COMTEK BST-25 User Manual

BST-25 / TV 5-6 OPERATOR’S MANUAL (76-88 MHz)

Synthesized
Base Station
Transmitter

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

INTRODUCTION

BST-25 / TV 5-6

Synthesized
Base Station
Transmitter

he BST-25 is a low power auxiliary base station transmitter

T

designed to operate under Part 74 of the FCC Regulations in the
unused TV channel 5 and TV channel 6 spectrum (76.2 to 87.8 MHz).
This transmitter, along with a personal receiver, is used in a TV
production studio for IFB and talent cueing. It may also be used on
remote location from an ENG truck for the same application.

In motion picture production, the BST-25 is used as a low power
auxiliary base station transmitter located on site with the sound
recording equipment. Directors, boom-operators, and others may
receive, with a personal receiver and headphone, the high fidelity
transmission from the BST-25 to monitor sound track audio being
recorded. This transmission, or “Confidence Channel”, may also
be used as an IFB for talent or crew members.

Page 1

OPERATING INSTRUCTIONS

Equipment Placement

If the BST-25 base station is to be rack mounted, a remote
antenna must be used. The base station should be mounted
away from equipment that uses large power transformers to
reduce 60 Hz hum possibilities.

If the base station is to be used outside of a traditional rack­mounted environment, the screw-in whip antenna should be
free of any metallic objects when fully extended.

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 application engineering department for
assistance.

Remote Antenna

When the base station is rack-mounted or when greater system
range is required, a remote antenna should be used. For
vehicle installation, a 1/4 wave roof-mount (MO-1/4 wave
or MAG-1/4 wave) should be used. For field or studio
applications, the COMTEK “Phase Right Antenna”
(PRA-L TV 5-6) is an easy-to-use, high performance, omni
antenna. For high gain directional yagi type antennas and
custom antennas, contact COMTEK’s application engineering
department for assistance.

Please note: Do not install screw-in whip antenna if remote
antenna is used.

Page 2

Power Requirements

The BST-25 base station is designed to be powered by 12 volts
DC. A power adaptor is furnished for use with standard 110V
AC. The on/off switch on the front panel of the base station
turns on the transmitter.

Audio Input Connections

The base station transmitter has facilities for audio input from
a mic, line, or speaker level source. The mic/line level audio
input is a transformer balanced input and requires a standard
XLR-3 male connector. Unbalanced input is accomplished by
shorting pin-3 to pin-1 (audio ground), leaving pin-2 as the
audio source. Please note: when unbalanced input is used, it is

recommended that all audio input cables be kept as short as
possible.

Set-up

a. Select an appropriate location for the base station in

accordance with “Equipment Placement” instructions.

b. Set the “MIC/LINE” switch, located on the back of the
base station transmitter, to the appropriate position: "MIC"
position for low impedance microphones or “LINE” position
for line level feed.

c. Connect the audio source or microphone to the
base station using the appropriate input. Be sure to set the
audio input level adjustment on the base station to its
full counterclockwise position.

Page 3

OPERATING INSTRUCTIONS (continued)

d. Plug the adaptor into a standard AC outlet and plug the
power connector into the DC input jack of the transmitter.
Turn the display switch on the front of the transmitter "ON"
to allow monitoring of the transmitter frequency. Turn the
main power switch on the front of the base station to the "ON"
position. The front display should now be illuminated.

e. Mount the telescoping whip antenna in the hole on
top of the base station rotating it clockwise until it is firmly
seated. Extend the antenna completely. During normal
operation the antenna indicator should not flash. Turn on
the transmitter and verify that the antenna indicator is not
flashing. If the antenna indicator is flashing, shorten the
telescoping whip antenna by 2 inches and again check the
indicator. Continue this procedure until the indicator
remains off. If you experience trouble, please contact
COMTEK's application engineering department for
assistance. If you are using an external type antenna, DO
NOT install the telescoping antenna. Instead, connect the
coaxial feed line for the external antenna to the external
antenna port on the back of the BST-25.

Note:

For optimum performance when using the telescoping
whip antenna, the transmitter should be placed on a large
metallic surface. Adjustment of antenna length for a “No
Flash” condition on antenna indicator will ensure maximum
radiation.

Page 4

Audio Adjustments

In order to ensure the highest possible transmission fidelity,
the transmitter must be modulating at least 50% with normal
speech (-3 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 “MIC/LINE” switch located at the back of the
transmitter should be switched to the appropriate setting:
"MIC" for mic level or weak line level input; “LINE” level for
line level input.

c. The “LEVEL” control on the back of the base station
should be set fully counterclockwise and 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 meter mid-scale. Only very loud
speech or music should deflect the VU meter full-scale.

Frequency Selection

The BST-25 base station transmitter
has the ability to operate on one of 119 preset channels
between 76.200 MHz and 87.800 MHz (TV channel 5 and TV
channel 6). Channels are designated by both frequency and
channel number. Channels which operate in the TV 5
spectrum are prefixed with a 5 (5-50 is 81.100 MHz),
channels operating in the TV 6 spectrum are prefixed with
a 6 (6-50 is 87.100 MHz). This channel rastering makes it easy
to determine which TV band you are operating on.

Page 5

IMPORT ANT