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A Look Around, Once Inside the Transmitter Site

We continue our visual inspection

In our previous column, we covered what to look for as you drive up to the transmitter site building. Now let’s take a look inside.

First, if you don’t have an emergency flashlight with fresh batteries right inside the door, make that a priority. Showing up at a site at night, with no power, can be a dangerous proposition. Keep a flashlight right inside the door as good insurance. Many hardware stores sell inexpensive bright LED flashlights. Figs. 1 and 2 show a model found at Ace Hardware.

Pictured in Fig. 3, Walgreens offers a light that looks like a light switch, and includes a variable brightness control. This particular LED light has a magnet on the back, making it convenient to stick on steel walls, conduit or steel door frames.

Once inside the building, if everything is operating normally, take a set of readings of your critical on-air equipment. If you don’t like paper logs, snap pictures of the test meters. You want a set of “normal” readings that can be compared when a problem arises. This composite set of readings is not just for the transmitter but includes the STL gear, audio processor and any other critical equipment. On subsequent visits, before adjusting anything, check these readings. They become your baseline for normal operation.

Make sure the readings include power supply voltages too. Power supply component failures can cause a multitude of problems. If you know what’s “normal,” a problem can be diagnosed more easily.

Next, use your ears, eyes and your sense of smell and touch.

Does a high-power transmitter blower motor have a squealing bearing? When you entered, did you notice a rodent scurrying for cover out of the corner of your eye? Is there a burning smell or over-heated insulation smell? And if you have rigid transmission line, are the elbows and junctions warm or hot to the touch? Do you know which LEDs or pilot lights indicate normal operation? Again, snap a picture of normal operation of these lamps, using your smartphone’s camera.

Do you have a flowchart for your signal paths? A notebook outlining signal paths and equipment for each site can be invaluable, as displayed in Fig. 4. Dwight Morgan, broadcast engineer with Entravision Phoenix, shares this with Workbench readers. The notebook also allows Dwight’s boss, VP of Engineering Rick Hunt, to identify the signal paths for all the equipment in any of the Entravision chain of stations.

Readers who follow this column know the advantage to having drawings and standardizing on-site equipment as you upgrade. The process just makes maintaining equipment easier. Keeping an eye on operating parameters can also help identify future problems. We’ll continue our inspection in our next column.



If you built, or are in the process of building, the Audio Controlled Switch shown in the March 14 issue of Workbench, note that the schematic contained an error. Thanks to the keen eye of faithful reader Ron Jones, K7RJ, for spotting the error.

Pins 4 and 10 must be connected to Pin 14 (+5 Volts) for the circuit to function properly. The corrected schematic is shown in Fig. 5. Our contributor Frank Hertel wanted to apologize to readers for making this “elementary mistake,” as he terms it.

If you find yourself building circuits, try this trick that I learned years ago from the engineers at the home of the OIB (Operating Impedance Bridge), Delta Electronics.

As each wire is connected on the breadboard or soldered on the perf-board, trace that wire on your schematic with a bright yellow highlighter marker. When you have completed the wiring, check to make sure every wire or connection on the schematic has been highlighted. This process is particularly helpful when building complex projects, as it reduces the chance of a wiring connection being missed. Hope this helps!

Contribute to Workbench. You’ll help fellow engineers and qualify for SBE recertification credit. Send Workbench tips and high-resolution photos to [email protected]. Fax to (603) 472-4944.

Author John Bisset has spent 48 years in the broadcasting industry and is still learning. He handles western U.S. radio sales for the Telos Alliance. He is SBE certified and is a past recipient of the SBE’s Educator of the Year Award.