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H E A D S
U P
T E C H N O L
If the system is configured as a receiver-only, without a XMC control head, the
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"power enable" input (J1-18) must be strapped to 28VDC DC power.
The receiver provides stereo (left and right) 600 transformer balanced audio
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outputs for each receiver module. It is recommended that each audio source is
amplified for the best audio quality. If headphones are connected directly to the
receiver audio output, the audio level may not be sufficient.
3.4 Antenna Installation Considerations
The XMR System is designed for use with various XM Radio type-certified antennas
covering the S-Band from 2.332 GHz to 2.345 GHz. Due to the low signal levels inherent
with satellite communications, the following guidelines and recommended practices
should be adhered to for the design of the antenna installation:
Install IAW AC 43.13-2A Chapter 3, AC 43.13-1B Chapter 11, antenna
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manufacturer instructions, and in a manner acceptable to the administrator.
Mount the antenna on the top of the aircraft to an external surface such as the
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fuselage, away from vertical obstructions as to not "shadow" the antenna from
line-of-sight reception of the satellites. (Mount antenna as high on the fuselage
as practical). Relocation of other less location-sensitive transmitters may be
necessary to achieve optimal XM reception performance.
The mounting of the antenna must provide an electrical bond of 0.003 Ohms or
•
less the airframe ground.
3.4.1
Antenna Coaxial Cable Installation
The correct cable loss of the antenna feed cable is critical to the performance of the
system operation. The design configuration of the receiver's input is preset to expect a
total gain range of 22dB (+/- 2dB).
Typical XM Radio type-certified aircraft antennas are configured with a total gain of 30-
34dB where 10dB of total cable loss provides the correct gain to the receiver. Always
refer to the antenna specifications to insure the correct gain. If desired, additional loss of
0.3dB for each SMA connector can be added but is not crucial to system performance.
Table 1 below provides reference information for lengths for various 50-ohm cable types
that are commonly used with SMA connectors to produce the acceptable loss when
used with antennas with 30-34dB of gain. When antennas of other gain values are
installed, the cable length can be determined using the second column of Table 1 below
as follows:
Cable Length (Ft.) = (Antenna Gain – 22) / Loss Rating X 100
When the distance between the antenna and receiver is short, run the amount of cable
required to meet the loss requirement and stow excess length. An alternative to stowing
large amounts of excess cable is to install a low power RF attenuator in-line with the
cable. This system requires a DC bias passing type attenuator that has a frequency
rating that falls within the maximum satellite frequency of 2.345 GHz.
XMR-3
Rev. C, 04/05/06
O G I E S
XM Radio
Installation Manual
Page 15 of 31
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