COMTEK BST 25-216 User Manual

BST 25-216 OPERATOR’S MANUAL (216 MHz)

Synthesized
Base Station
Transmitter

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

INTRODUCTION

BST 25-216

Synthesized
Base Station
Transmitter

he BST 25-216 is a professional quality, auxiliary base station

T

transmitter designed to operate with the PR-216 and PR-216
Option 7 synthesized receivers in the 216-217 MHz band, and is
granted under FCC Parts 22, 74, and 90. This transmitter may
be used for personal cueing, for tour guide applications,
language interpretation, and for assistive listening. For
highest fidelity operation, the PR-216 receiver must be
used with the wide-band companded channels.

The BST 25-216 also operates with the Phonak microEar VHF
in-ear receiver in the narrow-band non-companded channels.

The BST 25-216 transmitter incorporates the latest digital and
analog technologies to produce low residual noise, wide
dynamic range, and extended frequency response rendering the
most natural sound possible from a wireless system.

Page 1

OPERATING INSTRUCTIONS

Equipment Placement

If the BST 25-216 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
(12 1/2 inches).

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-H 216 MHz) 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 25-216 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 (12 1/2 inches).
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, it is an indication that the antenna is not fully
efficient. The antenna should be checked for appropriate
length, antenna elements in too close proximity to metallic
objects, or for a damaged coaxial cable to remote
antenna. Also, DO NOT install screw-in whip antenna if
remote antenna is used.

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:

Page 4

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

IMPORTANT

The BST 25-216 MHz base station transmitter can operate on
60 channels between 216 MHz and 217 MHz. Channels 1-40
are narrow-band channels for use with the Phonak microEar
receiver with 5 KHz deviation. Channels 41-60 are wide­band channels for use with COMTEK PR-216 receiver with
10 KHz deviation. The PR-216 will tune the Phonak
microEar channels 1-40 but with lesser fidelity. Refer to
page 10 for Channel/Frequency Chart.

Multiple Channel Operation

Simultaneous operation of more than two channels requires
coordination of the frequencies that are used to avoid
intermodulation interference.

Page 5