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The 885TT is designed for use with most currently available mobile
two-way radio transceivers. For installation convenience, all microphone
and signalling functions, including keypad illumination, are powered directly
from the microphone input circuit of most transmitters, minimizing the
need for equipment modification.The microphone is compatible with a
choice of five-conductor, pre-wired, coil-cord MODULINK
®
cables (sold
separately), each of which has a telephone-type modular plug on the
microphone end, and a choice of popular transmitter input connectors
on the other. One cable model is supplied without a connector on the
transceiver end so that the user or installer can attach the desired
connector.The cables are instantly changed or replaced without soldering.
The 885TT features attractive, contemporary styling, designed to
blend with most radio designs and vehicle interiors.The microphone is
ergonomically designed; it fits naturally and comfortably in the hand and
is not affected by heat or humidity.The rugged ARMO-DUR
®
case is
immune to oil, grease, most fumes and solvents, salt spray, sun, rust and
corrosion. It is outstanding in its ability to withstand mechanical shocks
and vibration.The Million-Cycle Plus
™
leaf-type switch is a double-pole,
single-throw type, de-signed to resist the effects of severe operating
conditions and constant usage. It has nickel-silver blades, and its contacts
are palladium-alloyed for reliable, oxidation-free operation.
The 885TT’s keypad is made of tough silicone rubber, with durable
printed characters that will last the life of the microphone.The
keypad is backlit by red LEDs, easily visible during night operation
and minimizing eye readjustment for night vision.
The 885TT is supplied with a small screwdriver for adjusting the
microphone amplifier gain and DTMF level, and for releasing the
modular-plug microphone cable from the microphone. Mounting
brackets for affixing to radio equipment or other surfaces are available
in quantities of three as Shure RK6MB.
GENERAL DESCRIPTION
CONTINUED
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(Test conditions unless otherwise specified:
audio output measured between pin 2 and
ground; PTT switch depressed; no hang-up
button connection; mic and DTMF level
trimmers full clockwise; dc DMM 10 M or
greater input impedance; ac DMM 1 M or
greater input impedance.Test circuit as
shown in Figure 3B.)
Type
Electret condenser (with transistor
preamplifier, DTMF signaling circuitry,
illuminated keypad)
Frequency Response
200 to 5,000 Hz (see Figure 1)
Polar Pattern
Omnidirectional
Output Level
(at 1,000 Hz, 1 cm)
-26 dB/Pa (0 dB = 1 V/Pascal)
DC Supply Current
2.3 mA
Magnetic Hum Sensitivity
-94 dBV maximum in 1 Oe 60 Hz field
(mic level control full counterclockwise)
DTMF Output Level
1.1 V peak-to-peak
Audio Polarity
Positive sound pressure produces positive
voltage at pins 2 and 6 of modular connector
with respect to ground
Microphone Connector
6-conductor modular telephone type
Environmental Conditions
Operating Temperature: -30° to 60° C
(-22° to 140° F)
Storage Temperature: -40° to 74° C
(-40° to 165° F)
Relative Humidity: 0 to 95%
(non-condensing)
PTT Switch Assembly
Mechanical: Double pole, single-throw,
leaf-type, normally open Electronic: Open
NPN transistor collector to ground; positive
polarity only; maximum on-state current
100 mA to produce 0.8 V or less; maximum
off-state voltage 40 V.
Cable
(optional choice)
Detachable, 1.8m (6 ft.), 5-conductor
(1 shielded), vinyl-rubber-jacketed coil cord
with modular plug on microphone end
(see Cordset Table for available installed
equipment plugs)
Construction
Case: Black textured high-impact ARMO-DUR
®
Switch Button: Black ARMO-DUR
®
Keypad: Molded silicone rubber
Dimensions
See Figure 2
SPECIFICATIONS
The 885TT is provided with a rear-case hang-up button for use with a mounting bracket on or near associated equipment. Heavy-duty,
chrome-plated mounting brackets are available in quantities of three as Shure Part No. RK6MB. IMPORTANT:The microphone hang-up button
is connected to the blue cable conductor for radios with microphone hang-up sensing and must be grounded for proper operation.
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SET-UP
CONNECTIONS
The 885TT is designed to operate with two-way radio sets with input circuits similar to those in Figure 3.When wiring ALM-1 cables with
connectors for radios not listed in the table, modular connector pin 2 is to be used for the dc bias resistor on the input (see Modifications section).
Adjustments
After connection to the communications equipment and with equipment power turned on, the microphone sensitivity and DTMF output levels
should be adjusted with the supplied screwdriver as follows.
1.
MICROPHONE SENSITIVITY: Press the push-to-talk button and speak normally
into the microphone while observing transmitter modulation. Adjust the microphone sensitivity control (rear case hole “B” in Figure 5) and
repeat the talk test as required.
2.
DTMF OUTPUT: Do not press the push-to-talk button. Depress and hold down a keypad button for a
continuous tone. Adjust the DTMF output control (rear case hole “C” in Figure 5) as required.
Microphone Cables
The 885TT can be used with various MODULINK
®
microphone cables. Each cable has a modular microphone plug on one end and the
user’s choice of equipment plugs on the other.The MODULINK
®
Cordset Table supplied with the 885TT lists the most popular radios available
and the cordset (ALM-) designed for use with each. Note that the ALM-1 has no connector on the equipment end; it can be wired as needed.
The cable is attached to the 885TT by inserting the modular telephone-type plug in the microphone jack until it locks.To remove the cable
from the microphone, insert the small screwdriver supplied with the 885TT in rear case hole “A” just above the cable jack (see Figure 5) to
unlock the plug and withdraw the plug from the jack.
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