Lectrosonics UT195 - Manual (Page 3)

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 consider­
able 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 compro­
mise. 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. Pre-
emphasis 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 compo­
nents 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.
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