Northern Airborne Technology 270 - Manual (Page 10)

Model 270 Universal Interface Amplifier Manual SM270 Rev. 4.10
1.4 Specifications
1.4.1 Electrical Specifications
1.4.1.1 Functions
FUNCTION DESCRIPTION
Audio Input Channel
(receiver audio)
A 600 Ω balanced audio input that is routed to the Audio Output
channel.
MIC Input Channel A single-ended input (ground referenced) that is routed to the
MIC Output channel and to the Audio Output channel if desired
for MIC Sidetone. A 22 mAdc microphone bias from a 9 Vdc
@
400 Ω source or a 600 Ω ground termination resistance are
selectable by mini-switch MS3. MS3 can also be unplugged to
raise the input impedance to >10 K
Ω.
This input is suitable for microphone input signals or any other
low level audio signals in a range from 20 mVrms to 1.5 Vrms.
Spare Input
Channel A single-ended input (ground referenced) that is routed to the
Spare Output channel. A 22 mAdc microphone bias from a 9
Vdc
@ 400 Ω source or a 600 Ω ground termination resistance
are selectable by mini-switch MS2. MS2 can also be unplugged
to raise the input impedance to >10 K
Ω.
This input is suitable for microphone input signals or any other
low level audio signals in a range from 20 mVrms to 1.5 Vrms.
Audio Output
Channel
(receiver or
headphone audio) The Audio Output channel is fed by the Audio Input channel.
The amplifier gain for the Audio Output channel is adjustable by
trim potentiometer VR2. MIC Sidetone audio from the MIC
Input channel can also be routed to the Audio Output channel if
VR2 is adjusted for the desired level. Set VR4 fully counter-
clockwise if MIC Sidetone is not desired.
The Audio Output channel can drive loads ranging from 8
Ω to
greater than 600 Ω. Mini-switch MS5 is used to select 8 Ω or 600 Ω
load compatibility. The Audio Output channel is transformer
coupled.
MIC Output
Channel The MIC Output channel is fed by the MIC Input channel. The
amplifier gain for the MIC Output channel is adjustable by trim
potentiometer VR1. The MIC Output channel can drive loads
ranging from 8
Ω to greater than 600 Ω. Mini-switch MS4 is
used to select 8 Ω or 600 Ω load compatibility. The MIC Output
channel is transformer coupled and also includes a 1 µF AC
coupling capacitor. Internal jumperJ1 is installed if direct DC
coupling from the transformer secondary is desired. Remove
J1 if AC coupling is desired. The MIC Output can drive DC-
biased or ground-referenced loads if AC coupled.
Page 1-2 Dec 12, 2006
ENG-FORM: 800-0108.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.