Introduction - General Description 1
The ALT 72 is a wideband FM Listening System which
operates in the 72 - 76 MHz frequency band. Designed
for hearing assistance in places of public access, the
ALT 72 is for those who need help overcoming
background noise, reverberation, or distance from the
sound source. It is easily integrated with your existing
sound system.
The Assistive Listening System has two principal parts:
the ALT 72 Assistive Listening Transmitter, and the
MR306 FM Receivers. Audio input to the ALT 72 is
broadcast as an FM signal (72.1 - 72.9 MHz, 74.7 MHz,
and 75.3 - 75.9 MHz) to as many MR306 receivers as
desired. The receivers pick up the broadcast in an area
up to approximately 700,000 square feet (approximate
radius of 500 feet).
ARCHITECTURAL AND ENGINEERING
SPECIFICATIONS
The transmitter shall operate in the 72 - 76 MHz Auditory
Assistance Band as approved by the FCC. Specifically, the
transmitter shall operate on the wideband channels spaced
at 200 kHz increments on frequencies of 72.1 to 72.9 MHz,
74.7 MHz, and 75.3 to 75.9 MHz. The transmitted field
strength shall not exceed 80 millivolts per meter at a 3 meter
distance. The operating frequency shall be programmable
by a front panel 10-position pushwheel switch. The transmit-
ter shall be FCC and Industry Canada approved.
Maximum FM deviation shall not exceed ±75 kHz.
Frequency stability shall be controlled by a phase-locked
loop frequency synthesizer with crystal reference and shall
be accurate within ±0.001% from 0
0
to +50
0
C. The transmit-
ter shall permit fitting of a 7" flexible whip antenna mounted
through the top cover of the unit, or permit connection of an
optional magnet mount antenna, with coaxial cable, to a rear
panel connector. Only the particular antenna type intended
for this connection shall be specified.
The transmitter shall have an XLR connector for balanced
audio input and an RCA Phono connector for unbalanced
audio input. The transmitter shall provide a GROUND LIFT
switch for the XLR input. The transmitter shall permit switch
selection of no limiting, limiting only, or limiting and
compression operation from a front panel switch. There
shall be a front panel control to adjust the audio input level
with an LED MODULATION indicator.
Sound System Amplifier
Microphones (wired or wireless type)
Loudspeakers
Line-Level
Input
Line-Level Output
ALT 72 Transmitter
ALT 72 ASSISTIVE LISTENING TRANSMITTER
INPUT LEVEL
7
+
OFF L C+L
CHANNEL
POWER
MODULATION
LIMITING/
COMPRESSION
1
0
2
3
4
5
6
7
8
9
10
M1
M2
M3
M4
M5
MEMO
TUNING
FM
digital
receiver
®
M1
M2
M3
M4
M5
MEMO
TUNING
FM
digital
receiver
®
MR306 FM Receivers with Earphones
The transmitter shall be powered by an external AC line to
12 VDC power adapter. The rear panel shall have a power
switch and front panel display indication when power is
active. The transmitter shall permit either desktop mounting
or side-by-side mounting in a standard 1 RU rack package.
The receiver shall be tunable in 100 kHz increments for
reception in the 72 - 108.1 MHz Band. Tuning to the
required frequency shall be permitted by the / TUNING
buttons or by user programmable memory recall. The
receiver shall have five preset memory channels that are
recalled by individual memory channel buttons. The receiver
shall be equipped with a LOCK switch to prevent inadvertent
setting changes. The receiver shall be set to either
STEREO or MONO reception with a switch. The receiver
shall have a Volume control. The receiver shall have a 1/8"
stereo/mono headphone connector and a switch to select
audio output to either the headphone (EAR) connector or to
the internal speaker (SPK). The output power shall be 10
mW + 10 mW to the headphone (EAR) connector or 30 mW
to the internal speaker. The receiver shall be powered by
two “AAA” size, 1.5 V batteries with power controlled by an
ON/OFF switch. The headphone wiring shall provide the FM
antenna.
The R.L. Drake ALT 72 Assistive Listening Transmitter with
MR306 FM Receiver(s) system is specified.
