Datasheet

Studio Technologies, Inc. Model 45DC Intercom Interface, Issue 3, Page 2
party-line intercom circuit rather than two single-
channel circuits. These 2-channel circuits, typically
supported by equipment from RTS, are commonly
used in broadcast applications.
Party-Line Interfaces
The Model 45DC’s two party-line intercom interfaces are optimized
for connection with two single-channel party-line circuits and user
devices such as those associated with equipment from Clear-Com.
(While the Model 45DC will function in a limited manner with a
2-channel RTS TW circuit, the Model 45DR Intercom Interface is
the much-preferred choice.) Each interface has a party-line ac
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tive detection function to ensure that should a beltpack or active
party-line circuit not be connected the Model 45DC’s interface
circuitry will remain stable. This unique feature makes certain that
objectionable audio signals, including oscillations and “squeals,”
won’t be sent to other Dante-enabled devices.
A significant capability of the Model 45DC’s two party-line inter
-
com interfaces is their ability to supply DC power and 200 ohm
AC terminations to “create” two independent intercom circuits.
The 28 Vdc output can power user devices such as beltpacks.
With up to 150 milliamperes (mA) of current available, a typical
entertainment application could connect up to three RS-501 or five
RS-701 beltpacks to each of the Model 45DC’s two interfaces.
In many applications this can eliminate the need for an external
intercom power supply, thereby reducing total system cost,
weight, and required mounting space. The power supply outputs
are monitored for over-current and short-circuit conditions. Under
firmware (embedded software) control the outputs will automati
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cally cycle off and on to help prevent damage to the circuitry and
connected equipment.
Dante Audio-over-Ethernet
Audio data is sent to and from the Model 45DC using the Dante
Audio-over-Ethernet media networking technology. Audio signals
with a sample rate of 48 kHz and a bit depth of up to 24 are sup
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ported. Audio input (receiver) and output (transmitter) channels
on associated Dante-enabled devices can be assigned to the
Model 45DC using the Dante Controller software application.
This makes selecting the way in which a Model 45DC fits into a
specific application a simple matter.
Analog Hybrids with Auto Nulling
Two circuits referred to as “hybrids” interface the Dante input
and output channels with the two party-line interface channels.
The hybrids provide low noise and distortion, good frequency
response, and high return-loss (“nulling”), even when presented
with a wide range of party-line conditions. Unlike telephone-line
(“POTS”) oriented DSP-based hybrid circuits, the Model 45DC’s
analog circuitry maintains extended frequency response. With a
passband of 100 Hz on the low end and 8 kHz on the high end,
natural-sounding voice signals can be sent to and received from
a party-line circuit.
The Model 45DC’s sophisticated hybrid auto nulling function uses
a combination of digital and analog circuitry under microprocessor
control to achieve significant trans-hybrid loss. This return-loss
“null” is achieved by making a series of firmware-directed adjust
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ments to account for the resistive, inductive, and capacitive condi
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tions that are present on the connected party-line cabling and user
devices. Whenever one of the Model 45DC’s auto null buttons is
pressed digital circuitry adjusts the associated hybrid to achieve
its maximum return-loss in less than 15 seconds. While the nulling
process is automatic, it only takes place upon user request. The
resulting null parameters are stored in non-volatile memory.
Pro Audio Quality
The Model 45DC’s audio circuitry was designed in the spirit of
professional audio equipment rather than that found in typical
party-line intercom gear. High-performance components are used
throughout, providing low-distortion, low-noise, and high head
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room. Using passive and active filters the frequency response of
the audio channels is limited to nominally 100 Hz to 8 kHz. This
range was selected to provide excellent performance for human
speech while maximizing the ability of the hybrid circuits to create
substantial “nulls.”
Audio Meters
The Model 45DC contains two sets of 5-segment LED level meters.
Each set of two meters displays the level of the signals being sent
to and received from a party-line interface channel. At the time
of installation and setup the meters are invaluable in helping to
confirm correct operation. During normal operation the meters
offer rapid confirmation of audio signals flowing in to and out of
the unit. Additional LED indicators are also provided on the front
panel, offering a status indication of the party-line DC power
sources, party-line activity status, and the auto null functions. Two
other LEDs offer a direct indication of which source is powering
the Model 45DC.
Call Light Support
Typical single-channel party-line intercom circuits provide a call
light function by way of a DC voltage applied to the audio path.
The Model 45DC can detect call light activity, convert it to a
20 kHz audio tone, and transport the tone over the Dante audio
path. A Model 45DC unit at the “far end” will detect the tone and
re-generate the call signal as a DC voltage on the audio path.