Lectrosonics UT195 User Manual
UR195
COMPACT UHF RECEIVER
OPERATING INSTRUCTIONS
and troubleshooting guide
LECTROSONICS, INC.
Rio Rancho, NM
Rio Rancho, NM – USA
1
Table of Contents
INTRODUCTION TO THE 195 SYSTEM .............................................................. 3
UT195 TRANSMITTER .......................................................................................................... 3
UM195 TRANSMITTER ......................................................................................................... 3
DUAL-BAND COMPANDOR ................................................................................................. 3
75kHz DEVIATION.................................................................................................................3
NO PRE-EMPHASIS/DE-EMPHASIS ................................................................................... 3
EXCEPTIONAL THERMAL STABILITY ................................................................................ 3
GENERAL TECHNICAL DESCRIPTION - UR195 RECEIVER........................... 4
SIX-POLE HELICAL RESONATOR FRONT-END ............................................................... 4
GaAs FET FRONT-END FILTER COUPLING ..................................................................... 4
DOUBLE BALANCED DIODE MIXERS ................................................................................ 4
10 POLE LINEAR PHASE FILTER ....................................................................................... 4
DIGITAL PULSE COUNTING DETECTOR .......................................................................... 4
2:1 EXPANDER (Dual–Band Compandor) ........................................................................... 5
PILOT TONE MUTE (SQUELCH) ......................................................................................... 5
FRONT PANEL CONTROLS AND FUNCTIONS ................................................. 5
PWR LED ............................................................................................................................... 5
PILOT LED ............................................................................................................................. 5
TRANSMITTER AUDIO LEVEL METER .............................................................................. 5
RF LEVEL INDICATORS ....................................................................................................... 5
OUTPUT LEVEL ADJUST AND RANGE SWITCH .............................................................. 5
POWER SUPPLY .................................................................................................................. 5
MONITOR ............................................................................................................................... 5
POWER SWITCH .................................................................................................................. 5
AUDIO OUTPUT ..................................................................................................... 5
REAR PANEL CONTROLS AND FUNCTIONS ................................................... 6
EXTERNAL POWER JACK ................................................................................................... 6
AUDIO OUTPUT XLR JACK ................................................................................................. 6
RANGE SWITCH ................................................................................................................... 6
ANTENNA CONNECTOR ..................................................................................................... 6
ANTENNA USE AND PLACEMENT ..................................................................... 7
OPERATING INSTRUCTIONS .............................................................................. 8
UR195 REPLACEMENT PARTS and ACCESSORIES ....................................... 8
TROUBLESHOOTING ............................................................................................ 9
POWER SUPPLY AND FUSE ............................................................................................... 9
PILOT TONE SQUELCH ....................................................................................................... 9
ANTENNAS AND RF SIGNAL STRENGTH ......................................................................... 9
AUDIO SIGNAL QUALITY ..................................................................................................... 9
SERVICE AND REPAIR ....................................................................................... 10
RETURNING UNITS FOR REPAIR ..................................................................... 10
SPECIFICATIONS AND FEATURES .................................................................. 11
LIMITED ONE YEAR WARRANTY ..................................................... Back cover
2
INTRODUCTION TO THE 195 SYSTEM
The 195 Series system was designed for the most critical studio and
sound reinforcement applications. The system design represents a
significant step forward in wireless microphone technology. Every
stage in the entire audio/radio chain from transmitter input to
receiver output was evaluated and analyzed to produce the operating
parameters and performance requirements for this entirely new
design. The audio system provides the lowest distortion and best
signal to noise ratio of any wireless mic system ever built. The RF
link is extremely stable, providing the highest reliability and
freedom from drop outs and interference.
The UR195 employs the most advanced circuit and mechanical
design ever applied to a wireless microphone receiver. The audio
processing is the finest quality system ever developed for wireless
microphone systems. The UR195 re-defines the state of the art in
high end wireless microphone receivers.
The entire radio/audio system was designed from a “cold start,”
utilizing all that has been learned thus far. Many new types of IC’s
and semi-conductors are available now that were only ideas a few
years ago. The UR195 design takes advantage of these new devices.
UT195 TRANSMITTER
The UT195 hand-held transmitter design was the result of considerable research. The RF and audio performance of the transmitter was
considered first, followed by an analysis of the typical user’s needs
and the practicality of various design possibilities. The basic
circuitry had to accommodate any frequency in the VHF or UHF
spectrums. The mechanical design had to provide a comfortable
“feel,” yet be rugged, foolproof and easy to operate. The operating
features and functions faced several contradictions in the needs of
different types of users. This led to the development of a very
versatile design wherein the transmitter can be configured for either
“fool proof” operation or to provide user control of the audio level,
metering and indicators. The final UT195 design combines the
benefits of superior performance, ruggedness, user convenience, and
flexibility.
UM195 TRANSMITTER
The UM195 is a small belt-pack style transmitter which can be
clipped on the belt, slipped into a pocket, or even taped to the user's
body under clothing. It offers the same high performance and wide
deviation as the UT195 and is compatible with all of Lectrosonics'
195 series receivers. The UM195 comes with a standard lavalier
microphone but practically any mic can be adapted to work with this
transmitter. The transmitter audio level can easily be monitored and
set from the from panel.
DUAL-BAND COMPANDOR
Compandors have long been a source of audible distortion in
wireless microphone systems. The basic problem is that when the
full bandwidth of the audio signal is processed by a single
compandor, the attack and decay times will always be a compromise. If the time constants are fast, high frequency transient
distortion will be low, but low frequencies will be distorted. If the
time constants are slowed down, low frequency distortion will be
low, but high frequency transients will then be distorted. The 195
system introduces a new approach to solving this basic problem with
compandors, called “dual-band companding.”
There are actually two separate compandors in the 195 system, one
for high frequencies and one for low frequencies. A crossover
network ahead of the compandor separates the frequency bands at
1kHz with a 6dB per octave slope, followed by separate high and
low frequency compandors. The attack and release times in the high
frequency compandor are fast enough to keep high frequency
distortion at an extremely low level. The low frequency compandor
uses slower time constants, reducing low frequency distortion to
well below that of a conventional compandor.
75kHz DEVIATION
Wideband, 75kHz, of deviation improves the capture ratio, signal to
noise ratio, and AM rejection of a wireless system dramatically.
NO PRE-EMPHASIS/DE-EMPHASIS
The signal to noise ratio of the 195 system is high enough to
preclude the need for conventional pre-emphasis (HF boost) in the
transmitter and de-emphasis (HF roll off) in the receiver. Preemphasis and de-emphasis in an FM radio system usually provides
about a 10dB improvement in the signal to noise ratio of the system,
but the high frequency boost in the transmitter must be removed in a
purely complementary manner or else the frequency response of the
original audio signal will be altered.
Pre-emphasis can also cause distortion in the IF filtering stage in the
receiver, since the high frequencies have been boosted, which
increases the level of the harmonics in the FM signal. As this signal
is passed through the IF filters in the receiver, distortion can be
produced, most noticeable at full modulation. De-emphasis cannot
be applied until the signal is converted into audio, so there is no way
around this problem short of eliminating pre-emphasis altogether.
Neither of these problems occur in the 195 system. The dual-band
compandor in the 195 Series system essentially provides a dynamic
pre-emphasis/de-emphasis function with extremely low distortion.
EXCEPTIONAL THERMAL STABILITY
If temperature shifts cause the oscillators to drift, or values to
change in the detector, serious distortion will result. The components in the 195 Series systems meet very stringent tolerances for
thermal drift. System distortion in the 195 series remains at very
low levels over a very wide temperature range. This is especially
important in applications where the receiver and/or transmitter must
be operated near heat generating devices, outdoors in direct sunlight,
or with the receiver mounted in an equipment rack.
Rio Rancho, NM – USA
3
GENERAL TECHNICAL DESCRIPTION - UR195 RECEIVER
The UR195 is a high performance, dual-conversion, UHF receiver.
The RF performance is extremely stable over a very wide temperature range, making the UR195 perfectly suited to the rough environmental conditions found in the field. The proprietary audio
processing includes a dual-band compandor 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 connector. The audio output is calibrated for exact level
matching, with a ten LED bar graph meter.
SIX-POLE HELICAL RESONATOR FRONT-END
The UR195 utilizes a six-pole helical resonator for front-end
filtering. The helical resonators are custom manufactured in-house
to provide the high performance needed, yet still fit into the small
UR195 package. This outstanding front-end keeps the UR195 from
being affected by high power, adjacent RF signals and also provides
extremely high image rejection.
GaAs FET FRONT-END FILTER COUPLING
The UR195 utilizes an ultra low noise GaAs FET amplifier 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 UR195 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. This translates to the ability of the receiver to accept
higher input signals without overloading and causing distortion and
less cross talk between receivers in multiple system installations.
10 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. The 2nd IF
incorporates 2 more poles of filtering.
DIGITAL PULSE COUNTING DETECTOR
The UR195 receiver uses an advanced digital pulse counting
detector to demodulate the FM signal, rather than a conventional
quadrature detector. The most common problem with quadrature
detectors is thermal drift, particularly those that operate at higher
frequencies like 10.7 MHz. The UR195 design presents an elegantly
simple, yet highly effective solution to this age old problem.
The UR195 detector basically works like this: A stream of DC
pulses is generated at 455kHz. The pulse width is constant, but the
timing between pulses varies with the frequency shift of the FM
signal. The pulse stream is controlled by the FM signal coming
from the IF section which has been heavily limited. The average
voltage of the pulses within any given time interval varies in direct
proportion to the frequency modulation of the radio signal, producing the audio signal.
This type of detector eliminates the traditional problems with
quadrature detectors and provides very low audio distortion and no
thermal drift. The counting detector also adds additional AM
rejection, in addition to the limiting in the IF section. The amplitude
of the pulses is constant, so level differences in the IF signal do not
affect the pulse.
2:1 EXPANDER (Dual–Band Compandor)
This circuit is the other half of the dual-band compandor in a 195
system. “Dual-band Companding” is a closed loop system, that is,
whatever is done in the transmitter must be mirrored in the receiver.
The transmitter compresses the audio signal in two separate audio
bands using two separate time constants in order to avoid the
inevitable trade-offs in a single-band compandor. The companion
circuit in the receiver then re-expands this compressed signal
restoring the original dynamic range and frequency characteristics of
the signal.
LINEAR PHASE
470 - 608
MHz
HELICAL
RESONATOR
GaAS
FET
HELICAL
RESONATOR
CONTROLLED
OSCILLATOR
Figure 1 - UR195 Block Diagram
4
8 POLE
FILTER
10.7MHz IF
AMP
XTAL
1ST
HI-LEVEL
DIODE MIXER
455KHZ
BP
FILTER
2ND MIXER
&
IF AMP
XTAL
CONTROLLED
2ND
OSCILLATOR
MOD AUDIO
LED BARGRAPH METER
COUNTING
DETECTOR
AMP
32 kHZ
BLOCKING
FILTER
METER
MODE
32kHZ
AMP
2:1
EXPANDER
TREBLE
2:1
EXPANDER
BASS
PILOT
LED
PILOT
TONE
MUTE
AUDIO
AMP
ENABLE
PILOT
TONE
V+
DISABLE
MONITOR
LEVEL
AMP
OUTPUT LEVEL ADJUST
AND
RANGE SWITCH
HI
FIXED
HI
FIXED
MONITOR
OUT
XLR
OUT
3
1
2
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