FSG 90 System
3 Installation
December 2014 FAV_D10024 29
3.6.5 AF External Operation
The AF external input pin 4 may be connected to any external (selectable) audio output
of any other audio source. 1 Volt rms is necessary to obtain maximum audio volume.
Higher AF input may cause audio distortion. External AF will be audible only in Receive
mode and in Standby mode, and may be heard in both speaker and headphones. During
transmit, the external AF input is disabled.
Continuous interconnection of an external audio source(s) will be suitable especially in
aircraft using just one COM and one NAV. The NAV headphone output may then be
connected directly to the FSG 90(X) external AF input.
This allows in addition to the receiving and intercom function also the simultaneous
listening of COM and NAV audio either by headphones or by speaker.
Interconnection of more than one external audio source requires additional external
decoupling/isolation resistors (470 Ohms, refer to figure 3-7).
The individual audio volume is set directly at the particular external equipment.
IMPORTANT!
If external audio sources should be audible via A/C speaker, the external
AF input must be enabled in the SET-UP. The 30 mA current saving in
Standby Mode is then disabled.
To achieve in External Audio operation the maximum FSG 90(X) audio output power, a
minimum AF input level of 1 Volt rms is required (approx. 10 kOhm input impedance).
Interconnecting AF wiring must use shielded wires in order to avoid interference from
strong electrical fields. An eventually magnetic interference coupling shall be especially
regarded (distance from high current carrying wiring).
3.6.6 Lighting the Frequency Display
IMPORTANT!
Lighting is turned on or off via a separate input, but can be controlled by
the radio, if desired.
In order to save current while supplied from battery an external suitable
illumination switch is suggested.
The FSG 90(X) includes an LC display which can be back-lit. Pin 23 may be connected
either directly to the 13.8 Vdc A/C power (perhaps via a suitable dimmer), or to the
switched DC output Pin 24. For display lighting from a 28 Vdc A/C supply, insert a 680
Ohm resistor / 0.5 W, connected in series.
CAUTION!
This way of matching to 28 Volt is only suitable for the lighting!
The FSG 90(X) always requires a 12 to 14 Volts DC supply.
3.6.7 Connection to a 28 Vdc airborne system
Interconnection of the FSG 90(X) transceivers to a 28 Vdc supply requires a capable
voltage converter. Interconnection wiring shall be according to instructions of the DC
converter manufacturer. For lighting interconnection, refer to Section 3.5.6.
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