Lectrosonics UT195 User Manual download pdf (Page 4)

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 tempera-

ture range, making the UR195 perfectly suited to the rough environ-

mental 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, produc-

ing 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.

HELICAL

RESONATOR

GaAS

FET

470 - 608

MHz

XTAL

CONTROLLED

1ST

OSCILLATOR

8 POLE

LINEAR PHASE

FILTER

455KHZ

FILTER

10.7MHz IF

AMP

2ND MIXER

IF AMP

COUNTING

DETECTOR

32 kHZ

BLOCKING

FILTER

HI-LEVEL

DIODE MIXER

XTAL

CONTROLLED

2ND

OSCILLATOR

2:1

EXPANDER

TREBLE

2:1

EXPANDER

BASS

AUDIO

AMP

MONITOR

OUT

OUTPUT LEVEL ADJUST

AND

RANGE SWITCH

XLR

OUT

PILOT

TONE

MUTE

HELICAL

RESONATOR

AMP

DISABLE

PILOT

TONE

MOD AUDIO

LED BARGRAPH METER

AMP

PILOT

LED

AMP

ENABLE

32kHZ

V+

MONITOR

LEVEL

METER

MODE

FIXED

Figure 1 - UR195 Block Diagram

1 2 3 4 5 6 7 8 9 10 11 12

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Lectrosonics UT195 User Manual Page 4

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