FSG 90F System
3. Installation
Page
28
November 2000
W. Dittel GmbH
3.5.2
Microphone Connection
Independent of each other, almost any non-amplified dynamic microphone, or amplified
Electret or amplified dynamic or carbon standard microphones can be connected to the
FSG 90F System
, without internal jumper setting or soldering.
A amplified/carbon microphone is connected to pin 18, a dynamic microphone is
connected to pin 5 of the 25-pole SUB-D receptacle. Avoid any ground loop in
microphone wiring (dynamic non-amplified mike shield shall not be connected to any
other aircraft wiring, except directly at the assigned pin in the accessory connector).
Up to two IDENTICAL microphones for pilot and copilot can be operated in parallel
simultaneously. Even two low impedance (4 Ohm) dynamic microphones may be
connected in parallel as well. However, for microphones with less than 30 Ohms, it may
be necessary to use a suitable microphone transformer.
The associated microphone ground (shield) for dynamic microphones must be
consequently routed galvanically isolated, in order to avoid any ground loop.
This means, dynamic mike ground/shield must be separated from any other grounds for
DC input or DC output, AF input and AF output like speaker, phone, PTT and external
Audio).
In this context, due to the extremely wide mike input level adjustment range, it is
mandatory to understand that correctly matched
FSG 90F(X)
mike input sensitivity (SET-
UP) will be good ONCE FOREVER for this configuration and to ensure stable operation
without audio feedback.
IMPORTANT!
The 3-pole mike connector type PJ-069
MUST NEVER
be used when using
non-amplified dynamic microphones, because ground for mike and PTT is
identical. This would create a ground loop and cause unstable / distorted
modulation. This PJ-068 is allowed only for amplified/carbon mikes.
However, the PJ-068/PJ-55 connector system must be regularly cleaned,
contacts shall have sufficient spring-loaded force. This is especially
mandatory under vibration operating conditions.
3.5.3
Intercom (IC)
Intercom is suitable for twin seater aircraft with noisy cockpit. Intercom as well as radio
operation should employ suitable aircraft headsets which must be matched properly to
the transceiver (refer to SET-UP).
Hand-held microphones may be useful for intercom, if audio is not switched/keyed ON /
OFF by the PTT function. Keying the mike audio may cause awful cracks, depending on
mike technology.
To control the intercom capability, aircraft radio wiring must have a two-pole toggle
switch (refer to figure 3-6 or 3-7). The intercom switch disconnects the loudspeaker
during IC operation in the IC ON position. Simultaneously, pin 7 of the 25-pole connector
is set to ground to select IC ON by continuously activating the microphone amplifier
input signal.
With the IC switch in "ON" position it is possible anytime to perform normal transmitting
(with the normal PTT key), it also allows continuous intercommunication during receive
between pilot and copilot/crew (no PTT action is required for any IC operation).
During receive, while IC is ON, both the IC loudness and external audio volume are
temporarily reduced to improve receive intelligibility.
Receiving volume is set on the
FSG 90F(X)
front panel (VOL), while intercom volume
can be optimized with a SET-UP adjustment.
