Cow tipping
Open-range cattle have one engineer scratching his head when it comes to boresight measurements.
Arnold N Simonsen, Electrical Engineer -- EDN, November 11, 2011
Radar antennas used to guide missiles require rather tight boresighting specifications, usually in the 0.1 degree range or less. Guided anti-aircraft missiles fly at high speeds, so small directional errors can mean missing the target, not a good thing. In the 1970’s our company was producing these radar antennas and missiles for the US government. After being in the field for several years, the antennas would come back to our production facility or a government facility for refurbishment and any necessary repairs. One of the tests done was the boresight specification. At the government test facility the boresight requirement was often out of spec. My boss sent me to the government test site to check out the test failures and find a solution.The government test site was located in one of the United States’ beautiful Western states, so the trip was certain to be interesting, and maybe fun. A typical antenna test site, also called a “test range,” would have a transmitting source antenna mounted on a tower and a receiving test site, where the antenna under test was located a specified distance away, in this case about 1200 feet. At the transmitting site, the tower was mounted on a small trailer also used to house the electronics equipment to generate the test signals transmitted to the antenna under test at the receiving site. At the receiving site was a motorized pedestal on which the antenna to be tested could be mounted to measure antenna pattern features and boresight errors.
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With help from the government engineer assigned to the work, I familiarized myself with the electronics test equipment at the transmit and receive sites. We put an antenna on the test pedestal and ran the required tests. The antenna failed the boresight requirements. We ran another antenna with the same results. Next we checked the optical alignment and, yes, it showed a misalignment of the transmit and receive sites, even though this alignment had been readjusted recently. Typically after boresight test failures, technicians would perform the realignment of the transmit and receive sites. This would correct the problem for some time, but then failures would again show up.
After checking possible causes at the receive site and coming up blank, we went out to the transmit site to investigate. The “test range” was located in beautiful, wide-open country, which was in the middle of “open range.” On open range, cattle are free to roam and graze the area, and there were lots of them around. We looked over everything that could affect the alignment, but found nothing unusual. We again did the realignment, repeated the antenna measurements and found the boresight to be good. Needing some time to let the facts be absorbed, we adjourned for the day, and planned to come back the next day and repeat the measurements.
The next day the boresight readings were again out of spec. Going back out to the transmit site we noticed the cattle rather close to the trailer, but then quickly scurrying away from the trailer and away from us as we approached. We then realized the cattle must be bumping, or leaning on the trailer and moving it on its footings. The footings were under the trailer, out of normal sight, and thus any movement of the trailer could not be seen with casual observation. Even slight movement from a 1000-pound cow would be enough to disturb the 0.1 degree alignment of the transmit site.To fix the problem we had the facilities people put a small fence around the trailer, making it no longer open range. Oh, the winning of the West! The small fence saved the costs of many realignments and test failures, and eliminated many retests. We were happy, the government was happy, and the cattle lost only a little of their open range.
Arnold N Simonsen is a retired electrical engineer, living in Tucson, AZ. After serving in the Air Force as a meteorologist, his work was mostly in RF microwave test equipment design with two aerospace companies.
Talkback
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I seem to remember a similar problem with the cosmic ray detectors for the Pierre Auger observatory in Argentina. They solved the problem by making the structures round rather than square. The cows had no corners to scratch against, so they left them alone.
Gretchen Patti - 2012-14-2 14:36:50 PST -
If the range was as "open" as the cartoon shows, I suspect the cattle were using the trailer to scratch themsleves on, for lack of any convenient trees or fence posts.
Bruce Carsten - 2012-11-2 15:51:32 PST -
From the experience of growing up on a farm full of dairy cattle I found this incident rather humorous!!
Michael Karas - 2012-4-2 11:13:50 PST -
Cows also sweat a lot especially in summer. I've seen tower guy wires with serious corrosion near their anchor points. Evidence of cows scratching themselves are large fur balls coating the guy wires especially at the preforms. Better to fence in those guy anchor points than risk tower collapse! :-)
Ira Wilner - 2012-3-2 13:19:58 PST -
Cattle will destroy almost anything mechanical in their area. They rub, they lick and a few other things. Most of a cow is meat and meat is muscle. Muscle means power and lots of it. Cattle are curious too. They may have scurried away, but had the engineers hung around long enough they would have been subject to this curiosity. Horses are even worse as they will use their front hooves as an investigative tool. Horse lips are as bad as cow tongues in the damage they can do.
TOP - 2012-3-2 12:55:36 PST
