Northern Airborne Technology 270 - Manual (Page 18)

Model 270 Universal Interface Amplifier Manual SM270 Rev. 4.10
Page 2-4 Dec 12, 2006
ENG-FORM: 805-0108.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
AUDIO OUT
(8Ω) LOAD (600Ω)
RELAY
(V/L) FUNCT (K)
SPARE
(L) CTRL (V)
RELAY
(B) BIAS (G)
MIC OUT LOAD -
8
Ω / 600Ω (MS4)
Allows selection of 8
Ω
or 600
Ω
load compatibility for the MIC Output channel.
MIC IN BIAS - G/B
(MS3) Allows selection of 600 Ω ground termination resistance
(G) or DC MIC bias (B) to the
MIC Input channel. Removing MS3 raises the MIC Input channel input impedance to
>10 K
Ω.
2.3.3.3
Jumper Adjustments
Refer to Assembly dwg 270-4100\270-4100 in the SM270 Maintenance manual.
CAUTION
The Model 270 Series Universal Interface Amplifier contains
static sensitive devices. Proper ESD handling procedures must
be followed to prevent damage to the unit.
Access to Jumpers J1 and J2 is by cover removal. To remove the Model 270 cover,
remove the 4 screws in the sides of the unit (do not remove screws under the base of
the unit), and then remove two connector locking-posts that attach the connector to the
cover. Lift the cover to remove. Reinstall the cover by following the same steps in
reverse order. Tighten all screws securely but do not over-tighten.
DC COUPLE (J1)
Allows connection of a series 1
µ
F AC coupling capacitor on the MIC Output channel.
If jumper J1 is installed, the capacitor is shorted providing DC coupling from the
secondary of the transformer on the MIC Output channel
EXT. THLD (J2) Allows connection of an external VOX control potentiometer for the Spare Input
channel. If J2 is installed, the internal VOX threshold potentiometer (VR3) is enabled.
If J2 is removed and VR3 is set to full clockwise position, an external 10 K
Ω
VOX
threshold control potentiometer can be connected.
2.3.4
Mechanical Mounting
The Model 270 can be mounted in any orientation. No shock or vibration isolators are
required.
The case must be grounded to the aircraft structure, either directly or through a
grounding strap of appropriate width according to its length. The case is finished with
electrically insulating and conductive films in accordance with MIL-C-5541.
Note: The finish should not be removed because it prevents corrosion.
W
MIC OUT
X
(8 Ω) LOAD (600Ω)
W
MIC IN
X
(G ) BIAS (Β)