Efficient Use of Rack Space
Jan 1, 2015 9:00 AM, Doug Irwin, CPBE AMD DRB
Rack space is often a very precious commodity at a transmitter site. Naturally one will load up equipment in the front of the rack, but if you think of the rack as a cube, what about the other sides? Can they be used in some fashion? Let''s take a look at some ideas on how to get more stuff in a rack and making the best use of that �real estate.�
In my very first tech tips, I wrote about using the sides (as some call them, the �cheeks�) of a rack for various functions. When you have racks mounted side by side, it''s easy enough to use that interior space by mounting pieces of 3/4-inch plywood on the inside of the rack, oriented vertically. Paint them black to make them far less noticeable. These pieces of wood are great for wire management or facilitating the installation of small devices such as matchboxes, �stick-ons� and the like. The last thing you want to do is waste rack space for those. After the front of the rack, the back is probably the most convenient place to mount other things, but it''s obvious that space has to be used judiciously. You can load up stuff in the back of a rack (assuming you bought it with rear rails, right?) but you need to leave a convenient means to reach through and get to the back of the gear that is mounted in the front of the rack. The rear rack rail space has limited uses, for sure. Take a look at Figure 1.
Figure 1: STL With Filter and Duplexer
Notice a couple of things here. First, the rack rails are pushed in far enough to allow for an outlet strip to occupy space at the very back of the rack. The reason behind this is simple: If you push those outlet strips too far in, deeper rack-mounted gear might get in the way of some outlets.Second, you might well recognize the rear end of a Moseley 6000 series STL transmitter in this picture. Since the RF output is on the rear of that unit, it makes sense that related RF components are also in the back of the rack, mounted to the rear rails. What you see in this picture is a 950 MHz duplexer, as well as an ISM band transceiver and injector. Note that there is nothing directly behind the Moseley. In the front of the rack behind the cans of the duplexer is space for either rack blanks or a piece of gear that isn''t very deep. They don''t physically interfere with one another.
Another item that mounts well on the rear rack rails is an Ethernet switch. From a cable management standpoint, the reason for this is pretty obvious: While almost every device with an Ethernet port has it on the rear panel, the switch generally has all of its ports on the front. Putting the network switch in the back of the rack simplifies cable management. See what I mean by looking at Figure 2.
Figure 2: Network Switch, Patch Bay and Krone Block
Here you see an Ethernet switch mounted in the rear of the rack. Note that other interconnecting devices such as the RJ-45 patch bay fit nicely in the back of the rack as well. Krone blocks (or whatever your preference is) can easily be mounted to blank rack panels for additional interconnects such as audio and remote control.A common mistake (usually not discovered until later in the build process) is using rack panels that are too large. They invariably block too much access to the front of the rack. Blanks or devices occupying one or two rack units usually work fine and will not keep you from accessing gear mounted in the front of the rack, as long as you space them out. Make sure you can get your arm through the spaces between components mounted in the rear of the rack.The top of the rack is a space that many don''t think of, but it has its uses as well. See Figure 3. In this particular instance, it made sense to mount a four-port RF switch right in the top of the rack. This was part of a project to add a backup transmitter to a site that previously had just a single transmitter. As you can see, a large round hole was cut in the top of the rack, and then the switch was mounted on four bolts. The transmission line ran right above this rack, so all that needed to be done was cut it, add elbows, then attach the elbows to the switch. The four bolts facilitated leveling to align the transmission lines with the switch perfectly. The location of the four-port switch limits the depth for items that are placed at the very top of the rack, of course. The solution is to put items that are not very deep at the top of the rack. In our case, it was a wattmeter panel.
Figure 3: Four-Port Switch Mounted in the Top of the Equipment Rack
It''s typical just to consider racks as two-dimensional devices; but with a little planning, strategy and three-dimensional thinking, you can get a lot more in them.