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N0LX August 3, 2005
Petlowany Antenna Experiment
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This is my attempt to modify and try out the unusual antenna first described by Bill Petlowany, K6NO, in World Radio Magazine back in March, 1998.
It is essentially a very short dipole with spiral-wound coils at each end. Each coil contains a quarter wavelength of wire at the desired antenna frequency. Bill feeds his as a horizontal, center-fed dipole, and claims excellent results for its size. His 40-meter version is only 12 feet long.
I decided to try it as an endfed vertical, treating it as an electrical halfwave and matching it with a parallel tank circuit consisting of a small toroid and a variable cap out of an old AM radio. I had only a short time to test it out today. With help from Gary, N5ANF, and Paul, KC0MHW, we tested it up in my small front yard just a few feet from the house. Paul was a few miles away listening while Gary and I transmitted. Gary was using a helical-wound vertical and running an FT-817 at 5 watts SSB. I did the same into the my new antenna.
With a 700-foot mountain between us and my signal having to go through my house to reach Paul north of town, He gave both Gary and I an S-2 report. We copied his 100 watts at S-6 to 7. I should mention that Paul was using a horizontal dipole laying across a 6-foot fence at his new house.
We needed to do further testing, but time ran out for the evening.
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LEFT: The whole thing, except the wire, is made from PVC tubing. The antenna is 10 feet long between the coils, and the bottom coil is 4 feet above the ground. The two diagonal lines are small guy ropes.
RIGHT: There is over 34 feet of stranded 22 gauge, insulated wire in each coil. As you can see, I fed the antenna at the outer winding of the bottom coil. The match unit taped to the mast is one I made last month. Again you can see the guy ropes keeping the whole thing vertical in the stiff breeze we had this evening.
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Later in the evening (Ok, 1:00 a.m. local, 0700Z) I went back out and heard several stations on 7.180MHz. One was Larry, W5TZC, at 59+10dB, but he was experiencing a very noisy band and never hear my call. He was talking to Rob, VK4LS, in Australia. I could hear the VK4 at 5x3 with virtually no noise at my location.
Note: I test all my halfwave verticals for proper length by first testing them as a 1/4-wave for half the frequency. I add a radial or two and connect everything to my MFJ antenna analyzer. This antenna, with ~69+ feet of wire plus the 10-foot connecting wire tested resonant at 3.490 MHz. So doubling that gives a 1/2-wave resonance of 6.980MHz. Not too far off from my desired 7.040MHz. I might go back and do some pruning to the coils.
The measured 2:1 bandwidth was around 50 KHz.
I have no idea if this is a decent antenna or just one of those "Ok, I tried it but...." Time, and further testing, will tell.
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