Comtek M-175 User manual

M-175 OPERATOR’S MANUAL
357 West 2700 South • Salt Lake City, Utah 84115 • Phone: [phone] • Fax: [phone] • http://www.comtek.com
M-175
Personal
Communication
Transmitter

© 2012 COMTEK®All rights reserved.
Printed in the U.S.A. 01-16-12
TABLE OF CONTENTS
Introduction ...........................................................
Setup ...............................................................................
Controls ..................................................................
Battery Removal / Replacement ......................................
Battery Charging ......................................................
Auxiliary Audio Input Operation ...................................
Snap-On Belt Clip .................................................
Frequency Selection ...............................................
Frequency Information ..........................................
P-7 Option ..............................................................
Optional Accessories ...............................................
Trouble Shooting .....................................................
Specifications .........................................................
Warranty and Service ..................................................
1
2
3
4
5
6-7
7
8
9-10
11
12
13-14
15
16

INTRODUCTION
Page 1
The M-175 personal
transmitter is a
professional
quality, compact
body-worn transmitter
designed for reliable one-way
remote communication. It’s ideal for many
applications including: personal cueing, assistive listening, tour guide
presentations, communication for on-the-job training, (requiring being
some distance away or in a noisy environment), and other personal,
one-way remote communication situations.
For a natural sound, this transmitter incorporates the latest digital and
analog technologies to produce high quality sound with low residual
noise, wide dynamic range and extended frequency response.
The audio processing circuit allows a choice of companded 2:1 audio
processing when used with Comtek full fidelity receivers, or
non-companded 1:1 audio processing on prescribed channels with
Comtek and other lower cost popular receivers. Both audio processing
systems have the same frequency response of 80 Hz to 10 KHz.
Operating under F.C.C. Regulation Part 90, the M-175 transmitter
has greater transmission range and reliability.
M-175
Personal
Communication
Transmitter

Setup
a. Check to ensure that the M-175 transmitter’s radio frequency channel is
the same as the associated COMTEK receiver’s channel. (Channels are
indicated by the rotary channel selector switches on the back of the
transmitter. See page 8.)
b. Open the battery door cover on the transmitter (see page 4) and
insert a new nine volt alkaline battery (Eveready E522 or equivalent). This
type of battery will offer up to 14 hours of operation. Replace the battery before
every use if the demand for fail-safe operation outweighs battery cost. The use of
carbon batteries is not recommended.
NOTE: If a rechargeable battery is to be used, ensure that it has been
allowed to charge at least twelve hours to bring it to full charge
(see page 5 for battery charger instructions).
c. Connect the microphone to the transmitter by inserting the microphone
plug into the receptacle on the top of the transmitter. The transmitter is
operating when the transmitter power switch is turned on and the battery
status/on indicator illuminates.
NOTE: The 48-inch microphone cord also functions as part of the
transmitter’s antenna system. For optimum performance, this cord
should be fully extended. Coiling or bunching the microphone
cord may reduce the range of the transmitter. The transmitter
should be carried by the snap-on belt clip (included) or in a pocket
or belt-clip pouch.
d. In a situation where an extremely loud voice or a very soft voice is used, it
is necessary to adjust the audio input gain control while observing the audio
“voice” level modulation indicator. A full bright LED indicates full audio
compression at 100% modulation. For best performance, the audio input
gain should be adjusted for some low level LED luminescence during
normal audio levels with occasional full bright peaks indicating 100%
modulation.
M-175 SETUP
Page 2

Page 3
M-175 CONTROLS
nCHANNEL SWITCHES: These rotary switches are used to set
the transmitter to the desired operating frequency.
(See page 9 and 10 for frequency selection chart.)
oBATTERY COMPARTMENT: The battery
compartment features a hinged battery cover and
an alignment system that ensures proper battery
polarity. Battery installation and removal is
facilitated by simply manipulating the bottom of
the battery.
pAUXILIARY AUDIO INPUT JACK:
Allows transmitter to use line level,
earphone level, or fixed AUX as an audio
source.
qAUDIO “VOICE” MODULATION
INDICATOR: This indicator is used in
making adjustment with the Audio Input
Gain Control.
rMIC / ANTENNA JACK: This jack accepts an
electret type microphone having a 48” long cord with a
micro-mini 2.5 mm mono plug. The microphone cord
functions as part of the transmitter’s antenna system and
must be in place for auxiliary audio input operation. If
microphone function is not necessary, the optional
microphone switch should not be on for this operation.
sPOWER / BATTERY STATUS INDICATOR: This
LED indicator will illuminate continuously when the unit is
on indicating normal operation. When the battery voltage drops below 6 volts, the LED
will flash rapidly, indicating that a new battery is needed.
tOPTIONAL MIC SWITCH: This switch turns off the microphone without turning off
the transmitter carrier.
uAUDIO INPUT GAIN CONTROL: This is a microphone and AUX level input gain
control. This control is used with the “Voice” modulation indicator.
vON / OFF SWITCH: This switch turns the transmitter on and off.

Page 4
Low Battery Indicator
The LED on the top of the transmitter
indicates the status of the battery as
well as indicating that the unit is turned
on. When the transmitter is turned on,
the LED illuminates. If the battery is low,
the green LED will blink rapidly to warn
you that the battery will soon be dead.
Replace a low battery immediately.
M-175 BATTERY REMOVAL / REPLACEMENT
Pull back battery door latch and allow battery
cover door to spring open. To remove battery,
simply manipulate the bottom of battery out of
the compartment and remove.
To insert battery, face battery
with negative terminal in line with
large hole in battery compartment,
press battery into compartment and close
battery door until it snaps shut. Note: It is not
possible to put battery in backwards.
Battery indicator LED
Battery Removal / Replacement

Page 5
M-175 BATTERY CHARGING
Battery Charging
1. Make sure that a seven cell 9 volt Ni-MH rechargeable
battery is used with a minimum of 200 mAh capacity.
(Alkaline batteries must not be charged.)
2. Make sure the M-175 is turned OFF.
3. Note that the red charging indicator on the charger is ON when the M-175
is plugged into the charger through the audio output jack.
4. When using the NBC 9-2C charger allow the battery to charge for 14 hours
for a full charge. Unit must then be unplugged. When using the
NBC 9-3-1 digital fast charger the charger will automatically end the
charge cycle and the red LED will change to green. With the NBC 9-3-1
charger the unit may be left in the charger until the unit is used.
5. Periodically open the battery compartment on stored COMTEK units to
check for battery leakage. If a battery is leaking, it must be discarded,
and the battery compartment must be cleaned or returned to COMTEK’s
service department for repairs.
IMPORTANT
NBC 9-2C
14-hour charger
NBC 9-3-1
digital fast charger

Page 6
M-175 AUXILIARY AUDIO INPUT OPERATION
Auxiliary Audio Input Operation
The M-175 transmitter may transmit from a variety of audio sources such as
digital media players, or any audio device having an auxiliary or earphone
level audio signal.
The auxiliary input cable supplied with the M-175
transmitter (CB-36 ST) will operate with any device
having a mini 3.5 mm jack, stereo or mono, and
with line level or earphone level output.
To accommodate a variety of specialty
applications, auxiliary input cables
with RCA phono plug, 1/4” audio
phone plug, and XLR connectors are
available from COMTEK.
Setup
a. Connect the microphone
to the transmitter by
inserting the microphone
plug into the receptacle on
the top of the transmitter.
Note: The microphone
cord functions as part of the
transmitter’s antenna system
and must be in place for auxiliary
audio input operation. If microphone
function is not necessary, the optional microphone
switch should not be on for this operation.
b. Connect the proper auxiliary input cable to the audio source. Connect the
right-angle mini plug end of the auxiliary input cable into the “AUX” input
jack of the M-175 transmitter.
Note: Check to ensure that the audio source is a line level, earphone level,
or fixed AUX level output.

Page 7
Belt clip installation
M-175 SNAP-ON BELT CLIP (Included)
Belt clip removal
c. Turn on the transmitter with program from the audio source being fed to
the transmitter. Observe the audio “voice” level modulation indicator. A full
bright LED indicates full audio compression at 100% modulation. For best
performance, the audio input gain should be adjusted for some low level
LED luminescence during normal audio levels with occasional full bright
peaks indicating 100% modulation.
d. When using the auxiliary audio input with the microphone plugged into
the transmitter, priority should be given to the microphone gain adjustment.
The mixing balance between the auxiliary audio and the microphone should
be made with the volume control of the auxiliary audio source.
Note: The optional microphone switch only affects the
microphone. It does not affect the auxiliary audio input.
M-175 AUX OPERATION (Cont.) / SNAP-ON BELT CLIP
STEP 1:
Hook belt clip
retaining lip over
front case ridge.
STEP 2:
Rotate belt clip down onto case. Apply
pressure on both sides of clip, snapping
clip retainers into slots.
Clip retainer
Retainer slot Belt clip removal indent
Flex out and pull down with your
thumb or a large coin (quarter) to
unsnap belt clip from case.

Page 8
Frequency Selection (72-76 MHz)
The M-175 transmitter can operate on one of 88 available channels
between 72-76 MHz. COMTEK channel designations indicate both
standard non-companded channels and high-fidelity companded channels.
Channels 1-88 are to be used only with receivers having 2:1 audio
companding processing. Channel position 91-00 is to be used only with
receivers having linear non-companded audio processing. COMTEK
transmitters automatically transmit the proper modulation when set to
either number channels 1-88 or channels 91-00 (A-J).
After you have determined the channel on which
you are going to operate, position the two rotary
switches to indicate the channel. The left
rotary switch is for tens and the right rotary
switch is for ones, e.g. to select channel 41
(72.92 MHz), position the left rotary switch
to point to 4 (X10), and position the right
rotary switch to point to 1 (X1). Refer to frequency charts
on pages 9 and 10 for selectable frequencies.
Multiple Channel Operation
When multiple transmitters are broadcasting in the same immediate area
(within 100 feet), the RF signals will “mix” together generating additional
signals. If these product frequencies are too close to a frequency which you are
using, you will experience intermodulation interference. This condition is
common to all radio receivers to some extent.
Simultaneous operation of more than three channels requires frequency
coordination to avoid intermodulation interference which could result in
poor or unusable performance.
To avoid this type of interference, you should select frequencies from one of
the standard groups (see group frequency charts on pages 9 and 10), or use
COMTEK’s frequency selection software available at www.comtek.com to
determine appropriate frequencies or contact COMTEK to obtain a free copy.
M-175 FREQUENCY SELECTION

CHAN FREQ
Page 9
M-175 FREQUENCY INFORMATION
GROUP 1
GROUP 2
GROUP 3
CHAN FREQ
72.02 MHz
72.22 MHz
72.72 MHz
74.61 MHz
75.62 MHz
75.72 MHz
01
11
31
45
70
75
CHAN FREQ
72.08 MHz
72.18 MHz
72.72 MHz
74.77 MHz
75.58 MHz
75.92 MHz
04
09
31
53
69
85
CHAN FREQ
13
25
54
57
81
87
72.26 MHz
72.58 MHz
74.79 MHz
75.25 MHz
75.84 MHz
75.96 MHz
Transmitter Proximities For Multiple
Channel Operation
Frequency groups being transmitted should
be separated by 2X the operating area;
and for best performance, the group
operating areas should have a 100 ft.
minimum separation.
transmitters
Group 2
operating area
transmitters
transmitters
Group 1
operating area
Group 3
operating area
Transmitter
separation
Transmitter
separation
72-76 MHz
STANDARD
COMPANDED CHANNELS
CHAN FREQ
72.02 MHz
72.04 MHz
72.06 MHz
72.08 MHz
72.10 MHz
72.12 MHz
72.14 MHz
72.16 MHz
72.18 MHz
72.20 MHz
72.22 MHz
72.24 MHz
72.26 MHz
72.28 MHz
72.30 MHz
72.32 MHz
72.34 MHz
72.36 MHz
72.38 MHz
72.40 MHz
72.42 MHz
72.46 MHz
72.50 MHz
72.54 MHz
72.58 MHz
72.62 MHz
72.64 MHz
72.66 MHz
72.68 MHz
72.70 MHz
72.72 MHz
72.74 MHz
72.76 MHz
72.78 MHz
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
CHAN FREQ
72.80 MHz
72.82 MHz
72.84 MHz
72.86 MHz
72.88 MHz
72.90 MHz
72.92 MHz
72.94 MHz
72.96 MHz
72.98 MHz
74.61 MHz
74.63 MHz
74.65 MHz
74.67 MHz
74.69 MHz
74.71 MHz
74.73 MHz
74.75 MHz
74.77 MHz
74.79 MHz
75.21 MHz
75.23 MHz
75.25 MHz
75.27 MHz
75.29 MHz
75.31 MHz
75.33 MHz
75.35 MHz
75.37 MHz
75.39 MHz
75.42MHz
75.46 MHz
75.50 MHz
75.54 MHz
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
CHAN FREQ
75.58 MHz
75.62 MHz
75.64 MHz
75.66 MHz
75.68 MHz
75.70 MHz
75.72 MHz
75.74 MHz
75.76 MHz
75.78 MHz
75.80 MHz
75.82 MHz
75.84 MHz
75.86 MHz
75.88 MHz
75.90 MHz
75.92 MHz
75.94 MHz
75.96 MHz
75.98 MHz
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
Automatic
Non-Companded
Channels
91
92
93
94
95
96
97
98
99
00
72.1 MHz
72.3 MHz
72.5 MHz
72.7 MHz
72.9 MHz
75.5 MHz
75.7 MHz
75.9 MHz
74.7 MHz
75.3 MHz

Page 10
M-175
LETTER CHANNELS
(72-76 MHz)
CHANNEL FREQUENCY
91
95
98
00
A 72.1 MHz
E 72.9 MHz
H 75.9 MHz
J 75.3 MHz
GROUP 1
CHANNEL FREQUENCY
92
97
99
B 72.3 MHz
G 75.7 MHz
I 74.7 MHz
CHANNEL FREQUENCY
93
96
C 72.5 MHz
F 75.5 MHz
GROUP 2
GROUP 3
CHANNEL FREQUENCY
91
92
93
94
95
96
97
98
99
00
A 72.1 MHz
B 72.3 MHz
C 72.5 MHz
D 72.7 MHz
E 72.9 MHz
F 75.5 MHz
G 75.7 MHz
H 75.9 MHz
I 74.7 MHz
J 75.3 MHz
Standard
Non-Companded
Channels
(For PR-72b and PR-75)
Note: Although the same frequencies appear in the companded and
non-companded frequency charts, non-companded channels should not
be used with companded receivers.
In order to accommodate a greater variety of receivers, the M-175 transmitter
incorporates the option to operate with receivers that have companded or
non-companded audio processing. However, the M-175 transmitter must
operate non-companded with non-companded receivers and companded
only with receivers that incorporate companding processing. A mismatch
will result in unacceptable audio performance.
Basic Companding Theory
The dynamic range of the audio signal is compressed in the transmitter at a
2:1 ratio. The receiver then expands the audio signal at a complementary
1:2 ratio to restore the dynamic range of the audio signal to the original level
and also to provide additional noise reduction when no audio signal is
present.
M-175 FREQUENCY INFORMATION (Continued)

MBS-216 Mounting Bracket
The optional MBS-216 mounting-bracket stand is
an ideal way to conveniently position the M-175
Option P-7 transmitter for field use. The M-175 clip
snaps into the mounting bracket locking the
transmitter in place. The MBS-216 maintains a
vertical antenna position, maximizing the
performance of the M-175 Option P-7 transmitter.
MBS-216
mounting bracket
stand
Included
belt clip
Auxiliary
audio
input
jack
BNC
type
connector
FWA-72TL
short top
loaded whip
antenna
M-175 P-7 OPTION
Page 11
FWA-72TL Antenna
This short, top-loaded, omnidirectional antenna minimizes the size of
the antenna required to operate in the VHF frequency range of 72-76 MHz.
In order to maintain good propagational efficiency, this type of antenna
has limited bandwidth. Two separate antennas must be used to cover
the two operating frequency ranges of 72-73 MHz (antenna #1) and
74 to 76 MHz (antenna #2). Both antennas are supplied with the M-175
Option P-7 transmitter.
CB-36 XLR
(supplied)

Page 12
Optional Accessories
1. NBC 9-2C Battery charger
2. NBC 9-3-1 Digital fast charger
3. NBC 9-3-12 Digital 12-station fast charger
4. NH9-200 Rechargeable batteries
5. BC-216 Snap-on belt clip
(supplied with M-175)
6. P1 Universal pouch
7. SM-185 Unidirectional
electret condenser
microphone
8. PSC-HM Headworn
unidirectional electret
microphone
Auxiliary Audio Input Cords
9. CB-36 STM Stereo mini 3.5 mm
(supplied with M-175)
10. CB-36 RCA Phono plug
(optional)
11. CB-36 ST1/4 Stereo 1/4”
(optional)
12. CB-36 XLR XLR-F 3 pin connector
(optional)
M-175 OPTIONAL ACCESSORIES

Page 13
Batteries and Battery Charging
If...
Test indicator lamp doesn’t illuminate when units are turned on...
Then...
• If rechargeable batteries are used, ensure that they have been allowed to
charge at least 14 hours to a full charge. Verify that the charging indicator
lamps are illuminated when the charging plugs are plugged into the units.
The units’ power switches must be in the “off ” position for charging.
• If the test indicator lamp still does not illuminate after a full charge, verify
that the system is operational by using a new alkaline battery. If the system
is operational with alkaline batteries, the rechargeable batteries or charger
may need to be replaced.
• The M-175 transmitter must be returned to COMTEK for service if the test
indicator lamp does not illuminate when new alkaline batteries are used.
Transmitter Audio Problem
If...
There is no visual indication on the “voice” modulation level indicator
when speaking into the microphone of the M-175 transmitter...
Then...
• Turn up the microphone gain setting clockwise until the voice
modulation indicator illuminates with speech level.
• Make sure the optional muting switch is in the “mic on” position.
• Check the CM-183RT microphone for a broken or frayed microphone
cord that may cause intermittent operation.
• Test the modulation indicator with the auxiliary audio input using a line
level signal and the CB-36ST auxiliary audio input cable to verify normal
operation. If the auxiliary audio input activates the voice modulation
indicator normally, the CM-183RT microphone may need to be repaired
or replaced.
• The M-175 transmitter must be returned to COMTEK for service if the
auxiliary input test does not activate the voice modulation indicator.
M-175 TROUBLE SHOOTING

Page 14
Possible Causes of Noisy Audio
1. Excessive Distances
Operating at distances greater then 200 ft. may cause some intermittent
noise.
2. Channel Selection
For operation with non-companded receivers (such as PR-75 or PR-72),
the M-175 transmitter must be set to one of 10 non-companded channels
91-00. For high-fidelity operation, the companded channels 1-88 must
be used with companded receiver PR-216/72MHz model.
(See page 9 for Frequency Information.)
3. Gain Problem
Check the microphone gain setting on the M-175 transmitter for normal
operation with the “voice” modulation indicator (See page 2 section d.)
Low modulation will render poor signal-to-noise ratio.
4. Channel Interference
Monitor the receiver with the headphone plugged in and with the
transmitter turned “OFF” on the channel that the transmitter is tuned to.
If interference noise is heard, a new clear channel must be selected.
5. Transmitter Power and Receiver Sensitivity
Check the M-175 transmitter with the PR-75 or PR-216/72MHz receiver
for normal R.F. sensitivity. This can easily be done by range checking the
receiver and transmitter with the microphone cord antenna removed
from the transmitter. Tune the receiver and transmitter to a clear channel
and place the transmitter on a non-metallic table. Remove the microphone
cord antenna from the transmitter, and turn on the transmitter. Plug
the headphone cord into the receiver, and turn the receiver on. Then
walk away from the transmitter while listening for noise build-up
just before the squelch action takes place. A distance of 10 to 15 feet
should be obtained with the PR-75 or PR-72 and 20 to 30 feet with the
PR-216/72MHz receiver. If the receiver and transmitter do not pass this
test, both receiver and transmitter must be returned to COMTEK for service.
M-175 TROUBLE SHOOTING (Continued)

M-175 SPECIFICATIONS
Page 15
Audio Input:
• Microphone input impedance for electret
type microphone - 3000 ohm
• Aux/Line input impedance - 10 k ohm at
0 dBV nominal
Connectors:
Microphone - Micro-mini mono 2.5 mm
Auxiliary - Mini stereo 3.5 mm
Audio: Tip and sleeve
Battery Charging: Tipand sleeve
Controls and Indicators:
• Synthesized channel selection switches
• Power On/Off switch
• Optional microphone switch
• Audio input gain control
• Power/Battery status indicator
• Audio (voice level) modulation indicator
• Manual/Automatic compand switch
Frequency Response:
80 Hz to 10 kHz
Audio Distortion:
Less than 1% at 80% modulation
Modulation Limiter:
Soft compressor with 30 dB linear overload
protection; attack time - less than 1 ms,
recovery time - 10 ms
Frequency Modulation:
10 kHz deviation companded
Operating Radio Frequency:
ity : 88 synthesized channels in the 72-76 MHz
band.
Out-of-Band Emissions:
Better than 50 dB below carrier
R.F. Stability:
20 ppm XTL controlled
Digitally synthesized
RF Power Output:
40 mW to antenna system
FCC Compliance:
Type Accepted under FCC Part 90
Antenna System:
Body-worn microphone cord.
Current Drain:
35 mA average current
Battery:
• 9 volt alkaline Eveready 522
or equivalent for up to 14 hours
of use
• Rechargeable 9 volt Ni-MH
200 mAh battery for up to
7 hours of operation
•
Rechargeable 9 volt Lithium
Polymer 500 mAh battery
for up to 14 hours of use
Dimensions:
1 1 /16" x 2 1 /4" x 3 1 /2 "
(27 mm x 57 mm x 89 mm)
Weight:
5 ounces (140 grams)
NOTE: Specifications subject to
change without notice or
obligation

M-175 WARRANTY AND SERVICE
Warranty
COMTEK transmitters and receivers are warranted to be free from defects in
workmanship and material under normal stand-alone use and conditions for a
period of two years from date of original purchase. Items such as headphones,
earphones, neckloops, and cords are warranted to be free from defects in
workmanship and material for a period of 90 days from the date of original
purchase. Batteries are not covered by this warranty. Damage due to abnormal
use, extreme conditions, misuse, use of the product as a component of another
product, ill treatment and unauthorized modification and repairs are not
covered by this warranty. COMTEK is not liable for any consequential or
punitive damages arising out of any failure of the equipment to perform as
intended. COMTEK shall bear no responsibility or obligation with respect to
the manner of use of any equipment sold by it. COMTEK SPECIFICALLY
DISCLAIMS AND NEGATES ANY WARRANTY OF MERCHANTABILITY
OR FITNESS OF THE PRODUCT FOR A PARTICULAR PURPOSE
INCLUDING, WITHOUT LIMITATION, ANY WARRANTY THAT THE USE
OF SUCH EQUIPMENT FOR ANY PURPOSE WILL COMPLY WITH
APPLICABLE LAWS AND REGULATIONS.
Service Policy
Warranty repairs must be done by COMTEK. Only factory technicians are
authorized to perform warranty service on the M-175 receiver. Before
returning the M-175 for service, a Return Authorization Number should
be obtained from the service department by calling 1-800-496-3463 or
1-801-466-3463. Return the unit to the factory with the original or comparable
packing. COMTEK will pay for insurance and ground return shipping costs in
the United States for all warranty service.
357 West 2700 South • Salt Lake City, Utah 84115 • Phone: [phone] • Fax: [phone] • www.comtek.com
E-mail: [email protected]

357 West 2700 South • Salt Lake City, Utah 84115 • Phone: [phone] • Fax: [phone] • http://www.comtek.com