend towards more wireless technology continues. The number of wireless segments needed is also growing steadily in large productions. For example, the last Eurovision Song Contest in Baku called for more than 100 wireless microphone segments.

Connected without Wires

Sennheiser, one of the world's leading manufacturers of microphones, headphones and wireless transmission systems, developed the Digital 9000 system for these demanding application environments.

The digital, wireless high-end system is targeted at professional radio, theatre, musicals and large live events. It features a high audio quality level and operational reliability; its extraordinary frequency efficiency allows the user to achieve the highest channel counts, even in a dense frequency environment. Special highlight: The system can transmit completely without the audio compression normally encountered in the digital area - whereby the original sound is fully retained.

The core of the Digital 9000 wireless system is the modular EM 9046 receiver, which, with a bandwidth of 328 MHz, covers the UHF frequency range from 470 to 798 MHz. The multichannel receiver accommodates up to eight receiver channels. The receiver's job is to convert the transmitter's radio signals back into electrical signals and forward them, for example, to a mixing desk. It is also possible to monitor and control the entire microphone system at the receiver.

Hybrid Midplane as the Basis

The receiver's central element is a highly complex PCB solution that was developed, tested and verified by Harting Integrated Systems (HIS). This is a customized hybrid midplane, which means that in addition to the digital data bus, a high frequency, wire-bound transmission on the PCB was also implemented. In order to fulfil these tough requirements, an 8-way multi-layer midplane was developed in a strip-line design with a PCB thickness of 3.2 mm. In order to achieve optimal EMC shielding, the outer layers here do not conduct signals and instead are used as ground potential. The PCB has a surface area of roughly 440 cm2 and is made of a flame-retarding epoxy resin with fiberglass cloth (FR4) that is suitable for applications in the GHz frequency range.

The midplane, which was developed by Harting Integrated Solutions and which has components mounted on both sides, is the core of the Digital 9000.

The positioning of the necessary connectors and the placement of the conductor paths on the board are implemented on the basis of the net or pinning list. Cadence Allegro design software is the professional tool used to disentangle and design the data buses, and also to simulate all electrical parameters. The HF bus midplane with connectors and the influence of the daughter cards on these was developed and optimized with Agilent/ADS simulation software.

Two-sided Mounting

In a midplane, components are mounted on both sides of the PCB. For the daughter cards, front-sided plug-in positions were implemented, while a back-side connection was created for the rear transmission modules. In order to achieve bi-directional transmission of the digital data bus signals from the PCB to the daughter cards and rear-transmission modules, the Harting har-bus HM standard backplane connector with a 2-mm pitch was used. The har-bus-HM Power solutions provide the power supply to the modules.

HM connection systems form the basis for setting up high performance backplanes and midplanes for control and industrial computer systems in 19-inch technology or for customer-specific solutions. The board-to-board connectors are available in press-in technology for backplanes/midplanes and in soldered versions for the daughter cards.

Mini Coax connectors from Harting are used for processing the 2-GHz signals on the midplane/PCB. These allow multipolar, coaxial and high frequency data transmission for board-to-board and cable-to-board applications. Straight and bent contact inserts in press-in technology and SMT/SMC are available for device integration. The housings allow applications up to IP 65.

Power Connection

The midplane's power connection was implemented with a D-Sub-Mixed connector, which helps to transmit both voltage and control signals to the PCB. This connector family from Harting combines the advantages of a standardized industrial interface connector with the flexibility of a customer-specific product. The D-Sub Mixed connector design is based on customary D-Sub housing sizes. In addition to standard contacts, one connector can also include diverse contact types, such as high current, high voltage, coaxial or pneumatic, depending on the customer requirements. The design guarantees complete shielding and helps prevent electromagnetic interference.

Before the midplane was implemented in the multichannel receiver, simulations and special measurements at Harting verified that the application solution functioned flawlessly.

For example, measurements of the isolation between the transmission channels were made in various frequency ranges, crosstalk measurements were made to verify that the crosstalk levels were in the required attenuation range in dB, and impedance measurements were made in the various layers in order to demonstrate the AC resistance.

Extensive simulations that were carried out during and after the development phase in Harting's own "Signal Integrity" department substantiated the flawless signal transmission on the midplane. All the measurement and simulation results fulfilled Sennheiser's demanding specifications.

Complete Service

As a Harting Technology Group member, Harting Integrated Solutions (HIS) offers complete service for customer-specific backplanes, midplanes and PCB-based systems, from the design through to the finished product. From the circuit development to the design simulations to rapid prototyping, backplane projects are implemented swiftly and the finished product is delivered reliably and on time. Before shipment, all products undergo extensive mechanical and electronic performance tests in accordance with recognized industry standards and customer specifications. In the framework of the HIS quality assurance program, progressive signal analysis functions guarantee the outstanding performance of the high-speed backplanes. The well-engineered design allows reliable operation for many years, even in demanding application environments. Thanks to the successful cooperation between Sennheiser and Harting the Digital 9000 system guarantees outstanding reception, whether on stage or in TV studios.