OPERATION
Voice Transmission
1. Hold the microphone comfortably in the hand positioned so that the Top-Talk Sound Channels� at the top of the case are near the mouth.The clearest sound is often obtained with the microphone at the corner of the mouth, with the cable away from the face. 2. Depress the push-to-talk button and make sure the equipment is in the transmit mode before speaking.
Electrical Characteristics
Operating Voltage
8V
Audio Output Level*
(100 µbar acoustic test signal at 1 kHz, 10 mm) �11.5 dBV (266 mV) �12.8 dBV (230 mV)
12 V
�11.0 dBV (281 mV) �12.0 dBV (250 mV)
28 V
�10.0 dBV (316 mV) �11.2 dBV (275 mV)
Notes
Audio trimpot in factory preset position DTMF trimpot in factory preset position
DTMF Output Level
Dialing
1. Press and hold the push-to-talk button. 2. Press the desired keypad buttons in sequence.A high-pitched tone will confirm that the code has been transmitted. (The microphone audio is muted during DTMF tone transmission.) Operation of microphone and DTMF functions requires that the 888TT be connected to the communications equipment and that the equipment power is turned on. After connection to the communications set, turn the equipment power On. Pressing the push-to-talk switch and observing the keypad LED backlighting can verify power application. Factory preset microphone audio and DTMF levels are correct for aircraft radios with standard input circuits (as defined in RTCA DO-170), and level adjustment should not ordinarily be necessary. When such adjustment is necessary, it should be performed only by Shure Incorporated or by an FAA Approved Service Facility. Use the supplied screwdriver to adjust the microphone sensitivity and DTMF output levels as follows: 1. Microphone sensitivity: Press the push-to-talk button and speak normally into the microphone while checking transmitter modulation.Adjust the microphone sensitivity control (case back, hole �B� in Figure 4) and repeat the talk test as required. 2. DTMF output: Press and hold the push-to-talk button. Depress and hold down a keypad button for a continuous tone. Adjust the DTMF output control (case back, hole �C� in Figure 4) as required.
Dc Supply Current**
6 mA
12 mA
36 mA
*Standard electrical test circuit per RTCA DO-170 **Microphone is powered only while PTT switch is depressed (standby current = 0 if PTT switch is released)
Environmental Conditions Operating Temperature: -40 to 60° C (-40 to 140° F) Storage Temperature: -54 to 85° C (-65 to 185° F) Relative Humidity: 0 to 95% (non-condensing) Microphone Connector 6-conductor modular telephone type PTT Switch Assembly Mechanical: Double-pole, single-throw, leaf-type, normally open Cable ALM-88, detachable MODULINK®, 1.8 m (6 ft) extended cord with modular plug on microphone end and PJ-068 aircraft connector on equipment end; and ALM-89 with A4M type connector. Construction
Case: Black textured high-impact ARMO-DUR®
Switch Button: Black ARMO-DUR® Keypad: Molded silicone rubber Hang-up Loop: Matte finish stainless steel Dimensions See Figure 2 Net Weight (including cable and connector) 283 g (10 oz)
Replacement Parts
Modular plug-cable with PJ-068 plug assembly..ALM-88 A4M type connector ............................................ALM-89
SPECIFICATIONS
Type Electret condenser, noise canceling, with transistor pre-amplifier, DTMF signaling circuitry, illuminated keypad Frequency Response 200 to 4,000 Hz (see Figure 1)
Optional Accessories
Mounting Bracket (3 in kit) .................................. RK6MB
FAA Certification
+10
The Model 888TT is FAA Certified for aircraft use under FAA TSO-C58a requirements. To maintain this FAA Certification, any service required for the Model 888TT must be performed by Shure Incorporated or by an FAA Approved Service Facility.
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0
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TYPICAL FREQUENCY RESPONSE FIGURE ONE Polar Pattern Bidirectional, noise canceling
