Lectrosonics M187 Manuel utilisateur

M187

BELT-PACK TRANSMITTER

LECTROSONICS, INC.

Rio Rancho, NM

OPERATING INSTRUCTIONS

and trouble-shooting guide

TABLE OF CONTENTS

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

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

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

BATTERY REPLACEMENT ................................................................................. 6

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

MICROPHONE CORD TERMINATION ............................................................... 8

M187 INPUT JACK WIRING ................................................................................ 9

TROUBLESHOOTING ....................................................................................... 11

SPECIFICATIONS AND FEATURES ................................................................. 12

SERVICE AND REPAIR ..................................................................................... 13

RETURNING UNITS FOR REPAIR ................................................................... 13

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

INTRODUCTION

Thank you for selecting the Lectrosonics M187 transmitter. This transmitter repre-

sents over 70 years of combined experience in the design of RF devices and sets

new standards for operational convenience, flexibility and mechanical ruggedness.

The M187 transmitter features all metal construction and operates on high band

frequencies from 150MHz to 216MHz. The M187 was designed primarily for “belt-

worn” applications, however it works equally well for other applications and with

virtually any mounting configuration.

The M187 uses the microphone cord as the antenna, eliminating an unsightly

“dangling wire”. This transmitter may be used with a wide variety of audio sources.

The multi-pin input jack allows the use of “phantom powered” lavalier microphones

with either positive or negative bias voltages. The M187 will also match low imped-

ance dynamic microphones and high impedance inputs such as musical instruments

or tape decks.

Only the M187 transmitter is covered in this manual. Receivers are described in

separate manuals. The M187 operates with any Lectrosonics 187 Series VHF

receiver. A matched transmitter/receiver combination makes up a wireless “system”.

The M187 transmitter is FCC type accepted under the following Parts:

Part 90 (169-172 MHz) Part 74 (174-216 MHz)

Belt-Pack Transmitter

Rio Rancho, NM – USA

M187 Block Diagram

GENERAL TECHNICAL DESCRIPTION

The M187 transmitter is comprised of four major functional subsystems: the input compressor, the mic preamp/gain

control, the compandor, and the RF transmitter (see block diagram below).

The mic preamp is an ultra-low noise type op-amp. Aside from gain control, this stage also adds high frequency pre-

emphasis to the audio signal. This insures highest signal-to-noise ratios under varying signal conditions. Gain control

is semi-logarithmic to provide smooth gain control action.

The compandor is a high quality audio device that processes the input signal such that large dynamic ranges of input

signal can be transmitted to the receiver without overload or noise. A complementary system in the receiver recovers

the original dynamics of the signal for full audio quality. Compression and expansion ratios are complementary at 2:1.

High frequency pre-emphasis is implemented in the transmitter to provide another 10dB signal-to-noise ratio improve-

ment. Matching de-emphasis is provided in all receivers.

The compressor/limiter is a low distortion shunt FET compressor. Control signals for the compressor are derived

after the compandor to eliminate any possibility of overload under any signal condition up to a maximum of 3 Volts

input. The range of limiting action before gross distortion occurs is 35dB.

The compandor in the 187 series transmitters is much tighter than the 185 series. The H187 compandor will hold the

transmitter deviation to no more than ±15kHz under all circumstances. The 185 compandor would allow some

excursions beyond 15kHz during strong audio “spikes.”

The RF transmitter is composed of a crystal stabilized main oscillator followed by a frequency tripler and two fre-

quency doublers. All three stages are double tuned. Double tuning provides high attenuation of spurious signals,

which in turn minimizes the possibility that a transmitter would interfere with another transmitter/receiver system on

another frequency.

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.

Schematics and alignment instructions will be provided to qualified repair personnel upon request.

MIC PREAMP

LIMIT

LED

LEVEL

LED

COMPANDOR (VCO)

+9V IN

45MHZ 90MHZ 180MHZ

15 MHZ XTAL

OSCILLATOR

BATTERY

SENSOR

CIRCUIT

POWER

LED

FREQ.

TRIPLER

FREQ.

DOUBLER

VOLTAGE

REGULATOR

FEEDBACK

REGULATOR

FREQ.

DOUBLER

OUT

LIMITER

35 dB

CONTROLS AND FUNCTIONS

INPUT JACK

The input on the M187 accommodates virtually every lavalier, hand-held or shotgun microphone available. Use a

Switchcraft TA5F connector on the cord. See the separate sheet titled “M187 Input Jack Configuration” regard-

ing the correct connections for various microphones, and other sources.

ON/MUTE/OFF SWITCH

Turns the battery power on and off. The center position is an “audio mute”which should be used when setting the

MIC LEVEL control to turn off the sound from the microphone during this adjustment. When turning the transmitter

on, pause for a moment in the MUTE position to prevent a turn-on surge from occurring (a “thump”sound) in the

audio.

POWER ON/OFF LED

Glows brightly when battery is good. A weak or dim lamp means that the battery is weak, and has about an hour of

operation left (maybe a little more). If the lamp fails to light, the battery should be replaced. The power lamp should

light up in both the “mute”and “on”positions of the POWER/MUTE SWITCH.

The POWER LED is connected to a precision battery test circuit that continuously monitors battery voltage. The LED

is at full brightness with a new 9 Volt alkaline battery. As the battery voltage drops during use, the LED brightness will

also decrease. After 12 to 15 hours the battery voltage will be about 7 Volts and the LED will be completely out.

LECTROSONICS

M187

MUTE

OFF

LEVEL

LIMIT

MIC LEVEL

Belt-Pack Transmitter

Rio Rancho, NM – USA

Since the internal circuits are all tightly regulated and the RF output stage has a separate discrete regulator, the

transmitter will continue to operate to a battery voltage of 6.5 Volts. From 6.5 Volts to 6 Volts, the transmitter will still

operate, but with degraded performance. Please note that a weak battery will sometimes light the POWER LED

immediately after turn on, but will soon discharge to the point where the LED will go out, just like a flashlight with

“dead”batteries.

The combination of an accurate battery condition indicator and regulation of all internal circuits provides much longer

battery life, as well as consistent performance over the life of the battery.

MODULATION LEDS

Indicate the proper setting of the MIC LEVEL control.

LEVEL LED

Flickers or glows when sufficient audio is present.

LIMIT LED

Lights up when the audio volume level is high enough to cause limiting.

MIC LEVEL

Used to adjust the audio input level for the proper modulation.

ANTENNA

The microphone cord is used as the antenna. A dipole antenna is formed between the shield of the microphone cord

and the metal transmitter housing.

THE BELT CLIP

The belt clip may be removed for special applications by removing the two screws.

USE ONLY THE SCREWS THAT ARE SUPPLIED

The circuitry is tightly packed into this unit. Longer screws will permanently damage the transmitter!

BATTERY REPLACEMENT

The M187 transmitter is powered by a standard alkaline 9 Volt battery. It is important that you use ONLY an ALKA-

LINE battery for longest life. Standard zinc-carbon batteries marked “heavy-duty” or “long-lasting” are not ad-

equate. They will provide only about 4 hours of operation. Similarly, ni-cad rechargeable batteries only provide 4

hours of operation or less, and will also run down quite abruptly. Alkaline batteries provide about 15 hours of opera-

tion.

To open the battery compartment, press outward on the cover door in the direction of the arrow as shown in the

drawing. Only firm, sliding pressure is needed to open and close the battery door.

Swing the door open and take note of the polarity marked inside showing the location of the positive (+) and negative (-

) terminals. Insert the battery correctly and close the cover by pressing the door closed and across, reversing the

opening procedure illustrated above. Don’t force the door closed. The terminals will hit a protective polarity barrier.

You can see the large and small contact holes inside the battery compartment.

Press outward on the

battery door in this

direction

Swing the

door open

Belt-Pack Transmitter

Rio Rancho, NM – USA

OPERATING INSTRUCTIONS

1) Insert the microphone plug into the input jack, aligning the pins; be sure that the connector locks in.

2) Turn the power switch to the “MUTE”position on the transmitter. The “MUTE”position allows internal voltages to

stabilize before audio signal paths are opened.

3) Position the microphone in the location you will use in actual operation.

4) Keeping the power switch in the “mute”position, speak as loudly as you expect you will in normal system use.

Rotate the MIC LEVEL knob so that the LEVEL LED flickers or stays lit as you speak. The LIMIT LED should light

up on loud “peaks.”Occasional lighting of the LIMIT LED indicates proper operation and optimum signal-to-noise

ratio. Even when limiting is occurring, little or no distortion will occur, due to the high linearity of the limiting

circuitry in the M187. The input limiter will cleanly handle peaks up to 35dB above full modulation.

5) Set up the receiver according to the receiver manual.

6) Move the switch to the “ON”position on the transmitter, verify that the modulation LEDs indicate normally and

adjust the volume of the sound system, or the record level of your recorder.

NOTE:

Do not use the MIC LEVEL control to control the volume of your sound

system or the record level on your recorder. This control

should be set only as described in #4 above.

If the mic level is too high —the LIMIT LED will light will light frequently or stay on. This condition may cause distor-

tion.

If the mic level is too low —neither LED will light or the LEVEL LED will light dimly. This condition may cause hiss

and noise in the audio.

The LEVEL LED turns on at -10dB below full deviation. The LIMIT LED turns on at full deviation and indicates that

the input shunt compressor is operating. The input compressor operates over a full 35dB range regardless of the gain

control setting. The compressor uses a true absolute value circuit to detect both positive and negative peaks. The

attack time is 2 milliseconds and the release time is 80 milliseconds. Occasional limiting is desirable, indicating that

the gain is correctly set and the transmitter is being fully modulated.

MICROPHONE CORD TERMINATION

VIEW FROM SOLDER

SIDE OF PINS

0.3"

0.15" Heatshrink

Tubing

TA5F Connector Assembly

Mic Cord Stripping Instructions

Caution!

Do not allow the shield wire to touch any

metal part of the connector shell.

The shield wire is the antenna on VHF

models and poor operating range will result.

Shield Wire

Crimp

Tabs

Rubber

Insulation

Crimp

Tabs

Rubber

Insulation

Belt-Pack Transmitter

Rio Rancho, NM –USA

M187 INPUT JACK WIRING

The wiring diagrams shown on the attached sheet represent the basic wiring necessary for the most common types of

microphones and other audio inputs. Some microphones may require extra jumpers or a slight variation on the dia-

grams shown.

Caution - When wiring the connector, do not use the connector body for any electrical connections.

A common mistake is to use the connector body as an audio ground. The connector body is

already used as an RF ground and no other use is permitted.

It’s virtually impossible to keep completely up to date on changes that other manufacturers make to their products. It

is possible that you may encounter a microphone that differs from these instructions. If this occurs please call our toll-

free number listed in the back of this instruction manual. Our service department can answer your questions regard-

ing microphone compatibility.

When used on a wireless transmitter, the microphone element is in the proximity of the RF coming from the transmit-

ter. The nature of electret microphones makes them sensitive to RF, which can cause problems with the microphone/

transmitter compatibility. If the electret microphone is not designed properly for use with wireless transmitters, it will

be necessary to install a chip capacitor in the mic capsule or connector to block the RF from entering the electret

capsule. These types of modifications are not shown on the attached instructions.

The M187 uses the shield of the microphone cord as the antenna. Other brands use a “dangling wire”to emit the RF

from the transmitter. There is really no difference between these two approaches, with respect to the effect of the RF

on the microphone capsule. Even in transmitters that utilize a “dangling wire,”the microphone is still part of the

“ground plane”and is therefore still in the antenna circuit.

For answers to questions regarding microphone/transmitter compatibility, call our service manager or engineering

department at the factory.

PIN 1 Shield (ground) for positive biased electret lavalier microphones. Bias voltage source for negative biased

electret lavalier microphones. Shield (ground) for dynamic microphones and line inputs.

PIN 2 Shield (ground) for negative biased electret lavalier microphones. Bias voltage source for positive biased

electret lavalier microphones.

PIN 3 Low impedance microphone level input for dynamic microphones. Also accepts hand-held electret micro-

phones provided the microphone has its own built-in battery.

PIN 4 1K ohm source load for non-Lectrosonics electret microphones. Use in conjunction with other pins to provide

attenuation of high level input signals.

PIN 5 High impedance, line level input for tape decks, mixer outputs, musical instruments, etc.

Transmitter

Input Jack

LECTROSONICS

1uH

10K

510

60NH

330PF

185/187 Series

Transmitter Equivalent Input Circuit

5V Mic Bias

5mA max

To Mic Amp

POS BIAS (OR GND)

MIC

SOURCE LOAD

LINE IN

NEG GND (OR BIAS)

RF to Antenna

(mic cord)

RF BYPASSING

Some mics require RF protection to keep the radio signal

from affecting the capsule, even though the transmitter

input circuitry is already RF bypassed (see schematic

diagram).

If the mic is wired as directed, and you are having

difficulty with squealing, high noise, or poor frequency

response; RF is likely to be the cause.

The best RF protection is accomplished by installing RF

bypass capacitors at the mic capsule. If this is not

possible, or if you are still having problems, capacitors

can be installed on the mic wires inside the TA5F connector housing.

Install the capacitors as follows: Use 330 pF capacitors. Capacitors are available from Lectrosonics. Please specify

the part number for the desired lead style.

Leaded capacitors: P/N 15117 Leadless capacitors: P/N SCC330P

All Lectrosonics lavalier mics are already bypassed and do not need any additional capacitors installed for proper

operation.

BODY GROUND

Caution - When wiring the connector, do not use the connector body for any electrical connections. A common

mistake is to use the connector body as an audio ground. The connector body is already used as an RF ground on

VHF models and no other use is permitted.

LINE LEVEL SIGNALS

The normal hookup for line level signals is: Signal Hot to pin 5, Signal Gnd to pin 1, pin 4 jumped to pin 1, and pin 3

jumped to pin 1. This gives a 30dB attenuator that allows signal levels much higher than 3V to be applied without

distortion.

If more headroom is needed, insert a 100k resistor in series with pin 5. Put this resistor inside the TA5F connector to

minimize noise pickup.

If lower than normal line levels (less than 1V) are expected, use this hookup: Signal Hot to pin 5, Signal Gnd to pin 1,

and pin 4 jumpered to pin 1. This provides a 20dB attenuator allowing signals as high as 3V to be applied without

distortion.

WIRING HOOKUPS FOR DIFFERENT SOURCES

3 WIRE MIC2 WIRE MIC

CAPSULE CAPSULE

SHIELD

AUDIO

SHIELD

AUDIO

BIAS

TA5F

CONNECTOR

TA5F

CONNECTO

Preferred locations for bypass capacitors

Alternate locations for bypass capacitors

SHIELD

AUDIO

BIAS

WIRE ELECTRET MIC

POSITIVE BIAS

TA5F

PLUG

SHIELD

AUDIO

2 WIRE ELECTRET MIC

POSITIVE BIAS

TA5F

PLUG

SHIELD

BIAS

AUDIO

WIRE ELECTRET MIC

NEGATIVE BIAS

TA5F

PLUG

SHIELD

AUDIO

2 WIRE ELECTRET MIC

NEGATIVE BIAS

TA5F

PLUG

SHIELD

TIP

SLEEVE

LINE LEVEL

RCA or 1/4 " PLUG

AUDIO 1

TA5F

PLUG

DYNAMIC

MIC LEVEL

PIN PIN

SHIELD

Dynamic LO Z mic or electret with

manufacturers power supply.

TA5F

PLUG

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