BST -75 OPERATOR’S MANUAL (72-76 MHz)
Synthesized
Base Station
Transmitter
357 West 2700 South • Salt Lake City, Utah 84115 • Phone: (800) 496-3463 • Fax: (801) 484-6906 • www.comtek.com
TABLE OF CONTENTS
Introduction ...........................................................
Equipment Placement ...............................................
Power Requirements .......................................................
Remote Antenna ......................................................
Screw-in Whip Antenna ............................................
Audio Input Connections ...............................................
Audio Adjustments ...............................................
Audio Processing Circuit ..........................................
Front and Rear Panel Facilities ........................................
Frequency Information ..........................................
Accessories ..........................................................
Specifications ......................................................
Warranty and Service ...............................................
1
2
2
3
3
4
4
5
6-7
8-9
10-11
12
13
© 2011 COMTEK® All rights reserved
Printed in U.S.A. 01-18-11
INTRODUCTION
BST-75
Synthesized
Base Station
Transmitter
he BST -75 mini base station transmitter meets the highest
T
professional standards while offering outstanding value
and the most advanced technology available. This versatile and
innovative transmitter is simple to use, yet it has sophisticated
features such as “Flash Memory” 98-channel programmability
with synthesized manual 10-channel selectable user-switch. Plus
a unique multi-function R.F . indicator detects bad antenna load, RF
presence, coaxial cable short or open condition for quick and easy
trouble-shooting.
The compact design of this transmitter is ideal for multiple transmitter
installations. Up to four transmitters can be installed in one rack
space. Also, it operates in the 72-76 MHz band under FCC Regulation
Part 90. This allows a greater RF power capability (120 mW) for greater
range and reliability than customary FCC Part 15 systems.
The audio processing circuit produces full fidelity frequency response
from 80 Hz to 10 kHz with very low residual F.M. noise and distortion.
T o accommodate a greater variety of receivers, the BST -75 can operate
with non-companded receivers or with companded receivers for higher
fidelity sound reproduction with a signal-to-noise ratio of up to 100 dB.
All this is designed into a stylish, compact, all-metal enclosure suitable
for permanent rack-mount installations or can be battery powered for
stand-alone portable applications.
Page 1
OPERATING INSTRUCTIONS
Equipment Placement
If the BST-75 base station is to be rack mounted, a r emote antenna must
be used. The base station should be mounted away from equipment
that uses large power transformers to reduce 60 Hz hum possibilities.
Special Note: When using the base station in close proximity to other
audio equipment, ensure that the audio equipment is not susceptible to
RF interference. This can be accomplished by temporarily installing
the base station as per above, and then while the base station is
operating, checking all audio outputs for uncharacteristic noise. If a
problem is found, move the base station or the remote antenna as far as
possible from the affected equipment. Should you continue to have
problems, contact COMTEK’s Technical Support Services for
ass istance.
Power Requirements
The BST-75 base station is designed to be power ed by 12 volts AC
through a standard barrel type power jack (5.5mm X 2.1mm). The
AC power adaptor supplied (AP-12V AC) is used for permanent
installations and mobile applications
where AC power is available.
For field operation only , the
BST-75 base station will accept
12V DC through the power jack
with either positive or negative
12V to the center pin of the jack.
The on/off switch on the front
panel of the base station
transmitter should be
turned to the “off”
position when the power
plug is initially plugged
into the transmitter .
Page 2
OPERATING INSTRUCTIONS
Remote Antenna
When the BST-75 base station transmitter
is to be rack mounted for permanent
installation, a remote antenna must
be used. The RDA-2B remote dipole
antenna (or equivalent) or the COMTEK
“Phase Right Antenna” PRA-L72 high
performance omni antenna should be
used. These antennas must be placed
vertically polarized up to twenty feet
away from the transmitter with the
coaxial cable supplied. The highest
possible antenna placement away from
any metallic object is best. For high gain
directional yagi type antennas and
specialty antennas, contact COMTEK’s
Technical Support Services.
Integral Screw-in Whip Antenna
If the BST-75 base station transmitter is to be
used outside of the traditional rack-mounted
environment for stand-alone mobile type
applications, the screw-in whip antenna
(TWA-75) should be used. The transmitter
should be placed on a table or platform as
high as possible so the fully extended
whip antenna is at least 24” away from
any metallic object. The radiated output
power of the transmitter with this whip
antenna will not be as great as the remote
antennas. The BST-75 transmitter should
only be used in the high power setting when
the telescoping whip antenna is used.
Page 3
OPERATING INSTRUCTIONS
Audio Input Connections
The BST 75-216 base station transmitter uses an XLR-3F connector with
a “Combo” phone jack. The XLR portion of the connector will accept
a true balanced or unbalanced line level signal up to +20 dBm. The
1/4” mono jack portion of the connector can be used for AUX level
audio or line level audio up to +5 dBm. It also can be used to directly
phantom-power most two-conductor electret headset microphones.
Note: For best performance,
the 1/4” mono jack should be
considered the primary choice
for shorter audio line feed.
Audio Adjustments
In order to ensure the highest possible transmission fidelity, the
transmitter must be modulating at least 50% with normal speech
(0 dB on the VU meter). This adjustment is made in the following
manner:
a. Ensure that the audio source has been optimized for best
signal-to-noise ratio.
b. The XLR-3 connector located on the back of the transmitter is
used for line level balanced or unbalanced audio source (up to +20 dBm).
c. Set the AF Gain Control on the back of the base station to fully
counterclockwise. Then, while normal program information is present,
slowly rotate the “LEVEL” control clockwise until the VU meter on the
front panel begins to deflect. Adjustment should be made so that
normal speech or music deflects the 0 dB yellow LED. Only peak level
of speech or music should deflect the VU meter full-scale into the last
red LED.
Page 4
OPERATING INSTRUCTIONS
Audio Processing Circuit
The audio processing system incorporates a peak-level compressor to
prevent over-modulation and reduce audio distortion at high levels.
This compressor has a very fast attack time and a carefully controlled
decay time to optimize the dynamic performance of the audio processing system. (The VU meter will indicate this compressor action when
the red LEDs are illuminated.) The audio is also equalized to add
pre-emphasis as well as a very sharp high frequency roll-off circuit to
minimize high frequency noise in the audio signal. The total frequency
response and performance of the system is, however , determined by the
corresponding de-emphasis and equalization used in the receiver .
In order to accommodate a greater variety of receivers, the BST -75
transmitter incorporates the option to operate with receivers that have
companded or non-companded audio pr ocessing. However , the BST-75
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.
Page 5
BST-75 FRONT PANEL
1
2 6
3 54
1
OPTIONAL ANTENNA: Used for mobile type applications.
POWER SWITCH: Turns the transmitter on or off.
2
3
POWER LED INDICATOR: Illuminates when the power is on.
VU METER: Displays the audio level being used for modulation.
4
(See Audio Adjustment Section.)
ANTENNA INDICATOR: Flashes when transmitter detects coaxial
5
cable shorts and open conditions, bad antenna load.
RACK-MOUNTING SCREWS: Used for mounting BST-75 to
6
rack-mounting panels.
Page 6
BST-75 REAR PANEL
7 109 128
POWER INPUT JACK: Requires 12V AC at 200 mA. Will also accept 12V
7
DC with either positive or negative center pin (for field operation only).
8
CHANNEL SELECTOR SWITCH: Selects the frequency on which the
transmitter will operate. (See Frequency Information Section.)
9
EXTERNAL ANTENNA JACK: BNC connector provides a standard
50 ohm RF output for use with an external antenna.
10
RF POWER SWITCH: Adjusts the RF power output of the transmitter
(High-120mW, Mid-40mW, Low-10mW).
AUDIO LEVEL CONTR OL: This control is used to set the proper
11
modulation level when referenced with the VU meter.
12
MIC / LINE AUDIO INPUT : XLR-3 accepts balanced line level input.
1/4” phone jack accepts 2-conductor electret microphone type only.
11
Page 7
BST-75 FREQUENCY INFORMATION
USER-SWITCHABLE
ST ANDARD CHANNELS
NON-COMPANDED
CHANNEL
A #1
B #2
C #3
D #4
E #5
F #6
G #7
H #8
I #9
J #10
FREQUENCY
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
GROUP FREQUENCY CHART
GROUP 1
CHANNEL
A #1
E #5
H #8
J #10
FREQUENCY
72.1 MHz
72.9 MHz
75.9 MHz
75.3 MHz
GROUP FREQUENCY CHART
GROUP 2
CHANNEL
B #2
G #7
I #9
FREQUENCY
72.3 MHz
75.7 MHz
74.7 MHz
GROUP FREQUENCY CHART
GROUP 3
CHANNEL
C #3
F #6
FREQUENCY
72.5 MHz
75.5 MHz
AV AILABLE 72-76 MHz
“FLASH MEMORY”
COMP ANDED CHANNELS
CHAN FREQ
72.02 MHz
01
72.04 MHz
02
72.06 MHz
03
72.08 MHz
04
72.10 MHz
05
72.12 MHz
06
72.14 MHz
07
72.16 MHz
08
72.18 MHz
09
72.20 MHz
10
72.22 MHz
11
72.24 MHz
12
72.26 MHz
13
72.28 MHz
14
72.30 MHz
15
72.32 MHz
16
72.34 MHz
17
72.36 MHz
18
72.38 MHz
19
72.40 MHz
20
72.42 MHz
21
72.46 MHz
22
72.50 MHz
23
72.54 MHz
24
72.58 MHz
25
72.62 MHz
26
72.64 MHz
27
72.66 MHz
28
72.68 MHz
29
72.70 MHz
30
72.72 MHz
31
72.74 MHz
32
72.76 MHz
33
72.78 MHz
34
CHAN FREQ
72.80 MHz
35
72.82 MHz
36
72.84 MHz
37
72.86 MHz
38
72.88 MHz
39
72.90 MHz
40
72.92 MHz
41
72.94 MHz
42
72.96 MHz
43
72.98 MHz
44
74.61 MHz
45
74.63 MHz
46
74.65 MHz
47
74.67 MHz
48
74.69 MHz
49
74.71 MHz
50
74.73 MHz
51
74.75 MHz
52
74.77 MHz
53
74.79 MHz
54
75.21 MHz
55
75.23 MHz
56
75.25 MHz
57
75.27 MHz
58
75.29 MHz
59
75.31 MHz
60
75.33 MHz
61
75.35 MHz
62
75.37 MHz
63
75.39 MHz
64
75.42MHz
65
75.46 MHz
66
75.50 MHz
67
75.54 MHz
68
GROUP FREQUENCY CHARTS
GROUP 1
CHAN FREQ
72.02 MHz
01
72.22 MHz
11
72.72 MHz
31
74.61 MHz
45
75.62 MHz
70
75.72 MHz
75
GROUP 2
CHAN FREQ
72.08 MHz
04
72.18 MHz
09
72.72 MHz
31
74.77 MHz
53
75.58 MHz
69
75.92 MHz
85
CHAN FREQ
75.58 MHz
69
75.62 MHz
70
75.64 MHz
71
75.66 MHz
72
75.68 MHz
73
75.70 MHz
74
75.72 MHz
75
75.74 MHz
76
75.76 MHz
77
75.78 MHz
78
75.80 MHz
79
75.82 MHz
80
75.84 MHz
81
75.86 MHz
82
75.88 MHz
83
75.90 MHz
84
75.92 MHz
85
75.94 MHz
86
75.96 MHz
87
75.98 MHz
88
GROUP 3
CHAN FREQ
13
72.26 MHz
25
72.58 MHz
54
74.79 MHz
57
75.25 MHz
81
75.84 MHz
87
75.96 MHz
Page 8
BST-75 FREQUENCY INFORMATION
Frequency Selection
The BST-75 transmitter comes fr om the factory on 10 standard
manually selectable channels. Other group frequencies are available
from the 88 “Flash Memory” programmable channel list and have been
coordinated for simultaneous operation. These group frequencies
can be programmed for use with the manual 10-channel selectable
user-switch. Frequency coordination and after-sale programming for
different compatible frequency groups can be done through COMTEK’s
T echnical Support Services. Fr equency selection software may be
downloaded from COMTEK’s website at www .comtek/software.html
Multiple Channel Operation
When multiple transmitters (more than two) are used in the same
proximity , intermodulation interfer ence can occur . This condition
is common to all radio receivers to some extent when multiple
transmitters are used in the same operating area. The RF signals will
“MIX” together generating additional signals. If these product
frequencies are too close to a frequency which the receiver can also
respond to, you will experience intermodulation interference which
may cause undesirable operation.
T o avoid this type of interference when multiple transmitters ar e
used in the same proximity, transmitting frequencies must
be coordinated by selecting from frequencies in
the same group.
Group 1
operating area
(See group frequency chart on page 6.)
T ransmitter 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.
Page 9
Group 2
operating area
transmitters
Transmitter
separation
operating area
Group 3
transmitterstransmitters
Transmitter
separation
BST-75 ACCESSORIES
Included Accessories
1. C-75 Carrying case
2. BST-75 Operator’s manual
3. TW A-75 Telescoping
whip antenna
4. AP-12VAC Power adaptor
(115V AC Input)
5. BST-75 Base station transmitter
Page 10
BST-75 ACCESSORIES
Optional Accessories
1. RDA-2B Remote
dipole antenna
2. PRA Phase-Right
coaxial antenna
3. PRA Phase-Right
antenna mount
4. HM-100 1/4” Behind-the-neck
directional boom microphone
5. RMK 75-4 Quad
rack-mount face plate
6. RMK 75-2 Double
rack-mount face plate
7. RMK 75 Single
rack-mount face plate
Page 11
BST-75 SPECIFICATIONS
Audio Inputs:
•
Line level balanced input
0 dBm for 80% modulation
(+20 dBm max, XLR-3F)
•
Unbalanced input (+5 d B m Max)
or two wire electret microphone
with bias voltage for electret
microphone (-35 dBv at 5 K ohms)
with 1/4” phone jack.
Connectors:
XLR-3F Combo with 1/4”
•
phone jack
Barrel type 5.5mm X 2.1mm
•
power jack AC or DC
BNC type RF output
•
Operation Indicators:
•
LED bargraph VU meter
•
LED antenna load and coaxial
cable condition indicator
•
LED DC power indicator
Antenna:
19” Telescopic antenna mounts
•
directly into top of transmitter
BNC RF output connector for
•
optional external antenna
FCC Compliance:
Type Accepted under FCC
Part 90
Power Requirements:
12 Volts AC or DC, 200 mA max
Frequency Response:
80 Hz to 10 kHz
Audio Distortion:
Less than 0.5% at 80% modulation
Modulation Limiter:
Peak compressor type with
high linear overload protection
(25 dB). Attack time less than
1 ms, recovery time 10 ms
Audio Processing:
Companded and non-companded
to accommodate a variety of
receivers
Audio Gain Control:
Limited to 20 dB
Frequency Modulation:
10 kHz deviation for
narrow band companded
RF Output Power:
Maximum power output for
FCC Part 90 (120mW)
Frequency Stability:
Better than 0.002% digitally
synthesized, crystal controlled
Operating Frequency:
72.020 to 75.980 MHz
88 “Flash Memory”
programmable channels
Harmonic and Spurious Emissions:
Better than 50 dB below carrier
Dimensions:
3
3/4"
X 1
5/8"
X 5
1/4" deep
Weight:
15
1/4 oz.
Page 12
NOTE: Specifications subject to
change without notice
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
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 W ARR AN T Y O F 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.
two years from date of original purchase. Items such as headphones,
Service Policy
Warranty repairs must be done by COMTEK. Only factory technicians are
authorized to perform warranty service on the BST-75 transmitter. Before
returning the BST-75 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: (800) 496-3463 • Fax: (801) 484-6906 • www.comtek.com
E-mail: sales@comtek.com
357 West 2700 South • Salt Lake City, Utah 84115 • Phone: (800) 496-3463 • Fax: (801) 484-6906 • www.comtek.com
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