Shure HF52 User Guide
222 HARTREY AVE., EVANSTON.
MICROPHONES AND ELECTRONIC COMPONENTS
AREA CODE 3121866-2200 CABLE: SHUREMICRO
TWX:
910-231-0048 TELEX: 72.4381
IL.
60204 U.S.A.
MODEL
HF52
MOBILE VOICE PICKUP SYSTEM
GENERAL
The Shure Model HF52 Mobile Voice Pickup System
is a dynamic unit designed specifically for
free" operation in a variety of mobile applications,
including police, taxicab, and other radio-dispatched
vehicles. When properly installed, the HF52 will provide high-quality communications without the need for
holding the microphone or hand-keying the transmitter.
The HF52 is designed for use only on vehicles with
12-volt negative ground electrical systems.
The HF52 consists of three assemblies: Model
HF52M Microphone, Model HF52A Amplifier, and Model
HF52S Footswitch. The microphone is supplied with a
mounting clip and a mounting bracket, both for use in
attaching the microphone to the vehicle sun visor, and
a cable for connecting to the amplifier. The amplifier,
which has an adjustable gain control for use with a
variety of mobile transmitters, is supplied with two
screws for attachment to the vehicle, and cables for
connection to the transmitter audio input and the vehicle 12 Vdc power. The weatherproofed normally
open, single pole footswitch is supplied with a perma-
nently mounted cable for connection to the transmitter,
and two screws for mounting to the vehicle floor. A kit
of cable clamps, clips and ties is provided to secure
the cables.
Features:
Convenient, hands-free operation under all conditions
=
Omnidirectional pickup pattern for uniform sound
output over wide range of microphone locations
.
Communications-type frequency response for cable C~~-~nectors.
maximum intelligibility 4. Connect red power cable with in-line fuse to
.
Amplifier suitable for use with most mobile trans-
mitter
carbon or transistorized microphones
=
Amplifier gain is adjustable for microphone distance and transmitter sensitivity
Virtually unaffected by
supply fluctuations and noise
Operable over wide temperature and humidity
range
.
tion
Before installing the HF52, place the amplifier and
footswitch in their approximate desired positions.
Determine whether connecting cables are of proper attach it to vehicle sun visor. Figure 1 shows mounting
length, and cut or splice them as required. If feasible,
connect the amplifier output cable and footswitch attachment. Note that either mounting device should
cable to the transmitter input connector before installing the amplifier and footswitch. when visor is in "up" position.
inputs designed
dynamic
Rugged withstands shock and vibra- mounted almost anywhere in the vehicle. However, for
Or
INSTALLATION
for
ceramic,
'ONTROLLED
RF
fields and power cable with cable clamps and screws or cable clips.
"hands-
high-imped-
Amplifier
Install the
1. Verify that vehicle battery is 12-volt negative
ground! i.e., negative battery cable is connected to
vehicle
2. Select mounting location for amplifier under
dashboard or on firewall, preferably left of steering
column. Make certain location does not interfere with
any vehicle control functions Or service access.
3. Drill two holes
(4Y4 in.) apart, and mount amplifier using two pan
head screws supplied.
to metal surface to provide chassis ground contact.
Be
certain
(covered by hole plug-see Figure
Also make certain that there is sufficient clearance to
allow insertion and removal of microphone and output
suitable 12-volt positive power SOUrCe. Source must
be controlled by ignition or transmitter power switch,
as HF52 does not contain its own power switch. Secure
power cable with cable clamps and screws (#32-0.116
in. drill) or cable clips.
5. Connect amplifier output cable and route to area
of transmitter audio input. Secure amplifier output
Microphone
The
sound equally from all directions. As such, it may be
maximum sound pressure and minimum outside noise
pickup, it should be located as close to the operator's
mouth as possible. A recommended method of installing the HF52M is as follows:
1. Select mounting clip or mounting bracket and
bracket attachment and Figure
be positioned at top of visor and away from driver
HF52A Amplifier as follows:
frame.
(#29-0.136 in.) spaced 108 mm
NOTE:
that
access
HF52M is an omnidirectional unit, receiving
Make sure screws attach
to
gain
control
2
shows mounting clip
in
7)
is maintained.
amplifier
I
Copyright
27A1659
1981,
(UC)
Shure Brothers
Inc.
Printed
in
U.S.A.
2. Snap microphone into mounting clip or bracket.
Microphone should face roof of vehicle with visor in
"up" position. When visor is moved down, microphone
on visor faces downward.
MICROPHONE IN MOUNTING BRACKET
FIGURE
MICROPHONE IN MOUNTING CLIP
FIGURE
3. Secure microphone cable at visor hinge using
cable tie.
4. Route cable down between driver's door and
windshield to amplifier.
design make it. necessary for the installer to decide
the best method of routing the cable. Cable clamps
and screws
cable.
5. Connect microphone to amplifier.
On some vehicles, it may be desirable to mount the
microphone on the steering column. When this mounting method is appropriate, secure the mounting
bracket with a strong rubber band passed around the
steering column and hooked to both sides of the microphone clasp on the mounting bracket. The clasp
should be rotated on the bracket so that the micro-
phone faces the vehicle operator. Route and secure
the cable conveniently as described in step 4 above.
Connect the microphone to the amplifier.
(#32-0.116 in. drill) are provided to secure
1
2
NOTE: Variations in vehicle
Footswitch
Install the HF52S Footswitch as follows:
1. Locate footswitch on floorboard in an area that
will permit easy access when operated by driver's left
foot. For vehicles with automatic transmissions, optimum location is to left and slightly above brake pedal.
2. Drill two holes
(3 in.) apart, and attach footswitch to floorboard using
two pan head screws supplied.
3. Run footswitch cable to area of transmitter audio
input. Secure footswitch cable with cable clamps and
screws
(#32-0.116 in. drill) or cable clips.
(#29-0.136 in.) spaced 76.2 mm
Transmitter Connections
Obtain an input connector for the transmitter to
be used, and wire the amplifier output leads to the
transmitter audio input (shield to ground). Wire the
footswitch (normally open) leads across the transmitter
keying circuit. Note that the footswitch is not directly
connected to the amplifier.
Adjustments
Remove the hole
control (see Figure 7). With a small screwdriver, turn
the amplifier gain control fully counterclockwise. Start
the engine and key the transmitter while sitting in the
driving position and talking at a normal level. Advance
the amplifier gain control until proper transmitter
modulation is obtained. To avoid excessive noise pickup, do not set the gain control higher than necessary
for full voice modulation. Replace the hole plug.
plug covering the amplifier gain
Low- and High-Frequency Rolloff
The normal frequency response of the HF52A Amplifier is shown in curves 4-5 of Figure 6. The
quency rolloff characteristic shown provides optimum
intelligibility under conditions of high background
noise. When background noise is not a problem, the
amount of low-frequency
shown in curves 1-3. The low- and high-frequency
off characteristics of the Amplifier may be changed as
shown in curves 1-3 and 6-8 of the figure by a simple
capacitor substitution as follows.
Remove the Amplifier cover by removing the four
screws securing it to the box. To change the
frequency rolloff, place a 25 Vdc minimum capacitor
across terminals A and
Curve 1:
Curve
Curve
Curve
Restricting the high-frequency response may also,
under some conditions, reduce the effect of background noise. To change the high-frequency
solder a capacitor (25 Vdc minimum) of the following
value across printed circuit board terminals G and H
(placing this value in parallel with capacitor C3):
Curve
Curve 6:
Curve 7: .0047
Curve 8: .O1
Replace and secure the Amplifier cover.
NOTE: The resultant system response (microphone
and amplifier) is shown in Figure 8.
,068 pF
2:
.027 pF
3:
.O1 pF
4:
none (as supplied)
5:
none (as supplied)
.0015 pF
rolloff can be reduced as
J
of the printed circuit board:
pF
pF
low-fre-
roll-
low-
rolloff,
OPERATION
The HF52M Microphone is an omnidirectional unit,
designed for minimum wind and vibration pickup.
When properly installed and adjusted, the HF52 system
(microphone and amplifier) will provide approximately
the same output level at approximately 46 cm (18 in.)
as a "close-talked" communications microphone. The
acoustical elements are designed to optimize performance in the frequency range of 200 to 5,000 Hz. This
results in the substantial reduction of sounds outside
the desired range.
Because the microphone is located at a distance
from the operator, its output is relatively low and requires amplification. The required gain is supplied by
the
HF52A Amplifier. Therefore,
ciently high level and within the microphone frequency
range will be transmitted. This means that the operator
should be as close as possible to the microphone for
maximum voice pickup and minimum noise pickup.
However, it is not necessary for the microphone to be
pointed
is satisfactory, as long as the microphone is as close
as possible to the operator.
at
the operator; any microphone orientation
all
sounds of suffi-
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