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DACS App Note

Using the Intercom Switch Product with DACS (#23)

ASTi has developed a version of the DACS that specifically addresses the requirement for a simple multi-net intercom capability between multiple operators.

The new product is essentially a large intercom switching network that retains the same developmental flexibility in terms of hardware and software as other ASTi Model Builder products. This permits the operator to reconfigure the intercom layout for different types of training platforms or exercises. This custom configuration is referred to as "the custom model" and is discussed in more detail below.

Audio Distribution (between Headset/mic and DACS digital switch)

Audio information will be distributed in either an analog or digital format. The choice of analog or digital is dependent on the training environment and the needs of the customer. The analog solution is less expensive and is best used in low noise environments where the operator stations are in close proximity to each other. It is important to remember that all switching is conducted in the digital domain and that the terms analog or digital here refer only to the mechanism employed to transmit the audio signals to and from the central digital switch.

The digital distribution mechanism is based upon a proprietary TDM architecture that includes local conversion of the voice signals and some unique benefits in terms of interfacing to operator control panels as discussed below. The net result of this digital distribution is a very clean and simple wiring installation (i.e. a single Cat5 cable loop to distribute all voice and panel data.)

Operator Controls

For the Analog distribution system discrete control variables for the operator stations are passed to DACS through a Host Computer via an ethernet link. This implies that there must be a host computer, and that it must be able to sense the operator control actions (usually either on a "softpanel", a replica of a panel on a workstation monitor, or from electrical switches on a mechanical panel via general purpose I/O interface equipment).

These signal distribution and sensing problems are elegantly resolved using the RIU/TDM digital distribution technology. The voice and switch signals are encoded at the panel and operator position and transmitted back to the central DACS node over a single Cat5 cable loop. (More information regarding the features of this architecture are available in the RIU App Note #009 and the Communication Operator Panel Product Flyer). This digital solution is also very robust for use in high noise environments or where the operator stations are some distance apart. (Cable loop distances of 500 feet are permitted.)

Signal Conditioning and Cabling

Cabling is not an issue for the digital TDM/RIU architecture. For the analog distribution ASTi will provide the information necessary for you to build your own interface equipment or you can purchase audio cables and headsets from our catalog. If signal conditioning or impedance matching is required custom interface equipment will be needed.

The Audio Interface Units (AIU) is a proprietary amplifier module (approximately the size of a paperback novel) that ASTi has designed to provide signal conditioning and impedance matching for the majority of applications (including small PA speakers or military headsets using phantom power - please refer to the AIU brochure for more information).

Product Configurations

The analog distribution platform comes in 3 base configurations for a single DACS node ; 8, 16 and 24 operators corresponding to whether one, two, or three Waveform Synthesizer cards are fitted.

For the RIU/TDM distribution, since it is possible to install up to twenty four operators on a single tdm loop, and it is possible to install up to three TDM DSP cards in a node, the maximum number of operators is seventy two before it is necessary to revert to a multi-node solution. Pricing information for the different versions of the system is included on the relevant product information sheets.

Where larger configurations of operators are required, multiple nodes can be networked together. This work can be accomplished by the customer using standard DIS modules available from ASTi or can be contracted for by ASTi as a turnkey solution. However, these larger networks will frequently require other communications features such as point-to-point connection logic which exceed the purview of the simple intercom net product and require use of the DACS network product range.

Operator Controls

Whatever comm net resources are allocated to each operator, the attributes of these nets may be changed on the fly by the operator using his control panels. Alternatively, in the absence of an operator radio contol panel these parameters may be set from the (customer supplied) keyboard & monitor controls using Model Builder. These include all the standard intercom functions such as:

  • PTT or Hotmic
  • Channel number for each net
  • Individual and overall volume
  • Transmit/ Monitor status for each net (all nets may be monitored simultaneously)

Custom System Configuration - The "Custom Model"

In addition to the above operator controls the system administrator is provided with an interactive command-line interface that allows on-line changes to the system configuration. This allows system resources to be allocated. This concept of a "custom model" is confusing to many of our first time customers. Since they have been led to understand that ASTi has an off-the-shelf solution for their application, "What's to customize?"

In a conventional hard-wired intercom system, certain decisions would be made during the ordering and installation process. For instance, at the most basic level, one would decide how many operator stations to connect to the system and how many channels or separate nets to give each operator. On a hard wired system this would then be a permanent feature of the installation. With an ASTi system these features can be changed at will. For instance one operator may be allocated sixteen nets and another four, or a subgroup may be allocated private nets that cannot be accessed by other participants. Levels of override priority may also be established.

The system administrator may also set exercise parameters such that two subgroups are completely independent, or, the number of simultaneous voicestreams that are allowed on a single net. In another installation it may be required to connect in a telephone input or a live radio source. And so on.... We find that the customer's "standard requirement" usually turns out to have several unique aspects as soon as pandora's box is opened and he understands that he is not being forced into a one-size-fits-all solution. It frequently transpires that in addition to the "standard intercom" requirement he had several other features that he was planning to engineer as bolt-ons to the basic system (at significant risk and cost). It is this ability to easily reconfigure these system parameters and add additional functions that makes this intercom so useful and expandable.


A training course for using the system software is offered and is highly recommended for first time users and especially recommended if you decide to develop your own intercom model (configure the system resources for each operator) For more advanced applications, ASTi can develop your intercom model. The cost of this service is driven by the complexity of the model and is typically between $1,000 and $10,000.

Growth and Expansion

The DACS is the basic building block for systems of considerable size and functional complexity. It is extremely unlikely that your communication system requirements will exceed the upper limits of the DACS' capability.