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Engineering note

The rack is the part nobody designs

Most installations are specified component by component and then squeezed into whatever cabinet is left. The rack is where the next five years of maintenance happens, so it deserves the same drawing as the antenna.

Start with the heat, not the units

Every unit in the rack produces heat, and a closed cabinet with no ventilation turns a 40 °C machinery space into a 55 °C one inside the cabinet. Consumer-grade electronics derate or fail there, and the failure looks random until the temperature is measured.

Add up the dissipation from the datasheets, then decide: ventilated cabinet with filtered fans, forced extraction, or a small cooling unit. Filtered fans are enough for a headend and an ACU; recorders with spinning disks want more.

UPS sizing in three numbers

Load in watts, required runtime in minutes, and battery chemistry. Runtime is not linear in load — doubling the load more than halves the runtime — so size from the datasheet curve at the actual load, not from the headline VA figure.

Decide what actually needs to ride through: the ACU and the recorder are worth keeping alive during a switchover; the headend and televisions are not. That decision cuts the UPS by half and makes the runtime honest.

Layout rules that survive refits

Put the units that get touched most at chest height, and the ones that never get touched at the bottom. Leave one rack unit of blanking panel between heat-producing units, and one empty unit at the top for whatever gets added later.

Cable management is not tidiness: a rack where the cable can be traced in ten seconds is a rack that gets maintained. Use labelled bundles, and keep the schedule on the inside of the door — a QR code to a document is better than a plastic sleeve that falls off.

  • Heaviest units low, most-accessed units at chest height
  • Blanking panels between heat sources; one spare unit at the top
  • Separate DC feed and signal bundles, labelled at both ends
  • Rack schedule on the door plus a digital copy referenced by QR
  • Spare capacity: one free switch port per VLAN, one free rack unit, one spare PSU

Access is a design input

If reaching the rack means moving stores, nobody will reach it. The room needs a clear 600–800 mm working zone in front of the open door, light at the rack face, and a socket for a laptop within reach of the ACU — because configuring it from a laptop on a cable is still the fastest way to diagnose anything.

Checklist for the drawing and the yard

  1. 01Heat load summed from datasheets; ventilation or cooling chosen from that number
  2. 02UPS sized from the runtime curve at the real load, with a defined keep-alive list
  3. 03Working zone in front of the rack, lit, with a laptop socket at the ACU
  4. 04Labelling consistent with the cabling drawing
  5. 05One free port per VLAN, one free unit, one spare PSU

Questions on this note

Rack planning

Does the ACU need to be in the same rack as the headend?+

Not necessarily, but it needs to be within cable reach of the antenna and in a place an engineer can reach with a laptop. On smaller vessels that is the same cabinet; on larger ones the ACU often lives near the antenna and only the display or network connection reaches the bridge.

How much UPS runtime is enough?+

Enough to cover a generator switchover and a controlled shutdown, not enough to keep television running. Fifteen to thirty minutes at the actual keep-alive load is the usual answer once the list is honest.