| Right: There is over 34 feet of stranded 22-ga, 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 that evening. |
August 3, 2005
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 end fed 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 that day. With help from Gary, N5ANF, and Paul, KCØMHW, 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.
Later, (Okay, 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 "I tried it but...." Time, and further testing, will tell.
Later, (Okay, 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 "I tried it but...." Time, and further testing, will tell.
| 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. |