Fig. 1: A typical GOES satellite yagi from Samco. I was speaking with David Sanford with Texas-based Samco Antennas about RPU antennas recently. Our discussion migrated to vandalism at stations.
David said his company’s antennas are not immune to this problem. Samco makes a Geostationary Operational Environmental Satellite (GOES) yagi antenna, pictured in Fig. 1, used by the U.S. Geological Survey in monitoring streams and rivers. Data is transmitted from sensors in the body of water by satellite to the USGS facility for display and analysis.
It seems that tower lights and transmission line aren’t the only target some misguided hunters like to use, as you can see in Fig. 2. What’s amazing is that with more than half the GOES antenna blown away it still worked. Got an interesting photo from the field to share? Send it to me at [email protected].
Samco makes a rugged and reliable RPU yagi that isn’t top-heavy and will work well with Will-Burt Hurry-Up masts. Contact your favorite dealer for more information, or head to Samco’s website for data sheets: www.samcoantennas.com/products.html.
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John Huntley is chief engineer and director of IT for the four-station Cumulus cluster in Rockford, Ill. He writes that he has been using a Fluke 62 Mini Infrared Thermometer for a few years without any problems. You’ll find a variety of Fluke meters at the Grainger website. Click on the Radio World Links page at radioworld.com/links to see what’s available.
John’s unit has a spot/distance ratio of 1:10 (where at 10 inches distance, you measure a 1-inch spot). John reports that this instrument works just fine in the presence of 5 kW at 1440 kHz.
Our recent article in RW reminded John to check his ATUs and phasor again. He verified there were no heating problems with the RF connections or components. John did verify a capacitor failure in a phasor using his IR thermometer a few months ago. The AM directional readings were wrong and the IR thermometer found the hot capacitor.
Winter’s not that far away; John says he makes sure he has the instrument with him to check the generators at the transmitter sites for coolant heater failures. He concedes that while a hand works fine (a touch test for heat), sometimes he will use the IR thermometer to check for heat in the radiator from the outside of the cabinet.
His two gensets are fueled by propane; they are liquid-mode, temperamental in starting without heat in the coolant and engine block. A liquid mode genset has a vaporizer that uses heat from the coolant to change the propane to vapor. So it’s important the heaters are functioning.
John also used his IR thermometer recently to check for heating of bullets on 3-inch rigid non-flanged line within the transmitter building. He found that the inner conductor on the line to a dummy load had been cut with a tubing cutter. Tubing cutters are convenient but not ideal for rigid line unless you file the cut. The tubing cutter slightly flanges the cut ends inward as it cuts, meaning the bullet will not insert fully.
Fig. 2: Damage to the antenna caused by a ‘marksman.’ This is what John found: the bullet was only making contact in a ring. John assumed correctly that the rest of the plant was plumbed the same way. His non-contact IR thermometer verified that there were problems at each connection, all measured from outside the line.
John scheduled an outage and was able to cut back an inch or so on each end of the rigid line inners. He used a fine-tooth, hand-driven, reciprocating cutter (better known as a hacksaw). He then smoothed the rough edge with a file. After inspecting his bullet couplings, John replaced two bullets that had lost their springiness in the 12 years since installation.
I spoke with John about how he made straight cuts. His answer: Patience, taking the cuts slow. He also uses a trick I learned years ago: Wrap and tape a clean piece of 8-1/2-x-11 copy paper around the rigid line where you want to make the cut. When you line up the two ends of the paper, you have a cut guide. Carefully trace the edge of the paper, all the way around the rigid transmission line, using a fine-point marker like a Sharpie. Remove the paper and cut along your marked line.
It’s important that you rotate the rigid line as you slowly take small bites of the pipe with the hacksaw, until the cut is well established. Saw all the way through, rotating the pipe as you cut. Then remove the burs, as John mentioned, using a file. A Scotch-Brite or similar pad helps make for a clean connection. Just don’t buy pads that are impregnated with soap!
John posed one last question to Workbench readers: How old are the smaller hoses on your gensets?
He reports that several genset mechanics recommend replacing even the good silicone hoses every five years or so. When do we usually discover hose problems? When the genset is needed but unavailable.
Contribute to Workbench. You’ll help your fellow engineers and qualify for SBE recertification credit. Send Workbench tips to [email protected]. Fax to (603) 472-4944.
John Bisset has spent 43 years in the broadcasting industry and is still learning. He is SBE certified and is a past recipient of the SBE’s Educator of the Year Award. He recently joined Elenos USA, an FM transmitter company based in Miami.
