As a contract engineer, John Ramsey has to carry around a lot of tools and various pieces of test equipment. Rather than store gear on the back seat or risk it rolling around in the trunk, he uses old GPS and camera cases, which he buys for next to nothing at tag sales.
Fig. 1: Delicate or small gear can be carried safely in these cheap, ‘gently used’ GPS or camera cases.
Fig. 2: A GPS case could have been made specifically for the Qbox tester.
They are a great way to store fragile test equipment. The cases are well padded, yet zip or snap open easily.
In Fig. 2, an old GPS case protects a Whirlwind Q-Box analog tester. The well-padded camera case in Fig. 3 neatly holds a Ward-Beck Bit Spitter and Bit Buddy and their associated power supplies.
Fig. 3: The camera case holds not only instruments but also their power supplies.
Small cases like these come in handy for all kinds of things. When I did contract work, a plastic Sennheiser mike case served to hold all my clients’ key chains. It snapped shut and fit nicely under the seat of the vehicle. I love John’s idea of picking these cases up at tag or yard sales.
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Consulting engineer Robert D. Culver offers thoughts for our discussion about securing signage on tower fences.
To begin with, Bob suggests mounting the signs on the inside of a chain link fence. This way, the sign is viewable through the fence.
Attach the signs with tough plumbing strap and bolts with locking nuts. The bolts can be turned from the outside; but the lock nuts cannot be backed off by someone on the other side of the fence. The bolts need not even be tight; just leave them semi-loose to twist uselessly under the vandal’s grip. Someone might cut the strap; but without access inside the fence, they won’t be able to remove the signs from the site easily.
If all else fails, mount the sign on a pole a few feet inside the fence or on any other structure. As long as the sign can be read from the fence, you are OK from the RF exposure point of view.
But Bob poses an important question: There is no uncontrolled RF exposure in excess of the FCC limits outside your fence, right? If that is not the case, move your fence out. The signs are still OK if mounted inside.
Bob also has a question for our readers.
He’s had a repeated problem with a broken neutral power reference in a domestic single-phase 120/240-volt service. He has had limbs fall across the suspended service entrance wires and break the neutral/messenger cable. This is the cable that is under the physical weight load of the cables.
In this failure mode, neither of the two hot legs breaks. Without the neutral reference, depending on the load imbalance on the two hot legs, one side goes low and one goes high. The high side often is above 140 volts and things start to fail. Then the load on the high side gets less, and the voltage goes higher still.
It gets expensive in a hurry.
The insurance company has paid for damaged equipment but it is not amused; the failure has happened three times in about five years. The new insurance policy this year indicates they may not pay for future claims.
The power company just yawns at the problem and will not trim the trees or take other preventive action. Bob has asked them to put breakaway connections at the stress points so that if the messenger cable breaks, the two power legs are pulled free and disconnected. No luck.
So Bob’s question is whether you know of something like a two-pole voltage-sensing circuit breaker that would open the circuits if the imbalance between the legs went beyond some limit. He’s in search of something efficient but simple and inexpensive.
Bob has used large MOVs across the lines. They start to conduct on the high-voltage side, then fail in short-circuit mode. They do not draw enough current to trip a 200 amp breaker before they vaporize. The system needs to pass 120/120 volts but then trip if unbalanced, for example at 105/135 volts. Ideally it would be voltage-time sensitive so as to allow start inrush voltage sag for some heavy demand single-phase loads.
Fig. 4: The Fluke 376 includes the iFlex flexible current probe, which expands the measurement range and lets you measure around awkward-sized conductors. Any thoughts? E-mail me at [email protected].
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Just when you think there can be no further innovations in test gear, Fluke hits another home run.
Its Model 376 Clamp Meter is useful for broadcast engineers, but when cables are bundled tightly, you may not have enough room to separate one enough from the others sufficiently to get the clamp around it. Fluke’s solution is the iFlex. It’s ingenious, one of those things that make you ask, “Why didn’t I think of that?”
Fluke has a cute little video that demonstrates how it works. See it at www.fluke.com/fluke/usen/support/demos/.
Thanks to Bruce Roberts, engineering manager at the Apex Broadcasting stations in South Carolina, for sharing the link.
John Bisset marked his 40th year in radio in broadcasting recently. He works for Tieline Technology and is a past recipient of the SBE’s Educator of the Year Award. Reach him at [email protected] or (603) 472-5282. Faxed submissions can be sent to (603) 472-4944.
Submissions for this column are encouraged and qualify for SBE recertification credit.