Lectrosonics M187 User Manual
M187
BELT-PACK TRANSMITTER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM
INTRODUCTION
Thank you for selecting the Lectrosonics M187 transmitter. This transmitter represents 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 “beltworn” 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 impedance 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”.
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
The M187 transmitter is FCC type accepted under the following Parts:
Part 90 (169-172 MHz) Part 74 (174-216 MHz)
2
Belt-Pack Transmitter
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 improvement. 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 frequency 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.
1
2
3
4
5
LIMITER
35 dB
MIC PREAMP
LEVEL
LED
LIMIT
LED
COMPANDOR
+9V IN
15 MHZ XTAL
OSCILLATOR
(VCO)
BATTERY
SENSOR
CIRCUIT
FREQ.
TRIPLER
POWER
LED
45MHZ 90MHZ 180MHZ
FREQ.
DOUBLER
VOLTAGE
REGULATOR
FREQ.
DOUBLER
FEEDBACK
REGULATOR
RF
OUT
M187 Block Diagram
Rio Rancho, NM – USA
3
CONTROLS AND FUNCTIONS
LECTROSONICS
M187
ON
MUTE
OFF
LEVEL
LIMIT
MIC LEVEL
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.
4
Belt-Pack Transmitter
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!
Rio Rancho, NM – USA
5
Loading...