Northern Airborne Technology AA34 User Manual
Page 10
AA34 Series Universal Radio Interface
SM36 Installation and Operation Manual
Section 2 Rev: 1.00
Issue 4
Page 2-4
2.5.1.1
Rear Adjustments
The rear adjustments are potentiometers, accessed through holes in the cover. Rotating a potentiometer
clockwise (cw) will increase the level, and rotating it counterclockwise (ccw) will reduce the level.
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RX LEVEL
Adjusts the signal level of the incoming radio audio.
MIC LEVEL
Adjusts the signal level of the mic output.
S/T LEVEL
Adjusts the signal level of the sidetone.
2.5.1.2
Left side Adjustments
Switches S1 and S2
S1
Provides mic bias to the MIC IN line when closed (default). Open if an external
mic bias is present.
S1 and S2
shown in
OPEN
position
S2
Bypass switch for blocking capacitor in mic out circuit. 'Closed' when bias from
the connected radio will be used for mic excitation. 'Open' (default setting) when
internal bias is used or if there are any concerns about DC interaction between
the AA34 and the connected radio.
RX LEVEL MIC LEVEL S/T LEVEL
Switch C1/C2
This switch determines whether the mic input is amplified. The C1 position provides a direct mic path
from input to output. The C2 (default) position switches in the amplifier.
AA34-200 only
AA34-300 and -301 only
The C1/C2 switch on the AA34-200 units is a rocker
switch with the C1 position to the rear of the access
hole, and the C2 position at the front.
The C1/C2 switch on the AA34-300 and -301 units is a
slide switch with the C1 position to the left of the
access hole and the C2 position to the right.
Switch shown
with C2 Selected
Switch shown with
C2 Selected
Note: If S1 is CLOSED (mic excited by the AA34), and the transformer isolation is NOT used (C1), the
blocking capacitor should be used (S2 OPEN) if the radio’s input circuitry is unknown. This will
prevent any unwanted interaction with DC present at the radio. The DC blocking capacitor is
connected right at the mic output from the AA34, and is used whenever there may be a problem
with DC present at the radio. This capacitor can be used with or without microphone transformer
isolation, which is used to float the microphone from ground.