Table 2-7. Xm Gain/Loss Component Calculation - Garmin GDL 69/69A Installation Manual

Xm satellite radio data link receiver

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Activation instructions (36 pages)

Table Of Contents

Table of Contents

Note:

(1)

Garmin GA 55, GA 55A, GA 57 XM antenna typical gain 25 dB. For antenna gain for other

antennas, see manufacturer's specifications.

(2)

If 12-16ft of RG-400/U cable is used, a value of 4.5dB can be used. See Section 2.6.4.1 for

explanation of calculation.

(3)

If an antenna with increased gain is installed (antenna other than the Garmin antennas listed in

Table 1-5), additional cable length may be required to be coiled to compensate for the required

cable loss. Alternately, an external attenuator may be used to obtain the desired antenna cable loss.

However, installation of the external attenuator is beyond the scope of this STC. Additional

manufacturer's data may be necessary and FAA approval may be required to cover the installation

of an external attenuator.

(4)

The GDL 69/69A Gain/Loss component must be between +6dB and -4dB. If the GDL 69/69A

gain/loss component is outside this range, additional gain or loss must be added between the

antenna and the GLD 69/69A RF input. The factory default setting for the internal GDL 69/69A

component is -0.5dB. The variable attenuation value required to attain the GDL 69/69A gain/loss

component will be programmed into the configuration module during post installation checkout.

See Section 2.6.4.2 for explanation of calculation.

2.6.4.1

Determining Antenna Cable Loss Value

The GDL 69/69A is factory preset with a default cable loss value of 4.5 dB, which is equivalent to 12 to

16 feet of RG-400/U cable with two properly terminated TNC connectors. If the installed antenna cable is

within this length, use this value in Table 2-7. If the cable is different from the default cable, use the

following formula to determine the cable loss value to use in Table 2-7.

Loss in dB = (Length x Loss) + (0.5 x #Connectors)

Where:

For example:

If an RG-400 coax cable is 10 feet long with 2 TNC connectors, the cable loss component is

GDL 69/69A Installation Manual

190-00355-02