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Workbench: A Good-Looking Weld Is Not Always a Good Weld

Also, here’s an industrial and business surface sterilizer (if you can get your hands on one)

Broadcast contract engineer Tim Walker wrote in to say how much he enjoyed reading solutions to problems from engineers in the field in past Workbench columns. It’s reassuring to see the display of engineering talent visible in the pages of Workbench.

Tim shares an experience with a Collins/Continental “Power Rock” 5 kW AM transmitter. This is a pulse-width-modulated transmitter that, in Tim’s case, was intermittently losing modulation of the RF envelope.

The culprit turned out to be a broken connection to the grid of the triode switch modulator tube (Fig. 1).

Fig. 1: With power off and circuits discharged, test the security of connections.

The soldered connection appears solid but was in fact broken, making intermittent contact with the grid ring as the temperature fluctuated and it vibrated from the high volume of cooling air through the tube compartment.

When Tim finally identified the problem, he was reminded of the welder’s adage:  “A good-looking weld is not always a good weld, but a good weld always looks good.” The same applies to electrical connections, so take nothing for granted when tracking down intermittent problems.

Early in my career, I was working with a consulting engineer, brought in by the station to try to determine why the transmitter would occasionally shut down, while the directional parameters went nuts.

The consultant and I walked to every tower. Using a long wooden broomstick, he rapped components in the base antenna tuning units, followed by a good rap to the coiled copper tube feedline to each tower. The station chief monitored operation and communicated the status over a two-way.

On the third tower, when the consultant whacked the copper feed tube, it broke right off the tower! The weld “looked” OK, but a good-looking weld is not always a good weld.

Connections need to be secure. This is especially true in older AM arrays.

Tip: Don’t Touch!

Projects engineer Dan Slentz and I were remembering the days of the big 50 kW transmitters, and the way the coils would “sing” with the modulating signal. You could actually hear the demodulated signal singing inside the transmitter, as well as in the tuning units at the tower base.

Dan found a memorable video on Reddit to share these memories with Workbench readers.

 

Still from Reddit video of an incident at a hot AM tower
Fig. 2: Check out this video on Reddit, titled “Never touch an AM radio tower.”

This would be a good video to post for your entire staff to watch. Hearing the advertisement’s phone number as the battery cable is arcing across the tower base is nothing short of amazing to someone who hasn’t experienced it.

The fact that you “work” on this stuff as a broadcast engineer should amaze your staff as well. Show it to them! Just another day in the life of a broadcast engineer.

Tip: UV sterilizer

Griffin Communications’ Radio Engineering Director Brett Gilbert, researching a simple way to decontaminate surfaces, found an interesting product from CureUV.

The company specializes in ultraviolet light sources that sterilize surfaces. One particular model that looks promising is the GermAwayUV Premier 35 Watt Handheld UVC Surface Sterilizer.

This handheld device is about the size of a cigar box and is supplied with a 6-foot AC cord. It is smaller than CureUV’s other industrial sterilizers and is priced at under $400 list. The device will effectively decontaminate surfaces from viruses, bacteria and molds.

CureUV Sterilizer
Fig. 3: This is one way to make sure your surfaces are clean.

It provides a quick and easy way of sanitizing surfaces, as you plug it in and slowly pass the lamp over the surface to be sanitized.  The bulb lasts up to 10,000 hours (about 1 year). In addition to the UV-C emitting bulb, brightened reflectors enhance the accuracy by up to 30%.

UV-C light is ultraviolet, in the C spectrum, and is especially efficient at destroying harmful microorganisms. In addition to being effective against a range of viruses, the UV-C light can be used to remediate mold, quickly killing mold spores.

UV-C light has a range of applications both residential and industrial. It’s used in food preparation settings to reduce contamination, as well as in hospitals, clinics and veterinarian offices to sanitize surfaces. The company offers a caution that Ultraviolet UV-C light is harmful to your eyes and skin, and users should never look directly at the bulb. The company recommends the use of safety glasses that can be ordered with the device.

But how do you know it’s working? As I read the description, that was my first question; I wondered whether this was snake oil.

The company acknowledges that this is a natural question, since disinfection is happening at a microscopic level. It includes a set of UV-C Visualizer Strips along with all GermAwayUV Surface Disinfection products. You place the UV-C Visualizer card on the surface you wish to disinfect and run the handheld sterilizer over it. The yellow strip on the card will change from a bright yellow to a light green.

Exposing the surface to the UV-C light until the strip turns green will ensure the surface has been treated properly, the company says. If there is no color change, you have to slow the rate at which you move the handheld sanitizer across the surface, or move the sanitizer closer to the surface.

The website was citing a shipping delay of eight to nine weeks at this writing. If you or your station invests in this device, please drop me a line to tell readers how it works out.

John Bisset has spent over 50 years in the broadcasting industry and is still learning. He handles western U.S. radio sales for the Telos Alliance. He holds CPBE certification with the Society of Broadcast Engineers and is a past recipient of the SBE’s Educator of the Year Award.

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