Cisco Model D9479 Gigabit QAM Modulator Installation Guide

Chapter 2 Installing the Dual SFP GQAM

78-745431-01 Rev E

Stacking Guidelines

The GQAM is a high-density, high performance device for digital broadband data

delivery. One GQAM performs the services of 16 QAM modulators. This space-

saving feature makes the GQAM the device of choice for contemporary digital

broadband delivery systems.
Providing proper ventilation and cooling for the modulator is mandatory. You can

stack up to 32 GQAM devices in a standard 40-rack unit (RU) equipment rack if you

read and carefully follow the guidelines provided in this section and later in this

chapter.
Each GQAM contains three dual fan packs that provide forced air cooling. These fan

packs, located on the side of the unit, pull air across the internal circuitry to remove

heat.
Important: In order for the fans to operate correctly, you must install each GQAM

using the rack mount brackets included with the unit. These brackets contain

notched cutout sections to allow for clearance so that air can enter and leave the unit

without restriction.
When you install the GQAM in the rack using the rack mounts provided, you can

install them directly above and below each other with no requirements for vented

spacers. Using these rack mounts also provides support for the modulator. The

GQAM is not intended to be suspended or “hung” in the rack by only mounting the

front bezel support.

Controlling Operating Temperature

CAUTION:
Headend equipment is designed to operate in a maximum 122°F (50°C)

environment. Specifically, this means that the air temperature at the air inlet

of any GQAM must never exceed 122°F (50°C).

Each GQAM draws up to 151 W of input power and a total of 515 BTU/hr. For a full

rack with 32 units, the sum total is 4832 W per rack, or 16,480 BTU/hr. You should

make your HVAC considerations based on these calculations.

Controlling Exhaust Air

Exhaust air management is the key to cooling multiple modulators in a custom rack

configuration. Inlet air temperature should be as cool as possible and should never

exceed 122°F (50°C). Exhaust air should have little or no restrictions. Obstructions

such as cabling or other devices that block airflow to the side or top of the rack

should be avoided.