User Manual Part 1

FSG 90F System
3. Installation
Page 30 November 2000
W. Dittel GmbH
3.5.7 Connection to a 28 Vdc airborne system
Interconnection of the FSG 90F(X) transceivers to a 28 Vdc supply requires a capable
voltage converter. Interconnection wiring shall be according to instructions of the DC
converter's manufacturer. For lighting interconnection refer to Section 3.5.6.
3.6 Post-installation Check
3.6.1 Testing on the Ground with Engine Off
Verification after installation completion
After installing the unit, check all aircraft control movements to be sure no electrical
cable interfere with their operation. All aircraft and radio functions shall be tested after
installation completion to identify, whether malfunctions caused by mechanical and/or
electrical installation work occurs.
This must be performed by an Authorized Aircraft Electronics Inspector.
Testing of antenna matching between the FSG 90F(X) antenna socket (BNC) and the
BNC antenna cable connector is required, using a suitable 50 Ohm VHF Reflectometer
(VSWR meter), or a directional Wattmeter.
The VSWR must be less than 3 : 1 over the full frequency range, tested at least in 1
MHz steps (reflected power shall be less than 25% of the forward RF power output). If
this limit is exceeded, this indicates a mismatched antenna and may be caused by
wrong antenna radiator or counterweight length/dimensions, poor contacts, or damaged
or wrong (no 50 Ohm) coaxial cable.
In order to optimize radio range, it is suggested to care for an VSWR of less than 2 : 1
(reflected power shall be less than 11% of the forward RF power output).
After completion of the antenna matching measurements, perform the following test
sequence:
• All audio level settings (microphone(s), phone(s), speaker, intercom through the
SET-UP (refer to Section 5).
• Check radio with a known base station, as well as with distant airborne station(s).
IMPORTANT!
• If the antenna is belly mounted, perform antenna matching
measurements if possible in flight, or at least while the fuselage is lifted
upwards, using wood/non metallic supporting material. This avoids
antenna mismatch caused from ground proximity.
• Using known, but distant located fixed stations (VOLMET, ATIS) will also
help in determining the radio range, especially in comparison with known,
other radio range results of another aircraft at the same position on the
ground at a known airfield location, or outside of the hangar or workshop.
3.6.2 Ground checks with engine running
It must be ensured that the aircraft's electrical DC system voltage at the FSG 90F(X)
input terminals is within the tolerances permitted at 14 Vdc (or 28 V with DC converter).
Battery only supplied systems operate from 10 to 16.5 Vdc. Such testing requires
normal RPM rated at cruising speed.
This testing evaluates both the audio / noise influence, and RF radio range, at least from
10 to 30 km distance to the ground radio station. With cruising RPM, cabin noise
background content shall almost not exist. Instead, loud and clear communications shall
be achieved!
The microphone shall be in both transmit and intercom mode placed right at the lips in
order to obtain maximum voice level at lowest cabin noise content. Speak loud and