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#1
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Gap Antenna
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#2
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Gap Antenna
Brian Kelly wrote:
Cecil Moore wrote: Denton wrote: I picked up a used one last sprng, set it up about 3 ft off the ground in the back yard...and took it back down within a couple of weeks. Signals were way down compared to my 450 ohm ladder line fed 80 meter doublet on all bands. I had the same experience with a 1/4WL 40m vertical. Now I wish I had run some A/B transmitting tests as well as the A/B receiving tests I thought you did that with N2EY . . ? We did. From Cecil's QTH in Texas to mine here in suburban Philly I could hear no significant difference between the two antennas in A/B tests where I didn't know which antenna was being used (just A versus B). But that's just one data point on one band over one path. which the vertical flunked mainly due to an extremely high noise level. I did some of that sort of A/B testing between an elevated 1/4 wave 40M GP and an 80/75/40M 130 foot end-fed inverted L a number of years ago and the GP did not fare well at all. As it happened there wasn't much of an electrical noise problem in the neighborhood then so QRN one way or the other was not a term in this specific equation. The vertcal leg of the inverted L was spaced about 20 feet from the tower and was base-fed by a remotely controlled L/C tuner out in the back yard, a USN surplus gun director selsyn motor cranked a big rotary inductor which allowed me to QSY from 40 to 80/ 75. But the process ate a minute or two to do which was a pain in the tush during the DX contests I was into. Instantaneous band changing in that game matters. The apex of the L was around 60 feet AGL. The 70 foot "horizontal" run sloped down from the apex to about 35 feet AGL. The L worked quite well on both bands, I could snipe JAs at will with just an SB-200 on either band from here on the east coast when band condx were decent. I decided that I had to put up some kind of 40M antenna so that I could quickly QSY from 80/75 to 40 by simply flipping an antenna selector switch which would get me away from the increasingly annoying "twist the selsyn 30 turns" routine when band swapping. So I built a textbook-classic 40M 1/4 wave GP which had a self-supporting 35 foot +/- radiator. The base was at 35 feet AGL, there were four downward-sloping wire radials. The whole thing perched atop the roof of the abode. SWR over the entire band was essentally unity. Turned out to be a complete waste of time, money and effort. For whatever reason or reasons there wasn't much difference in received signal strength levels beteen the two antennas when I was listening to long-haul DX like JAs and VK/ZLs on my end. But when I called them more times than not they did not come back to me. I spent a couple intense very early morings A/B swapping between the L tuned for 40M and the GP QSOing the DX. In 90% of the cases they "heard me much better" when I was using the L than they did when I used the GP. I took the GP down and good riddance. I'll leave the theoretical howcums of my experince to those of you who are deep into the physics of electromagnetics. For my part another 1/4 wave HF GP just ain't gonna happen here again elevated with radials or ground mounted with gazzilion radials. I think the differences were two: First, the ground plane with four radials wasn't all that hot, and the lossy house was in the near field. The L wire was high-Z and its ground wasn't all that important. Plus the ground was high conductivity moist Aldan soil. Second, the part of the GP with the most current, and therefore doing the most radiating, was the bottom part. I don't know how high the house roof was but it couldn't have been much more than 30-35 feet? But the L wire on 40 meters was a full wave. High current was halfway up the sloping part, and about halfway up the vertical part. So you probably had less ground loss and some serious polarization diversity. End result: they heard you better. . . . half-wave verticals being a whole different ballgame . . I'm thinking about putting the vertical back up as a 1/4WL 30m vertical fed at the base with an SGC-230 that I already have. Such an antenna should work pretty well on 40m-10m, at least for transmitting. Go for it and post your results. Agreed 73 de Jim, N2EY |
#3
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Gap Antenna
In article , "west"
wrote: Anyone have experience with GAP Antennas? On paper they look almost too good to be true, but I know that word of mouth can be more informative. All comments welcomed. West- I've heard third-hand about one Ham Engineer who was having trouble getting a Gap to perform to specs. After discussing it with the company, he decided they misrepresent the antenna and is in the process of filing a class-action suit against them. I couldn't find any information via Google. Fred |
#4
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Gap Antenna
I would like to hear more about that suit. I bought a GAP Titan many
years ago after listening to the hype (lies) from the GAP booth at Dayton. The only thing that was not a lie is the reasonable match it had on all bands, but then so does a dummy load. Mike Fred McKenzie wrote: In article , "west" wrote: Anyone have experience with GAP Antennas? On paper they look almost too good to be true, but I know that word of mouth can be more informative. All comments welcomed. West- I've heard third-hand about one Ham Engineer who was having trouble getting a Gap to perform to specs. After discussing it with the company, he decided they misrepresent the antenna and is in the process of filing a class-action suit against them. I couldn't find any information via Google. Fred |
#5
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Gap Antenna
west wrote: Anyone have experience with GAP Antennas? Here is a link to comments on Gap antennas, found on New Jersey QRP Club's web site : http://www.njqrp.org/data/gap.html I personally have no experience with gap antennas.....Your milage may vary. Rich k2cpe |
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