Lectrosonics H175DC User Manual

H175DC

Plug-On Transmitter

OPERATING INSTRUCTIONS

and trouble-shooting guide

Digital Code Squelch

LECTROSONICS, INC.

Rio Rancho, NM

This page intentionally blank.

2

Plug-On Transmitter

INTRODUCTION

Thank you for selecting the Lectrosonics Professional Series wireless microphone
system.

This system represents well over 20 years of manufacturing experience in wireless
microphones, and almost 70 years of design experience. It is the best value avail­able today. You will find that the H175DC radiates more power than other standard
handheld wireless microphones. This provides both greater operational range, as
well as improved signal-to-noise ratio.

If you are new to wireless microphones, you will discover a new freedom of move­ment and convenience. If you are an experienced wireless user, you will be pleas­antly surprised with the effortless, quiet performance of the Lectrosonics Professional
Series design. Over time, you will appreciate the rugged dependability of the
H175DC. Superior mechanical design and construction mean years of trouble-free
use.

Only the H175DC transmitter is covered in this manual. A matched transmitter/
receiver combination makes up a “system.” Receivers are explained in separate
manuals.

The H175DC transmitter is constructed of metal and operates on interference-free
high band frequencies from 169 to 172MHz and 174 to 186MHz. Since the H175DC
uses the actual microphone case as an antenna, there is no need for any unsightly
extra wires. The H175DC plugs into the XLR jack of any hand-held microphone,
giving the user the greatest choice of mics.

TABLE OF CONTENTS

INTRODUCTION .................................................................................................. 3

GENERAL DESCRIPTION .................................................................................. 4

CONTROLS AND FUNCTIONS .......................................................................... 5

OPERATING INSTRUCTIONS ............................................................................ 6

BATTERY REPLACEMENT ................................................................................. 8

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

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

SERVICE AND REPAIR ..................................................................................... 11

RETURNING UNITS FOR REPAIR ................................................................... 11

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

H175DC series transmitters are FCC type accepted under the following Parts:

Part 90 (150-172 MHz)
Part 74 (174-216 MHz)

Rio Rancho, NM – USA

3

GENERAL DESCRIPTION

The H175DC is a “plug-on” transmitter that converts any microphone with an XLR connector to wireless operation.
The transmitter is comprised of four major functional subsystems: the mic preamp/gain control, the compandor, the
compressor/limiter and the RF transmitter (see block diagram below).

The digital code system provides much more reliable control over the receiver audio output than a conventional
squelch can provide. The transmitter generates a 9-bit code at turn on, and another code at turn off, to open and
close the audio output on the receiver. The squelch on the receiver cannot be opened by anything other than the
specific code it is programmed to receive. This superior squelch system is very necessary when the receiver is
connected into an automatic mixing system.

The input jack provides a phantom 5 Volts DC positive bias for all Lectrosonics’ electret lavalier microphones. Many
other electret microphones may be adapted to the H175DC Series by making wiring changes in the microphone
connector.

The mic preamp is an ultra-low noise type op-amp. Aside from gain control, this stage also adds high frequency pre­emphasis 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 RF transmitter is composed of the 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 source. 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 performance
consistent from the beginning (9 Volts) to the end (6.5 Volts) of battery life.

D.C.S.

MIC LEVEL

XLR

INPUT

LIMITER

35 dB

MIC

PREAMP

COMPANDOR

15MHZ XTAL

OSCILLATOR

(VCO)

BATTERY

SENSOR
CIRCUIT

FREQ.

TRIPLER

POWER
LED

45MHZ

FREQ.

DOUBLER

VOLTAGE

REGULATOR

90MHZ

FREQ.

DOUBLER

FEEDBACK

REGULATOR

180MHZ

RF

OUT

+9V IN

4