The Broadcasters' Desktop Resource

Fun With A Real Flamethrower

[October 2011] You have to love it. Broadcasting with the big transmitters can definitely present the occasional bang – or worse. No wonder we call them “flamethrowers!”

Here is something that happened as part of the growing pains that can occur when diplexing a pair of 50 kW signals into a directional array. Andy Skotdal of KRKO/KKXA kindly shared this video of what they found on one site, and explained what they did to solve the problem.

As you can imagine, it is not an easy task when you are tossing 100 kW around. Not only are there all sorts of networks, both matching and filtering to get “just right,” there were six towers where the problems could originate.

At first they knew only that they had an arc somewhere in the transmission system. Then they found it, perhaps aided by the pungent ozone smell.

As they said on site: “Are you ready?” OK … click on the video.

Video Courtesy of KRKO

The engineers from Hatfield and Dawson were on site and solved this particular arc. Among the steps they suggested to eliminate the problem:

1. Use wider strap but eliminate the excess attached to the tap.
2. Add corona rings to the dead ends of the coil.
3. Strip the paint from the outer edge of the door and box frame.
4. Add copper trim around the door.
5. Ground the door.
6. Bolt the door permanently shut.
7. Retune after modifications.

… and hope for no more arcs anywhere on the site of the 100 kW transmission plant!