Some Hunters Just Can’t Aim Straight
I was speaking with David
Sanford with Texas-based Samco Antennas about RPU antennas recently. Our
discussion migrated to vandalism at stations.
|Fig. 1: A typical GOES satellite yagi from Samco.
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 firstname.lastname@example.org.
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.
* * *
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
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
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.
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.
Fig. 2: Damage to the
antenna caused by a ‘marksman.’
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.
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.
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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.