Northern Airborne Technology MI34 - Manual (Page 25)

SM29 Rev. 4.00 MI34 Mobile Interface Manual
Nov 20, 2003 Page 3-1
ENG-FORM: 806-0104.DOT
PROPRIETARY AND CONFIDENTIAL TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Section 3.0 Operation
3.1
General
The operation of the MI34 is generally as part of a NAT system including a Tac/Com
control head and NAT MT series (Midland Syn-Tech I) or NAT MT/XTR series (Midland
Syn-Tech XTR) radio.
The MI34 provides a method of coupling the radios into the aircraft audio system. It can
provide the excitation needed for standard aircraft microphones and can output the mic
signal through a floating transformer winding to eliminate any ground loop or polarity
problems. The microphone signal is also used to generate adjustable artificial sidetone
which is echoed back to the audio system on the receive line. Receive Audio interface
is provided with level adjustments and floating connections.
In normal use the operation is completely transparent to the user.
3.2
Configuration
The units are normally shipped from NAT with the C1/C2 switch in the C1 position. This
bypasses the mic coupling transformer output and the mic is wired direct through the
MI34. The S1 switch is set in the 'ON' position providing internal mic bias, and the S2
switch is set to 'OFF' allowing C114 (DC blocking capacitor) to be in series in the MIC HI
audio line. With the C1/C2 switch in the C1 position, the Microphone (mic) adjustment
(R109) is taken out of the circuit and has no effect.
The Receive Audio (RX) level (R112) is set to 200 mW into 600
Ω with a standard RX
signal of 2.5 Vrms.
The Sidetone (S/T) level (R104) is set to 25 mW into 600
Ω with a standard mic signal
of 250 mVrms.
End of section 3.0