Lectrosonics R185 User Manual

R185

VHF RECEIVER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

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INTRODUCTION

Thank you for selecting the Lectrosonics system. The R185 represents over 80 combined years of experience in
the design of RF and audio devices, and sets new standards for RF performance and flexibility.

The R185 receiver was designed for professional users who demand outstanding performance and flexibility. It is a
single antenna, single channel design compatible with all Lectrosonics VHF 185 Series transmitters. The R185 may
be operated from 110V AC or from 12V DC, providing a high degree of versatility.

The R185 also functions as a receiver "module" for multi-channel receiver systems using 19 inch rack mounted
assemblies. Over 24 compatible frequencies are available allowing reliable, large-scale wireless stage productions
to run with no problems caused by cross-talk or intermodulation. RF/power distribution modules and 19" rack
mount assemblies are available to combine R185 receivers and simplify multi-channel installations.

Sharp filtering with minimal amplification in the front-end, narrow-band crystal filtering in the first IF stage, and a
double-balanced diode mixer all work together to provide extremely high selectivity, superb IM rejection, and very
high sensitivity. The end result of this design offers benefits for both the single channel and multi-channel user by
providing exceptional operating range and protection from interference.

TABLE OF CONTENTS

INTRODUCTION .......................................... 2

GENERAL TECHNICAL DESCRIPTION .......................... 3

RECEIVER FRONT PANEL ................................... 4

RECEIVER REAR PANEL .................................... 5

ANTENNA USE AND PLACEMENT ............................. 6

OPERATING INSTRUCTIONS ................................. 7

INDICATOR QUICK REFERENCE .............................. 7

TROUBLESHOOTING ....................................... 8

R185 REPLACEMENT PARTS and ACCESSORIES ................. 8

SERVICE AND REPAIR ..................................... 9

RETURNING UNITS FOR REPAIR ............................. 9

R185 SPECIFICATIONS AND FEATURES ........................ 10

WARRANTY ........................................ Back cover

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GENERAL TECHNICAL DESCRIPTION

6 SECTION

ACTIVE FILTERS SEPARATE

ANT

LC

FILTERS

IF AMP

2:1

SQUELCH

NOISE

AUDIO

0.5uV

HELICAL

RESONATOR

DBL BAL

DIODE
MIXER

6 POLE

HIGH FREQ

CRYSTAL

FILTER

FIRST

OSCILLATOR

DBL BAL

ACTIVE MIXER

SECOND

OSCILLATOR

DBL TUNED

DISCRIMINATOR

NOISE AND AUDIO

COMPLEMENTARY

EXPANDER

BALANCED

OUTPUT STAGE

The R185 receiver is comprised of five functional subsystems: the RF front-end, the double balanced mixer/local
oscillator, the first IF filter, the second IF filter and demodulator, the compandor and audio output section.

Figure 1 - R185 Block Diagram

The RF front-end consists of three cascaded pairs of helical resonators for high selectivity. Between the first and
second pair, and the second and third pair of helical resonators are low noise, grounded gate J-FET amplifiers.
These amplifiers are designed to provide only enough gain to make up for the loss through the helical resonators.
This combination of low front-end gain, coupled with the extremely high selectivity of the helical resonators prevents
overload in the mixer and provides exceptionally high image rejection, even with extremely strong RF signals.
Rejection of out-of-band signals is maximized, and intermodulation products are suppressed.

The first mixer stage consists of a high level, double balanced diode mixer. The oscillator is biased from a
regulated supply, yielding stable performance. The local oscillator crystal operates at approximately 16 MHz, and
can be adjusted above and below the nominal frequency in order to place the 21.4 MHz IF in the center of the
crystal filter’s narrow passband. The high selectivity of the crystal filter stage further minimizes the possibility of
interference from signals on adjacent frequencies.

The second IF filter and the audio demodulator, as well as the squelch and RF LED drive are provided by one
monolithic integrated circuit. The second IF filter is centered on 1MHz, and drives a double tuned quadrature type
FM demodulator. The squelch circuit is a supersonic noise detector type and is factory set for a -20dB SINAD level
(about .5uV). The squelch level is regulated and temperature compensated to maintain a consistent squelch level
under all conditions.

The compandor is driven by a multiple pole active low-pass filter. This filter ensures that supersonic noise will not
cause the compandor to increase gain incorrectly. The compandor senses the signal level, and dynamically
increases the gain for loud signals or decreases the gain for soft signals. In this way, the original dynamic range of
the transmitted signal is restored, while preserving a high signal-to-noise ratio. The expansion ratio is 2:1, which
produces a 2dB change in output level for a 1dB change in input level. In addition, the compandor has a de­emphasis network that is complementary to the pre-emphasis network in the transmitter.

2:1 1:2

COMPRESSION EXPANSION

+20dB
+10dB

0dB

AUDIO

SOURCE

-80dB

TRANSMITTER RECEIVER

RF LINK

100dB dynamic range

50dB dynamic range

100dB dynamic range

+20dB

+10dB

0dB

TO AUDIO

SYSTEM

-40dB-40dB

-80dB

Figure 2 - Compandor Action

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