Scott Todd is a field technician for Educational Media Foundation, handling stations in Minnesota and Wisconsin.
He needed to remove a “bullet” from an RF elbow and found that it was stuck.
Not wanting to put the jaws of the pliers directly onto it, he wrapped the base of the bullet in four layers of electrical tape, then tightened a small hose clamp around the bullet. This permitted Scott to grab onto the bullet with the pliers, wiggling it free with no damage.
Grout with muscle
Longtime Radio World contributor Charles “Buc” Fitch, P.E., enjoyed the DexPan tip that we shared back in April 2021. You’ll recall that the material can be used to break up old tower piers or concrete pads chemically.
Buc notes the difference between cement/concrete and grout. The former shrinks as it dries. Grout, on the other hand, expands. That’s why it is used between bathroom tiles; it fills the voids.
The DexPan compound essentially is grout with an extreme expansion coefficient. That property is why you can grout anchors into rock but you cannot cement them. The grout swells around the bolt, rod or rebar, pinning it inside the rock void.
Also in that column, we shared an observation about cable pulling out of their connectors with built-in restraints. Buc reminds engineers that the National Electrical Code is specific about cable types, connector types, appropriate applications and installation details for running wires vertically, such as up a tower.
An area of broadcasting subject to this section are tower lighting wires that can run great distances up a tower in conduit. The rough rule of thumb is that no wire installed vertically can travel more than 100 feet before being supported.
Buc was called into a station where electrical metallic tubing (EMT) conduit was run up a dozen or so floors to connect to a rooftop generator. To save money, this had been a do-it-yourself job; but the work all had to be done over because the wire was not supported properly and there were no fire stops installed as the conduit passed each floor landing.
In the wire sizes commonly used in broadcast applications such as tower lighting (18 to 8 AWG), the maximum spacing allowed between supports is 100 feet. Also, the individual wires have to be supported at the top of the run, or as near the top as is possible. Specific support spacing information for other wire sizes is addressed in an associated NEC table.
Buc cautions that the NEC codebook is not a design manual. The “designer” of an electrical system is directed to support the wires wherever needed to avoid stretch, which can affect the integrity of the insulation and companion connections.
The NEC also has pages dedicated to “flexible cabling” — think extension cords. Generally you are not allowed to use a flexible cord in place of permanent wiring. That rack of terminal gear that you use only during football season at your local college pressbox can plug into an outlet with a short flexible cable. But you can’t go out the door and down the hall into the janitor’s closet for months at a time to get power; that requires permanent wiring.
Keep in mind that every extension cord used in your engineering efforts is a flexible cord and subject to the 12 AWG minimum sizing. Definitely no splicing is allowed on any flexible cord.
To protect yourself, if a flexible cord — including any extension cord — is damaged, replace it.
Jose Rodriguez is a technical manager at Tektronix, which makes a variety of test equipment but is probably best known for their oscilloscopes. His team has prepared a great video explaining how to display an electronic signal properly once it’s captured.
Seasoned engineers will know that the secret is in proper adjustment of the horizontal, vertical and trigger controls on the ’scope. The five-minute video will help entry-level engineers alleviate the mystery of how to set one up. The video is a refresher for us seasoned engineers, too.
On the resource page, the video is at the top right. An Oscilloscope Fundamentals paper and other resources are also available.
John Bisset, CPBE, is in his 32nd year writing Workbench. He handles western U.S. radio sales for the Telos Alliance and is a past recipient of the SBE’s Educator of the Year Award.
Workbench submissions are encouraged and qualify for SBE recertification credit. Email [email protected].