If you’ve spent some of your nice fall days cleaning your transmitter site, watch what you use for the job.
Kirk Harnack, who works for Telos/Omnia and has a long history of contract work, cautions about the use of powdered substances in transmitter buildings.
(click thumbnail)Fig. 1: Seal spaces around PVC entry pipe to keep out the elements and furry friends.
He gives as an example boric acid products like the brand Roach Prufe. Kirk encountered a site where this product was used by a staff member who thought they were helping. The powder dust was sucked into an FM transmitter, tarnishing everything silver by turning it black. Kirk spent a day cleaning the IPA and PA cavities, sockets and tubes.
Although it was a good day for billable hours, the damage could have been avoided.
The key is to check the ingredient list before using bug bombs, foggers and other products aimed at killing insects.
Tom Osenkowsky, an engineering consultant, has some advice if you are waging a war on bees. These insects return to the nest at night, so spray their nests when it’s dark. Keep the spray from antenna tuning unit light bulbs, which can explode. Buy a box of mothballs and spread a few in each ATU and in the wire troughs in your transmitter building to discourage pests.
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Speaking of contract work, are you having trouble getting paid?
Consider the suggestion of Bob Groome of Wheastone. Set up a charge card account with Visa/Mastercard through your bank. Before you start your work, call for approval for the estimated charge.
If the charge is approved, go ahead with the work. If the charge is denied, head off to your next location. Bob says there is a 2 percent surcharge for the service, but there’s no billing, no chasing slow-pays and no collection problems.
Everyone has credit cards these days, so you won’t waste your time with deadbeats!
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Figure 1 shows the inside of a coupling building. The PVC pipe will protect the sample and RF feed cables, but before the project is finished, the spaces around the pipe must be sealed.
These are the kind of minor points that often get forgotten. Not only will the space provide an entry for nesting animals, you’d be amazed at how much cold air whips through that space on a cold night!
Stay warm, and keep your buildings clean. Plug those holes.
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(click thumbnail)Fig. 2: A Choke on an AM Tower
John Stortz of Moody Broadcasting in central Florida wrote about a tower that one of his FM stations leased from a propane gas company.
The tower was hit by lightning four to five times a year, usually damaging the gas company equipment. Damage included their base radio, power supply and even their fax machine.
Building on his successful grounding at other sites, John made a two-turn coil out of their coax at the base of the tower, then used a Polyphaser ground kit to tie the coax to the tower ground strap. (John is the king of the ground rod, providing a variety of rod driving techniques in previous Workbench columns. )
With this in mind, John drove a ground rod next to their building. That was last summer; so far, there has been no damage from lightning for anyone.
It’s a simple solution with a big payoff. John’s idea is similar to the "choke" seen on most AM towers and pictured in Figure 2. When the tower "spark" or "ball" gaps are properly set, the static charge should jump the gap, rather than enter the coupling network.
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The broadcast engineer needs to be familiar with a myriad of technical regulations. One that might escape you is OSHA noise regulations.
No, your jocks can no longer use a Crown D75 as their headphone amp. Al Gearing, PE, of Mullaney Engineering in suburban Washington offers a site that describes what OSHA is enforcing.
Try out www.osha-slc.gov/SLTC/noisehearingconservation/index.html
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While we’re on the subject of regulations, David Maxon of Broadcast Signal Lab in Cambridge, Mass., wanted to clarify a comment from the Sept. 1 Workbench.
We showed a leaking capacitor, filled with PCB oil, and cautioned, "Don’t become contaminated with it." David points out that personal contamination is only part of the problem. Because the capacitor is no longer intact, it must be treated as a hazard requiring prompt containment and disposal.
Broadcast Signal Lab is a broadcast engineering firm that helps stations comply with technical standards, regulations, RF spectrum rules, RF exposure rules, as well as EPA and OSHA regulations. Although "small" capacitors (less than 100 cubic inches in volume) may be disposed of in the regular trash, the leak changes the situation dramatically.
David ran into a leaking capacitor problem several years ago, and the disposal costs and tracking requirements were astonishing. His advice: correct the problem now, before the capacitors start to leak. The cost of disposing of a leaky capacitor properly is not trivial.
All engineers should reference Title 40 CFR 761, which outlines the PCB regulations.
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Ed Bukont works for CommStruction, a broadcast projects company. Ed is a source of lots of neat products like the Home Depot knee pads that are great when you’re on your knees in front of a transmitter (praying or fixing!).
The Miles Tek brand is another of Ed’s finds. As engineers spend more time handling network and computer problems, this company quickly will become one of your best friends.
Check out www.milestek.com or call (800) 524-7444. The company stocks a variety of networking cable, plugs, voice/data accessories and connectors. It also provides technical information like how to distinguish 50-ohm from 75-ohm BNC connectors.
The product line includes audio/video and wire management. Are you running cable through a plenum? Take a look at their pulley device for making plenum cable pulls a breeze. Tell them you heard about them from the pages of Radio World.
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