Motorola LM100 Operations Instructions download pdf (Page 17)

Overview 2-5

GX2-LM1000E* Installation and Operation Manual

Additional Features

Functions performed by the GX2-LM1000E* include:

 Precision thermoelectric cooler (TEC) maintains the laser at a constant temperature

 RF overdrive cutoff circuit protects the laser from excessive input levels

 Provides local alarm indication by changing the color of the front-panel

STATUS LED

 Stores module identity, laser operating parameters, and set-up information in NVM

 Downloadable firmware to support field upgrades

 Factory birth certificate stored in NVM and accessible through local interfaces

RF Section

The RF input signals are applied to the GX2-HSG* equipment-shelf rear panel. The upper

connector is the main-broadcast input. The lower connector is provided for narrowcast input and

requires a 6 dB higher input signal level than the main input to produce the same output level

as the main. The narrowcast input is a convenient method of adding channels to serve select

areas of the cable plant. The narrowcast input must be terminated in 75 ohms when not in use.

Both inputs provide full bandwidth.

The main input test point (

RF TP 1) is located directly at the main input connector. This enables

verification of the input signals with the highest possible accuracy.

Low noise, low distortion gain stages amplify the input signal to the optimum drive level

required for the laser. A programmable PIN attenuator, located midway in the amplifier chain,

is controlled by the microprocessor and, in turn, controls the drive level.

Following the final gain stage is a calibrated RF test point (

RF TP 2). This test point provides a

reliable secondary indication of modulation.

A sample of the RF level is detected after the final gain stage. The output of the RF level

detector is a DC voltage level that corresponds to the total signal power applied to the laser. To

protect the laser, the laser drive signal automatically cuts off when the RF drive level exceeds a

safe limit.

A calibrated table of RF power meter voltages is stored in NVM and is used by the AGC modes.

When in Preset mode, the microprocessor references laser characteristics stored in the NVM

and adjusts the PIN attenuator to apply the optimum RF level to the laser. The power meter is

constantly monitored and the PIN attenuator is adjusted to maintain a constant drive level into

the laser.

Other AGC modes operate in a similar manner but use different laser drive level reference

points, as set by the user. These are described in the previous subsection “Operating Modes.”

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Motorola LM100 Operations Instructions Page 17