Northern Airborne Technology 270 - Manual (Page 11)

SM270 Rev. 4.10 Model 270 Universal Interface Amplifier Manual
Spare Output
Channel The Spare Output channel is fed by the Spare Input channel. A
Voice Activated Switch circuit (VOX) is installed in the amplifier
circuit between the Spare Input and Spare Output channels.
The VOX circuit activation threshold is adjustable over a range
of 20 mVrms to 250 mVrms by trim potentiometer VR3. Refer
also to the External VOX threshold adjustment description. The
Spare Output channel is suited to driving loads in the range
from 150
Ω to greater than 600 Ω and the Spare Output
channel can drive DC-biased or ground-referenced loads.
External VOX
THLD The Spare audio channel Voice Activated Switch can be
controlled by an externally connected 10 K
Ω linear potentiometer.
To connect the potentiometer, remove internal jumper J2 and
set trim potentiometer VR3 to full clockwise position (10 turns),
then connect the external 10 K
Ω potentiometer from the
External VOX THLD input pin to ground. Maximum VOX
threshold is achieved when the external VOX THLD pot is set
for 0
Ω.
Switching Relay The Switching Relay is for general-purpose audio or control
switching functions. The relay contacts are rated for 28 Vdc @
2 Amps, AC or DC non-inductive loads. If inductive loads are
connected, a snubber diode should be installed across the load
inductor coil to prevent high re-coil voltages (e.g. 'back-EMF')
from entering the relay contacts. The switching relay has 3
modes of operation explained below.
KEYED Input
(PTT relay control) The Keyed Input is designed to control the internal switching
relay. If mini-switch MS6 is set to the Keyed position, the Keyed
Input will activate the relay when a ground signal is applied to
the input. Ground current for the keyed input is < 100 mA.
KEYED Input
(Alternate Action
relay control) The Keyed Input can also control an alternate action flip-flop
circuit. If mini-switch MS6 is set to the VOX/LATCH position and
MS1 is set to the LATCH position, alternate action relay function
is selected. Each time a ground is applied to the Keyed Input,
the relay will toggle to the next position.
VOX relay control If mini-switch MS6 is set to the VOX/LATCH position and MS1
is set to the VOX position, control of the switching relay is
connected to the Spare Audio input channel VOX circuit. With
VOX control, each time an audio signal at the Spare Input
crosses the VOX threshold, the relay is activated for the
duration of time that the VOX threshold is exceeded. When the
audio level to the Spare Input channel drops below the VOX
threshold, the relay will disengage after an approximate
2-second delay.
Dec 12, 2006 Page 1-3
ENG-FORM: 800-0108.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.