Computer and Audio Racks for Amateur Radio

As I start moving my main station from the QTH we are selling to our new QTH 12 miles west, I’ve wanted to put my Flex-6700 Station into a rack.

I’ve not found an all-in-one information resource on how to do a cost effective rack design.

So I’m going to hammer the keys with the tidbits I have picked up and hopefully these notes will be helpful for someone else.

Rack vs Cabinet:

Racks are framework, where a cabinet has solid sides.  A cabinet may have a solid/removable back, and sometimes a hinged front.

As I want to be able to access both fronts AND backs of my station gear, I’m going with a Rack rather than a cabinet.

Fixed Floor vs Fixed Wall vs Rolling Floor:

A rack can be on castors in Rolling Floor versions or in fixed configuration.  If fixed it can be loose or attached to the floor or bolted to the wall.

Consider what your flooring is like and your expected total rack weight as you decide fixed or rolling. If conditions allow a Rolling Floor model suits a radio station well.

In my case I expecting less than 200 Lbs of gear in the rack and the new radio room flooring is sturdy stuff, so I’m going with a Rolling Floor model.

Height:

First what is a “U”? Standard racks are sized in U’s, where each U is 1.75 inches high.

So a U is 1-3/4 inches.

While second nature to rack regulars, here is a quick list of the first eight U’s for their total height:

1U = 1.75″
2U = 3.5″
3U = 5.25″
4U = 7″
5U = 8.75″
6U = 10.5″
7U = 12.25″
8U = 14″

Remember to include feet and other parts affecting the height of something you are evaluating when sizing it.

Also always allow the manufacturer’s recommended airspace around a piece.

I made a sketch of how I want to stack my station gear, and allowed for the LARGEST U numbers for positions where my back-up gear and main gear differed in height.  I settled on a 27U rack, which is a nominal 4 ft rack to put it in perspective.

Width:

The most common rack standard is 19″ between the rails.

There are other common widths.

Depth:

Here things are sketchy.  You can find 19″ wide racks ranging in depth from 10″ all the way to 42″ deep.

Some rack units are adjustable as well!

So you have to look at what your deepest equipment needs, adding for connectors and cabling, to size your rack.

Again, Your deepest piece of gear plus connector space sets your depth.

In my case I’ve settled on a 24″ deep rack.

Posts:

Racks come 2, 4, 6 and center post configurations, and some have a slight slope back to their face if they are intended for Audio Recording use.

If everything in your station gear is not “rack ready” needing to be put on shelves, a center post rack configuration with enough shelves can meet the needs really well.

Typically for a serious station, one with power supplies and amps, a 4-post rack is effective.  “Rack ready” gear is fitted right in, and shelves can be added to hold anything not rack-ready.

The 2-post racks are light duty racks for the most part.

Weight is consideration, so you need to size your rack to carry the expected weight.  Heavy duty racks sometimes are 6-post versions.

As I am rack mounting power supplies and putting my amp in the rack, I’ve gone for standard duty 4-post rack.

Rackability:

Some amateur radio gear is “ready to rack,” sometimes you can get optional rack kits, and some its “rack ready” and needs to be on a shelf.

Some gear may not be “rack ready” but accessory kits may be available to add rack-ears or fit the gear to rails converting it to rack-ready.

To lay out your rack configuration you need to assess each item of gear for its rack-readiness. 

My station has a mix of rack-ready and gear needing a shelf in it.

Shelves and Rails:

Shelves can use the cantilever of their rail mounts to support themselves.  These usually hang just from the front posts. Cantilever shelves may be 1U, 2U or more to create the leverage they need to support your gear.

Others attach to all the corner posts, and may be adjustable for exact fit.

Shelves for center-post racks can but two part to fit around the center posts.

Shelves may be solid, vented, flat, lipped, full-sided, or pull outs.

Rails adapt gear to your rack, and can either pull out or be fixed.  Some have cross bars and some are adjustable.

Some pull out rails and shelves have cable management arms and features.

For the most part radio gear that is not rack-ready goes on shelves.

To select a shelf consider the shelf type, equipment weight, depth, and whether ventilation is needed.

In my rack I am using several vented adjustable 2U cantilever shelves and a single 50kg rated solid 3U shelf for my amp.

I have nothing needing rails going in my rack.

Nuts, Bolts, Screws, Washers and Bits:

Rack holes come in several flavors.  Round Plain, Threaded, and Square Holes are common.

Round Plain holes expect that a machine screw passes through the actual rack and is captured by a separate nut.

Threaded holes let the rack frame act as the nut as the machine screws thread directly into them.

Square Holes are used with a caged nut that is fitted into holes in use.

New hardware is largely Metric, often M6.

In Rack terms Bolts and Screws are interchangeable words for the same item.

Washers are needed to avoid “Rack Rash” where the hardware marks and perhaps damages the equipment when it is attached.

Bits are important, as you can find rack hardware heads in slotted, Phillips, x-cross, hex, square drive, and security-bit versions – maybe even more types if you look around!  One tip I was told was to put one of the bits and perhaps some spare hardware in an old pill bottle zip-tied out of the way on the rack for future use.  Would seem to make sense if your hardware needed a specialty bit.

Power, Ground, and Ventilation:

Both rack-mount power supplies and rack-mount mains power distribution devices are available. Watch out as some computer gear uses plug configurations not common for radio gear.

I’m including a dual Astron power supply and a surge-protected 120v rack-mount power strip in my design. I am direct wiring the 240v single phase for the amp.

Research hasn’t come up with a clear conclusion on whether to ground the rack and ground the equipment to the rack, to let it all float perhaps including some isolation, or whether to ignore the whole grounding issue.

I’m adopting the telecom idea of bonding everything for now.

If your rack is going to be tight, going to be exposed to heat/cold or if you picked a cabinet you may need to add forced ventilation.

If it is going in your shack and is an open 4-post you likely will be okay.

Rack Orientation:

With ham gear having a lot of back side connections you will want to make sure you’re going to have access to the back as well are the operating face.

Some hams work any gear they have to regularly access from the side of their racks, so be creative with shelf mounted gear making it work for you.  The actual rack mount stuff you are kind of stuck with.

I’m planning on having my rack “sideways” with the few items I do need to access showing out the side, as the majority of my gear doesn’t need to be accessed that often.

Other Rack Accessories:

The sky is the limit as you can include drawers, lockable “glove compartment” things, lights, extendable keyboard trays, special built 1U to 3U computers, security add-ons and more.  Then there is cable management arms, conduits and attachments.

I’m hoping to have a dust cover built for my rack.

Partial Rack sizes:

I was confused until I caught on that if a piece of gear is said to be 3U half-rack at 16in that it seems to mean that it is really 3U high, but is 9-1/2” or less in width and really is 16” deep.  I’ve only seen this description used once on ham radio gear.

Weight goes Low:

Obviously if your rack is floor or wall attached this isn’t so important, but if it will be on wheels keeping weight low will help stability.

My power supply and amp will be at the bottom.

Re-purposing Old Radio Racks and Telecom Racks:

Not all telecom racks mesh with computer/audio rack standards and likewise older radio racks may not either.

Rack Security:

Your equipment can be installed with tamper-proof screws and security strapped to the rack frame   Your rack can be similarly bolted down or cabled to the structure.

You can also incorporate motion sensors and other devices.

I’m not describing my rack’s security here though.

Can you build your own rack?

Without some serious metal forming equipment it would be hard.

But it is possible to buy rails with holes ready to fit into whatever rack you build or in a cabinet.

Steel or Aluminum?

Racks come in both.  For our station use either looks to fill the role. I’m using Steel.

About those Castors:

Locking, low-mar, carpet, and other specialty castors are available.  If your rack comes as a kit, most likely you will want the locking castors at the front.  Very heavy racks may have extra castors to spread the load.

Where can you get more rack help?

Both Musicians Friend and Sweetwater Audio have a lot of good information on their websites.

https://www.musiciansfriend.com/

https://www.sweetwater.com/insync/racks-rack-cases-buying-guide/

In the end I bought mine from Amazon though.

73

Steve
K9ZW

4 thoughts on “Computer and Audio Racks for Amateur Radio

  1. John B. KD0SFY says:

    “As I want to be able to access both fronts AND backs of my station gear, I’m going with a Rack rather than a cabinet.”

    You can do that with both racks and cabinets.

    “A rack can be on castors in Rolling Floor versions or in fixed configuration. If fixed it can be loose or attached to the floor or bolted to the wall.”

    If you are in an area where there are quakes, bolt it to the floor or for more active areas, the floor and one wall.

    “In my case I expecting less than 200 Lbs of gear in the rack and the new radio room flooring is sturdy stuff, so I’m going with a Rolling Floor model.”

    You might also consider a transit case style of mobile rack, often called a roady case, ATA case, or flight case. They can be had in a variety of heights from 1 RU to over 20 RU.

    “First what is a “U”? Standard racks are sized in U’s, where each U is 1.75 inches high.

    So a U is 1-3/4 inches.”

    Correct. Another thing is the holes (usually three per RU or U) are not evenly spaced. If you look closely, you will see the holes where one RU ends and the other begins are only 0.5″ apart whereas the other holes are 0.625″ apart. When people ingore that, they end up splitting RUs and the holes in their equipment won’t line up correctly with the holes in the rack rails. This is called “splitting an RU” and red flag to those who know better.

    “The most common rack standard is 19″ between the rails.”

    Not quite. The 19″ is the overall width of the bracket. The center to center hole width is 18.312″ and the inside width between the rails is 17.72″. See TIA 310.

    “New hardware is largely Metric, often M6.”

    M6 is becoming more common, but make sure you have the correct screws/bolts/nuts/washers as #10-32 hardware is still extremely common, especially in the US. Another frequently seen size is #12-24. Know what you have and make sure it all matches.

    IMPORTANT: You do not need to make the rackmount screws very tight. Snug is more than sufficient. If you use an electric screwdriver, set the clutch to almost the lowest setting.

    “Power, Ground, and Ventilation:”

    Ventilation is a biggie. I constantly see racks where the equipment has not been laid out to take airflow into consideration. Leave at least 1 RU between items that use convection cooling. Remember that hot air goes up. DON’T BLOCK AIRFLOW! I see this a lot and then people have to add fans to keep their equipment from burning up, when often simply leaving enough space would have addressed the issue.

    “Research hasn’t come up with a clear conclusion on whether to ground the rack and ground the equipment to the rack, to let it all float perhaps including some isolation, or whether to ignore the whole grounding issue.”

    Though many in the industry still use the rack as a grounding busbar, the copper of a real busbar is a much better conductor. The best practice is to use a dedicated copper busbar connected to the ground. Then ground everything, including the rack, directly to the busbar. NEVER rely on rackmount brackets and screws to act as a ground as you can never be sure of the amount of contact you have, which will affect the current capabilities of the contact. Use the correct size wire, ideally stranded, with compression (crimp) fittings — never crimp on solid wire.

    For good information, try Middle Atlantic (www.middleatlantic.com), Great Lakes (www.werackyourworld.com), or Chatsworth (www.chatsworth.com). They have lots of things like white papers and tutorials. Music stores like Sweetwater or ProAudio.com are a good place to buy stuff, but they are definitely NOT rack/cabinet experts, whereas the three I listed definitely are.

    As you can probably tell, I do this stuff for a living. ;)

    • k9zw says:

      Thank you! Do you have any other suggestions?

      73

      • John B. KD0SFY says:

        Here are a few more items:

        Cable management is another area to consider. Look into vertical and horizontal cable management products. Try to avoid using zip ties (AKA cable ties) — instead use hook and loop ( AKA Velcro) strapping. You can get 25′, 50′ and 75′ rolls that are 1/2″, 5/8″, or 3/4″ wide and they are hooks on one side, loops on the other. Cut to length. Zip ties can crush cables (especially coax, Cat 5, and fiber optics), are generally not reusable or repositionable, and can leave nice sharp edges that are just waiting to slice an arm open the next time you have to reach inside. Flush cuts (not regular diagonal cutters) are a must with zip ties.

        Shelves can be positioned with the brackets underneath or above the flat part of the shelf, which can come in handy sometimes. Use a vented shelf if you can, but keep in mind they may sag a bit more than a solid shelf. Sometimes you can bolster them up with a lacing bar. You can use the same hook and loop strapping to attach items to many types of vented shelves.

        The use of blank panels can make for a neater appearance, but exercise caution: They block airflow, so if your equipment is convection cooled, don’t use them. If the equipment has front to back or side to side internal airflow, blank panels may be ok or even necessary, depending on the thermal management scheme employed in your shack.

        If modifying blank panels for mounting things like a RigRunner, coax feed thru, etc. get powder coated aluminum, not steel and not anodized aluminum. You will find it is much easier to work with. If you do use anodized aluminum, prep any cutting or drilling area by removing the anodizing in that spot by applying commercial grade degreaser and letting it set for a while.

  2. k9zw says:

    While I will leave all the comments in place, much of what has been added is important enough that I will be editing it back into the original post. The contributor will be credited.

    Very much appreciate the super helpful comments left and those that also arrived by email.

    Hoping that this summary helps more than a few fellow hams along the way!

    Thank you and 73

    Steve
    K9ZW

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