Lectrosonics UDR195 - Manual (Page 6)

GENERAL TECHNICAL DESCRIPTION
The DR195 consists of two high performance, dual-conversion
receivers operating simultaneously. The audio outputs of the
receivers are blended in a ratio controlled by the compared
signal to noise ratios of the receivers. The RF section is
mounted on a separate circuit board, permitting frequency
changes by simply interchanging the RF section assembly.
The RF performance is extremely stable over a very wide
temperature range, making the DR195 perfectly suited to
mounting in studio equipment racks. The proprietary audio
processing includes a dual-band compandor and dynamic
noise filter for very low distortion and a superior signal to
noise ratio. The squelch system is operated by a separate pilot
tone and mutes the audio output directly at the output connec­
tor. The audio output is calibrated for exact level matching,
with both peak LED and average VU indicators.
MODULAR UHF/VHF RF SECTION
A unique modular design is employed to simplify frequency
changes. By simply interchanging the RF section module, the
frequency can easily be changed without test equipment or
soldering. All RF stages are contained in the removable RF
section. The output of the RF section is audio, so changes to a
new frequency, even from UHF to VHF, are simply a matter of
changing out the RF module. This modular design provides
the RF reliability of a fixed frequency design and the fre­
quency flexibility of a switchable design.
As a side note, it is important to realize that frequency changes
“on the fly” cannot be made on any type of wireless system.
This is especially true in multi-channel applications where
changing the frequency of one system could produce all kinds
of new intermodulation problems with other systems operating
in the same location. In reality, frequency changes can only be
made on any wireless system during idle periods when the
systems are not in use. For example, if there is a problem with
a transmitter being used on stage that requires a frequency
change, the change cannot be made without interrupting the
program or waiting until there is time between shows.
SIX-POLE HELICAL RESONATOR FRONT-END
The DR195 utilizes dual six-pole helical resonator front-end
filtering, 3 pairs for each receiver. The helical resonators are
much larger than those typically used for wireless microphone
frequencies, producing an extremely high filtering “Q.” The
result is that the DR195 is not affected by high power signals
close to the carrier, and offers extremely high image rejection.
GaAs FET FRONT-END FILTER COUPLING
The DR195 utilizes ultra low noise GaAs FET amplifiers in
the front-end section to compensate for the required losses
between filter stages. The GaAs FET devices are extremely
quiet, especially at the higher frequencies in the UHF band.
DOUBLE BALANCED DIODE MIXERS
A double balanced diode mixer is used in the DR195 to
produce the 10.7 MHz IF signal. The mixer produces output
at only the sum and difference signals, with minimal spurious
signals. This mixer offers a very high overload threshold and
a high degree of isolation between ports.
8 POLE LINEAR PHASE FILTER
The 1st IF amplifier is a 4 stage amp with 2 poles of filtering
after each stage. The filters are high quality, low distortion,
constant group delay ceramic filters. This special type of filter
is needed to accommodate the wide deviation of the 195
system.
RF MODULE
HELICAL
RESONATOR
GaAS
FET
HELICAL
RESONATOR
GaAS
FET
HELICAL
RESONATOR
HELICAL
RESONATOR
GaAS
FET
HELICAL
RESONATOR
GaAS
FET
HELICAL
RESONATOR
174-608
mHz
174-608
mHz
XTAL
CONTROLLED
1ST
OSCILLATOR
8 POLE
LINEAR PHASE
FILTER
455KHZ
BP
FILTER
RF LEVEL
LEDs
IF
AMP
2ND MIXER
&
IF AMP
COUNTING
DETECTOR
50 KHZ
LP FILTER
HI-LEVEL
DIODE MIXER
XTAL
CONTROLLED
2ND
OSCILLATOR
HI-LEVEL
DIODE MIXER
IF
AMP
2ND MIXER
&
IF AMP
COUNTING
DETECTOR
50 KHZ
LP FILTER
RATIO
COMBINER
&
OPTI-BLEND
8 POLE
LINEAR PHASE
FILTER
455KHZ
BP
FILTER
RF LEVEL
LEDs
2:1
EXPANDER
TREBLE
2:1
EXPANDER
BASS
23 KHZ
LP
FILTER
VARIABLE
CUT-OFF
LP FILTER
AUDIO
AMPLIFIER
HEADROOM
ADJUST
HEADPHONE
OUT
OUTPUT
LEVEL
ADJUST
XLR
OUT
PILOT
TONE
MUTE
Figure 1 - DR195 Block Diagram
6