Lectrosonics T187 User Manual

T187

VHF HAND-HELD TRANSMITTER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

INTRODUCTION

Thank you for selecting the Lectrosonics T187 hand-held wireless transmitter. The
T187 combines over 80 years of engineering experience with the very latest compo­nents in a design that addresses the most demanding professional applications.

The design of the T187 was the direct result of numerous conversations with users,
staging and touring companies and dealers across the US. The specific concerns
and needs brought up in these conversations led directly to the development of the
operational features offered on the T187. This is certainly not the first hand-held
transmitter ever designed, but it is definitely the most thoroughly engineered unit
available.

The T187 is an integral microphone/transmitter with an internal antenna. The
antenna is a dipole type utilizing the two printed circuit boards as the elements. The
housing is composed of durable PVC, machined to a natural, comfortable shape.
Internal mechanical parts are machined aluminum.

Only the T187 transmitter is covered in this manual. Companion receivers are
covered in separate manuals. The T187 will operate with any 185 Series Lectroson­ics VHF receiver on the same frequency.

TABLE OF CONTENTS

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

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

CONTROLS AND FUNCTIONS .......................................................................... 4

BATTERY INSTALLATION ................................................................................... 7

OPERATING INSTRUCTIONS ............................................................................ 8

OPERATING NOTES ........................................................................................... 8

TROUBLESHOOTING ......................................................................................... 9

SERVICE AND REPAIR ..................................................................................... 10

RETURNING UNITS FOR REPAIR................................................................... 10

SPECIFICATIONS AND FEATURES ................................................................ 11

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

The T187 wireless microphone is FCC type accepted under the following parts:

Part 90 (150-172 mHz) and Part 74 (174-216 mHz)

2

VHF Hand-held Transmitter

GENERAL TECHNICAL DESCRIPTION

The T187 transmitter is comprised of a number of functional sub-systems as shown in the block diagram below. It is
offered with a variety of popular dynamic and electret microphone capsules from Shure, Electro-Voice and others for
various applications.

The limiter is a low distortion shunt FET compressor operating before the mic preamp. Control signals for the
compressor are derived after the mic preamp to eliminate any possibility of overload under any signal input condition
up to a maximum of 30 Volts input. The range of limiting action before distortion occurs is 20 dB. Audio signal level
and compressor action are indicated by LEDs visible under the battery cover door, next to the gain control.

The mic preamp is an ultra-low noise NE5534 type op-amp. The gain control, accessed by removing the battery
door, is semi-logarithmic to provide smooth action. Aside from gain control, this stage also adds high frequency pre­emphasis to the audio signal, to provide a 10 dB signal-to-noise ratio improvement. The receiver provides matching
de-emphasis to insure the highest signal-to-noise ratios under varying RF signal conditions.

The T187 audio section includes a 2:1 compandor noise reduction circuit compatible with all Lectrosonics 185 Series
VHF receivers. This compandor compresses (“encodes”) the dynamic range by reducing it 2:1 in the transmitter
audio signal. Complementary circuitry in the receiver restores (“decodes”) the original full dynamic range of the
signal by expanding it 1:2.

There are two operating switches located on the bottom panel. One is for power on/off and the other is an audio
mute. These operating switches can be bypassed for applications where the user should not have access to them.

The RF transmitter section is composed of a crystal stabilized main oscillator followed by a frequency tripler and two
frequency doublers. The crystal controlled frequency is extremely stable over a wide temperature range and over
time. All three oscillator stages are double tuned. Double tuning provides higher attenuation of spurious emissions
which, in turn, minimizes the possibility that the transmitter RF output would interfere with another transmitter/
receiver system operating in the same vicinity.

All RF stages are biased from a regulated internal power supply. The output stage has a separate feedback regula­tor which not only stabilizes its operating point, but also minimizes AM distortion. These regulators keep the RF and
audio performance consistent from the beginning (9 Volts) to the end (6.5 Volts) of battery life.

LIMIT
LED

MIC

CAPSULE

LIMITER

PRE
AMP

BATTERY

9 VOLT

-10dB
LED

COMPANDOR

+9V OUT

AUDIO

BYPASS

BYPASS

POWER

OSC.

(VXO)

+9V IN

TRIPLER

BATT

SENSOR

POWER

LED

ON/OFF

DOUBLER

VOLTAGE

REGULATOR

INTERNAL
ANTENNA

DOUBLER

FEEDBACK

REGULATOR

T187 Block Diagram

Rio Rancho, NM – USA

3

CONTROLS AND FUNCTIONS

EXTERNAL

“P” SWITCH -- POWER ON/OFF

A slide switch which turns battery power on and off. The LED next to the switch lights up when the
“P” switch is turned on. This LED also serves as a battery condition indicator. The LED will glow
brightly when the battery is good and will dim as the battery condition deteriorates. The LED is at
full brightness with a new battery. After 12 to 15 hours of operation the battery voltage will be about
7 Volts and the LED will be completely dark.

“A” SWITCH -- AUDIO ON/OFF

A slide switch which “mutes” the audio in the OFF position and allows the audio gain (modulation
level) of the transmitter to be adjusted without feedback from the sound system.

INTERNAL

MOD LEVEL LEDs

These LEDs indicate the audio input level and are used when adjusting the
transmitter AUDIO LEVEL (gain) control. As the audio level increases, first one
LED lights. The other LED lights as the audio level reaches maximum modula­tion. The LEDs are located underneath the battery cover, next to the AUDIO
LEVEL control.

AUDIO LEVEL

This knob (located underneath the battery door) is operated while speaking or
singing into the transmitter to adjust the audio gain of the T187 for the correct
amount of modulation. The LEDs located next to it indicate the modulation level as the gain is adjusted. See page 8
for details on this very important adjustment.

Audio Power

On/Off On/Off

Mod Level

LEDs

Gain Control

AUDIO
LEVEL

PA

EXTERNAL SWITCHES BYPASS

This concealed slide switch defeats the external switches on the bottom panel for
applications where it is best that the user not be able to operate the power and
mute switches.

EXTERNAL

EXTERNAL

LED

SWITCHES

OFF

BYPASS

Bypass Switches

EXTERNAL LED OFF

This slide switch defeats the battery status LED on the bottom panel for applications where the LED may be distract­ing. With this switch in the right-hand position, the power will remain on and the transmitter operating, even though
the power LED is off.

4