VR Field Receiver
LECTROSONICS, INC.
The result is that the same signal entering the rear
panel Antenna Inputs is presented to each receiver
module and to the pass-through rear panel Antenna
Output jacks. The design allows each receiver module
to be used independently.
Microprocessor Control
System setup parameters and control signals from DSP
are used by an 8-bit microprocessor to both set up and
control the VR Field System in general and to control
each individual receiver module (or receiver module
pair if they are used in ratio or frequency diversity
mode).
Initial system setup and control can be accomplished
through front panel controls, or via software using
convenient USB or RS-232 I/O ports. The setup pa-
rameters plus control signals from the DSP are used to
control the installed receiver modules, audio processing
and audio output.
The microprocessor also receives RF signal strength
information from each receiver module and information
from the DSP concerning transmitter operation. This
information is used both to control the VR Field System
and to display current status in various LCD menus or
setup screens. (See VR Field System Controls and
Functions, and Menus and Setup Screens.)
Frequency Tuning Groups
The VR Field System provides four factory preset in-
termodulation free frequency groups (A through D) and
two user programmable frequency groups (U and V).
The factory groups have been selected to avoid inter-
modulation problems. Each factory group contains
eight frequencies.
The user programmable frequency groups can have up
to 16 frequencies per group, per frequency block.
Digital Signal Processor
The analog detector output from each receiver module
is digitized and sent to a DSP. The DSP processes
the digitized detector output according to the active
settings. These signals include Compatibility Modes,
Diversity Modes and SmartNR
™
modes.
The DSP also detects the Pilot Tone used to control
the receiver module’s squelch (only in 400 Series, 200
Series and IFB Compatibility Modes – see DSP-Based
Pilot Tone).
In addition to the audio, a 1 kHz tone is also available
from the DSP. This tone is used to preset the VR Field
System’s audio output levels according to the input re-
quirements of any attached equipment and for diagnos-
tic purposes. (See Level Setup Screen.)
Each of the six audio channels is then sent through its own
D-A converter to recover the original analog audio. The
analog audio is then sent to both the appropriate Audio
Output Amplifier and to the Headphone Mixer and Amp.
Note: While all audio channels are sent to the
respective Audio Output XLR jacks, only one audio
channel at a time may be monitored via the front
panel PHONES jack. (See Headphone Mixer and
Amp.)
Compatibility Modes
The VR Field System was designed to be compatible
with Lectrosonics Digital Hybrid (400 Series) transmit-
ters and will yield the best performance when operating
in Digital Hybrid mode. However, due to the flexibility
of digital signal processing, the VR Field System is
also able to operate with Lectrosonics 200 Series, 100
Series and IFB transmitters, and certain non-Lectroson-
ics transmitters in special compatibility modes. (Contact
the Lectrosonics Sales Department for a complete list
of compatible transmitters.)
Ratio Diversity and Frequency Diversity Reception
Both ratio diversity (OptiBlend
™
) and Frequency Diver-
sity combine the outputs of two adjacent receivers.
OptiBlend
™
is a ratio diversity method which combines
the audio output from two adjacent receiver modules
(1-2, 3-4 or 5-6) relative to the RF signal input levels at
both receivers.
Frequency Diversity pairs two transmitters with two
adjacent receiver modules. (The receiver pair combina-
tions are the same as those used for OptiBlend: 1-2,
3-4 or 5-6.) Each transmitter/receiver combination in
the pair is tuned to a different frequency. The RF signal
level at each receiver is monitored and the audio is
blended in a manner similar to ratio diversity.
In both cases, because of the mixing function, the
blended audio is duplicated at each XLR jack associ-
ated with the receiver pair. (See also Switched Diversity
Reception.)
DSP-Based Pilot Tone
The 400 Series, 200 Series and IFB systems use a
DSP generated ultrasonic pilot tone from the transmitter
to control the receiver audio muting (squelch). The DSP
monitors all incoming audio and generates a Pilot Tone
Detect signal if a pilot tone is detected. The Pilot Tone
Detect signal is routed to the microprocessor to enable
or disable squelch depending on the PilotBP setting
for that receiver module. (See PilotBP Setup Screen.)
Squelching is performed in the DSP.
In 400 Series mode, the pilot tone frequency is differ-
ent for each of the 256 frequencies in the tuning range
of a system (frequency block). This eliminates squelch
problems in multichannel systems such as the VR Field
System which use a common antenna and where a
pilot tone signal can appear in the wrong receiver via
intermodulation products. Using the DSP to detect the
pilot tone also eliminates the need for fragile crystals.
In 200 Series and IFB modes, only one pilot tone fre-
quency is used on all channels, emulating the original
crystal-based system. In other compatibility modes (100
Series and Mode 3), no pilot tone is used.
