Care and Feeding of a Dehydrator

One of my biggest disappointments watching broadcasting evolve is the lack of mentoring programs for entry-level engineers.
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One of my biggest disappointments watching broadcasting evolve is the lack of mentoring programs for entry-level engineers.

All too often, when someone wants to get a start in broadcast engineering, they are shoved into the deep end of the pool, and either sink or swim. Opportunities to learn engineering tricks of the trade at the side of an experienced engineer are more the exception rather than the rule these days. That’s why educational programs are so important.

Manufacturers play an important role in providing education, too. Seminars, training and publications are useful ways to expand your knowledge base.

Andrew Corp. recently sent me a copy of a free booklet that every FM engineer ought to own, "The Biannual Care and Feeding of Your Andrew Dehydrator." This 10-page booklet is chock full of tips regarding dehydrators.

A section on preventive maintenance describes routine procedures that will keep your dehydrator running.

For example, you replace the fuel and air filters in your automobile periodically. When was the last time you replaced the intake filter on the dehydrator compressor? These are to be replaced every six months, and more often if the dehydrator runs in a dusty or dirty environment.

The maintenance booklet has lots of pictures, so you’re not left wondering what the text actually meant. A useful process for checking for leaks in your entire pressurization system is included. The booklet wraps up the subject of dehydrator maintenance by including two pages of troubleshooting tips and answers to common questions.

For example, do you know how to identify the 1/8-inch NPT valve fitting? There’s a chart to help, but the 1/8-inch reference is the inside diameter of the fitting, not the outside.

Winter is just around the corner, and your pressurization system had better be working. Get your free copy of Bulletin 1557 by contacting the Andrew Customer Support Center toll free: (800) 255-1479.


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(click thumbnail)Fig. 1: Bet you can’t find this splice kit in a Cablewave or Andrew catalog.
Take a look at Figure 1. How’s this for a splice kit?

When station personnel investigated to find out why satellite signals were failing, they discovered this "home-brew" splice. Not only had it leaked, but the partially weatherproofed hose clamp was an integral part of the splice.

File this one under "Anything to save money." Include in your calculation the loss of programming and commercials when the satellite signal (and the listeners) went away.


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Laverne Siemens is the director of engineering with Golden West Media in Canada. He writes that the information provided on sinking ground rods was most helpful. Thanks again to all the engineers who contributed their ideas.

Laverne has had success in sinking 10-foot ground rods by hand, wetting the soil, pounding the rod into the ground, working it from side to side, removing the rod to pour more water in the hole and repeating the process.

Usually he’s able to step on the rod to bury the last foot or two. Laverne even taught the procedure to a tower crew, who had previously used the sledgehammer method.

Don Jeerings, John Stortz’ assistant at the Moody facilities in Florida, writes that the proper hardware is necessary when making the ground wire connection from the ground rod to the guy wire. Instead of the more common "U" bolt, use split bolts instead.

The argument against the "U" bolts? The "U" bolt concentrates high stress because the contact area is so small and the pressure so high per unit area. Ground wires running from the guys could fail prematurely because of "work hardening" when secured with "U" bolts.

What is work hardening? You can duplicate work hardening by taking a copper radial wire and bending it back and forth several times. As you repeat this process, you will find that it takes more strength to bend the wire, and the wire will get warm. If you look closely, you will find that the wire is not bending where you started, but the wire bends next to the point where you began the bending.

The initial bend has "work hardened" and become stiff and brittle. The softer part next to the work-hardened portion of wire is the section that is now flexing.

As the radial wire leading from the guys to the ground rod flexes as the wind blows, if the "U" bolt is used, this highly concentrated stress will cause the ground wire to work harden, crystallize and eventually break.

The split bolt spreads the stress over a larger area, reducing the hardening action. It goes without saying that an inspection of guy wire grounding should include a close inspection of the ground wire itself.


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Bill Ruck responded to our picture of a power cord tied neatly to the wall in the Aug. 1 Workbench.

Although it looks pretty, Bill cautions that it’s not a good idea. As his father used to say, "Yes you can, but no you may not!"

Securing a portable cable to the wall is a direct violation of the National Electrical Code. After a couple of times fighting over this with electrical inspectors (Bill lost each round), he has learned the difference between an "appliance" and a "fixture," and wants to enlighten Workbench readers.

An appliance is something that plugs into an outlet. Bill has seen some transmitters fed with electrical range plugs that were considered appliances.

As long as the power cord is free, you can mount the device (for instance, into a rack). However, you cannot secure the power cord to anything except with gravity. Thus, power cords neatly bundled and secured to a tie bar with cable ties are not allowed for appliances.

Power cords run in "D" rings or Panduct probably are O.K. because the mounting is not permanent.

Multiple outlet strips can be considered an "appliance" if they are only supported by gravity, such as sitting on the floor. However, if the strip is mounted in any way (screws, hook-and-loop fasteners, double-stick tape), it becomes a "fixture" that must be connected in a permanent fashion as specified in the NEC.

Following this rationale, a rack-mounted power strip is not an appliance but a fixture, and therefore cannot be plugged in.

Don’t let that inspector inside your portable remote racks! Figure 2 shows a wall wart that is definitely not secured by gravity.

(click thumbnail)Fig. 2: Power cords bundled and secured to a tie bar are not allowed for ‘appliances.’
Now before you dismiss Bill’s caution, be aware that an electrical inspector can shut you down if NEC violations are spotted. Try explaining that to your general manager.

Furthermore, should there be a fire, and the insurance inspector finds NEC violations, you suddenly may find yourself without insurance coverage.

Your best advice: follow the NEC at all times, even though it can be a hassle and cost additional money. National Electrical Code and NEC are registered trademarks of the National Fire Protection Association Inc. Radio World encourages readers to obtain a full copy of the code as a reference.


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Looking for obsolete semiconductors?

Dave Hershberger, principal engineer with ADC Broadcast Systems Division, offered a good tip on the radio-tech page at broadcast.net recently.

Try Rochester Electronics in Massachusetts at (978) 462-9332, or online at www.rocelec.com .


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Bob Hoffman is market chief for Bonneville International’s WIL(FM), WSSM(FM) and WRTH(AM) in St. Louis. Bob offers this tip to anyone who plans to install new audio processing gear, or even a delay system, which could create a bothersome delay for studio talent monitoring the direct air signal.

Bob recently implemented a simple solution, using the Broadcast Tools Smart Silence Monitor.

The air console audio is fed to a sidechain processor and looped back to the studio air monitor through the normally closed contacts of the Smart Silence Monitor relays. This allows the talent to hear a "pseudo air monitor."

A tuner (through a distribution amplifier) feeds the silence sensor input and the normally open contacts of the SSM relays. When an off-air condition occurs, the SSM relays will switch to feed direct tuner audio to the studio monitor, alerting the talent of the condition in seconds.

Bob has wired a second output of the SSM to drive an audible alert in the engineering shop.

Submissions for this column are encouraged, and qualify for SBE recertification credit. Fax your submission to (703) 323-8044, or send e-mail to jbisset@harris.com

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