FSG 70/FSG 71M
O
PERATION
M
ANUAL
Page
3 - 12
Reprint July 1998
W. Dittel GmbH
3.4.2
Connection of the microphones
Standard carbon microphones and amplifier microphones as well as dynamic
microphones are adaptable to the transceivers without any jumper changing or
soldering work inside the unit. The input for carbon microphones is pin 3, for dynamic
microphones pin 1 of the receptacle. Up to two microphones (pilot and co-pilot) can be
connected. Microphones with less than 30 Ohms must be matched by a transformer.
The shielding of the dynamic microphone cables must be routed separately.
Please refer to Chapter 3.2.1 "Matching of microphones".
IMPORTANT!
Panel jacks of PJ 068 type may only be used in connection with carbon
microphones because of the common ground for microphone and PTT
key. If dynamic microphones without amp are used, a ground loop during
transmit would occur and this results in unstable modulation.
3.4.3
Intercommunication (IC)
The intercom mode is assigned for noisy aircraft. Communication is done via headsets
and requires an on-board wiring according Fig. 3-8/3-9, which includes an IC-switch.
During "ON-Position" the IC-switch disconnects the speaker and activates the
microphone input by connecting pin 5 of receptacle to ground.
Switching ON the IC-switch enables intercom operation and simultaneous listening to
received signals (radio, NAV etc.). Keying the PTT button causes normal TX operation
without having to turn off the IC-switch.
3.4.4
Speaker/Phone connection
Up to two speakers (4 Ohms each) can be connected to the AF-output of the unit
and/or up to three headphones (ca. 300 Ohms each) can be connected to the phone-
output of the unit.
If no speaker is connected, terminating is not necessary.
DANGER!
•
The compass is influenced by the magnetic field of the speaker. A
minimum distance of 1.3 m between our aircraft speaker (Article no
F10061) and the compass should be kept.
3.4.5
AF-External Input
The "AF-Ext. input" (pin 4 of receptacle) is provided to connect the headphone outputs
of other communications equipment. This possibility of interconnecting two or more
units will be used primarily in those aircraft in which only a COM-Transceiver and a
NAV receiver are installed. The headphone output of the NAV unit can then be
connected directly to the AF-Ext. input of the
FSG 70/ FSG 71M
and then be heard
simultaneously from one common headphone or speaker (only during receive mode
possible). To connect more than one external unit isolating resistors (470 Ohms) are
necessary (see Fig. 3-9).
If AF-ext. audio operation is desired, the jumper at P 303 is to be changed as shown in
Fig. 3-10. This inhibits the automatic power saving circuit.
To drive the FSG AF-amplifier to its rated output, an audio input of at least 1 V
eff
is
required (input impedance approx. 10 kOhm). The connections between COM unit and
external units must be shielded.
