Model 545DR User Guide Issue 1, May 2022
Studio Technologies, Inc. Page 7
Model 545DR
INTERCOM INTERFACE
number of devices such as beltpacks. With up to
240 milliamperes (mA) of current available, a typical
broadcast application which uses up to three BP-325
beltpacks can be supported. In many applications,
this can eliminate the need for an external intercom
power supply, reducing total system cost, weight, and
required mounting space. The power supply output is
monitored for over-current and short-circuit conditions.
Under rmware (embedded software) control the out-
put will automatically cycle o 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 545DR
using the Dante audio-over-Ethernet media network-
ing technology. Audio signals with a sample rate of
48 kHz and a bit depth of up to 24 are supported.
Audio transmitter (output) and receiver (input) chan-
nels on associated Dante-enabled devices can be
assigned to the Model 545DR using the Dante Con-
troller application. This makes it simple to select
the way in which a Model 545DR ts into a specic
application.
Analog Hybrids with Auto Nulling
Circuits referred to as “hybrids” interface the Dante
transmitter (output) and receiver (input) channels with
the two channels of the party-line circuit. 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 545DR’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 545DR’s sophisticated hybrid auto nulling
function uses a combination of digital and analog
circuitry under microprocessor control to achieve
signicant trans-hybrid loss. This return-loss “null”
is achieved by making a series of rmware-directed
adjustments to account for the resistive, inductive,
and capacitive conditions that are present on the
connected party-line cabling and user devices.
Whenever the Model 545DR’s auto null button is
pressed, or the STcontroller application is used, digital
circuitry adjusts the hybrids to achieve their 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 545DR’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-
room. Using active lters 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 substan-
tial “nulls.” Moreover, the Model 545DR’s party-line
intercom power source oers a unique level of perfor-
mance; its ability to deliver power while maintaining
audio quality is simply unmatched.
Audio Meters
The Model 545DR 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
conrm correct operation. During normal operation
the meters oer rapid conrmation of audio signals
owing in to and out of the Model 545DR unit.
Status Display
LED indicators are provided on the Model 545DR’s
front panel, oering a status indication of the party-line
(PL) power source, party-line (PL) activity status, and
the two auto null functions. Two other LEDs oer a
direct indication of what power source or sources
are connected to the Model 545DR. The STcontroller
application provides a real-time “virtual” status display
of the unit’s PL power source, PL activity, and auto
null functions.
Call Light Support
RTS TW-compatible party-line intercom user devices,
such as the BP-325 beltpack, provide a call light func-
tion using a 20 kHz square-wave signal that is added
to the designated audio path. To achieve optimal
audio performance this signal, along with essentially
all content above 10 kHz, is normally removed from
the audio signal that is sent out the Model 545DR’s
Dante transmitter (output) channels. It’s also removed
