Studio Technologies 47A - Manual (Page 7)

Model 47A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 7
Remote sports broadcast applications are
especially sensitive to this requirement.
The Model 47A’s sophisticated auto null-
ing function uses analog circuitry under
microprocessor control to achieve sig-
nificant trans-hybrid loss. This return-loss
“null” is achieved by making a series of
adjustments to account for the resistive,
inductive, and capacitive conditions that
are present on the connected 2-wire party-
line circuit. A party-line’s condition is the
sum of the impact made by the type and
quantity of cable, the connected user de-
vices, and the intercom power source.
Whenever a user presses one of the
Model 47A’s auto null buttons digital
circuitry adjusts the analog hybrids to
rapidly achieve their maximum return-loss.
The nulling process takes less than ten
seconds for each channel of an interface.
However, it’s important to note that while
the nulling process is automatic, it only
takes place upon user request. This can
lead to more stable and consistent audio
performance when a hybrid is exposed to
the varying 2-wire conditions often found
in broadcast applications. The param-
eters obtained during the nulling process
are stored in non-volatile memory; mains
power interruptions won’t require the auto
nulling function to again be performed.
A sine-wave audio tone is generated for
use during the auto nulling process. The
frequency is software-controlled to maxi-
mize the ability of the hybrid circuits to
reach a “deep” null. In addition, at the
beginning of each auto null sequence a
short period of 24 kHz tone is sent to the
associated 2-wire party-line interface. This
serves as a microphone disable (“mic kill”)
signal for user devices such as the RTS
BP325. By automatically disabling “open”
microphones the auto nulling process can
achieve better performance.
4-Wire Interfaces
Associated with the 4-wire portion of the
Model 47A’s interfaces are analog line-
level inputs and outputs. These are in-
tended to interconnect with a variety of
4-wire devices, including matrix intercom
systems, audio-over-fiber transmission
systems, and other specialized audio
equipment. The input and output circuitry
is transformer-coupled to minimize the
chance of hum, noise, or ground “loop”
issues. A key characteristic of the Model
47A’s design is the ability to select the
4-wire input and output nominal levels.
This helps to ensure compatibility with
virtually all audio equipment. Front-panel-
accessible DIP switches allow the nominal
levels to be configured from among four
choices: 0, +4, +6, or +8 dBu. The 0 dBu
setting was specifically provided for com-
patibility with Clear-Com matrix intercom
systems. The +4 dBu setting allows
“standard” audio signals to be directly
connected. Digital matrix intercom sys-
tems from Riedel® can be effectively
connected using the +6 dBu setting. And
the +8 dBu setting allows proper level
matching with the popular ADAM®-Series
of matrix intercom systems from RTS.
This setting also applies to the related
RVON-I/O VoIP product.
The Model 47A contains eight 5-segment
LED level meters. Four of the meters are
provided for each interface, with two
displaying the level of the signal being
received from the 4-wire source and
two displaying the level being sent to
the 4-wire output. During installation and