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About RF Cafe
1996 - 2016
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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I had to check the publication month printed on the cover of the latest Nuts & Volts magazine when I ran across this article last night. It is labeled "August 2015" and not "April 2015," but take a look at the photo below that accompanied an article titled "Build a 50 MHz Dipole out of Crutches" (p25). Author and amateur radio operator Bob Fischer (WB8BEL), aka "The Antenna Sculptor," actually fashioned a working 50 MHz dipole out of a pair of metal-framed crutches. The ones featured in the article were purchased new, but he advises suitable crutches can be bought second-hand for a couple bucks. Admittedly, he says, "I'm certain this novel antenna would never survive high winds or ice loads, but it was not built with permanent installation in mind. I think the best uses for these crutches are teaching antenna resonance, getting attention at Hamfests, and starting conversations about emergency communications at public venues promoting ham radio." It is known that larger diameter antenna elements result in a wider operational bandwidth, so I wonder whether those crutches have a measurably higher bandwidth than a traditional wire element dipole? A simulator model of the radiation pattern with az-el gain would be interesting.
Of course what really caught my attention was the license plate on the host truck. The Internet is full of photos of contraptions that reinforce the stereotype - deserved or not - associated with West Virginia, like the Hillbilly Hot Tub. WV folks, for the record, are some of the best people around. In fact, I have such high regard for them that I married a West Virginian (Melanie is from New Martinsville, and is a WVU alumnus). Note to West Virginians: If you decide to build this antenna, be sure to use metal crutches and not wood, plastic, or fiberglass ;-)
Mr. Fischer, by the way, is a licensed professional engineer, and owner of Fischer Technical Services, located in Huntington, West Virginia. Per his website, "Fischer Technical Services is a small engineering firm that has been providing cost effective plant maintenance and electrical & instrumentation consulting since 1979. If your company has reliability issues, technicians that need to improve their troubleshooting skills or inexperienced engineers, give us a call to discuss how Fischer Technical Services can help. We have an engineer who lives 'where the rubber meets the road.'"
I made a presentation on the development & construction of my crutches antenna at the Huntington, WV Hamfest yesterday.
One of the attendees told me he was going to post a picture of him standing with the antenna to his Facebook page.
I was looking for it this afternoon when I came across your article. Thanks for your kind remarks.
The antenna I built has a <1.2:1 bandwidth of more than 1 MHz.
I was interested in the fact that the dipole needed to be shortened to around 98 inches for 50.5 MHz resonance (As opposed to something in the neighborhood of 108-110 inches.).
I believe that is due to the relatively large "apparent diameter" of the dipole elements. The crutch parallel conductors are roughly 5.5 inches wide. I think that makes the "apparent ratio" of antenna length to conductor diameter on the order of 20/1. Most antennas have ratios on the order of thousands to tens of thousands.
I have worked OK, TX, FL, MO and a lot of New England sitting in my WV driveway with the antenna on the back of the pickup.
Please give my regards to your hillbilly wife.
You have a nice website.
Posted on July 23, 2015