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#21
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Antenna ground planes for composite aircraft
? I never tried this out, but it's just
possible some of that extra gain might get into the coax? Did you ever try this arrangement? Of course, It is called the Willmar Roberts balun against the FCC (Laurel Labs) engineer that invented it. Jim Brian W |
#22
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Antenna ground planes for composite aircraft
RST Engineering wrote:
? I never tried this out, but it's just possible some of that extra gain might get into the coax? Did you ever try this arrangement? Of course, It is called the Willmar Roberts balun against the FCC (Laurel Labs) engineer that invented it. Jim Brian W Well,well! Thanks B |
#23
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Antenna ground planes for composite aircraft
Boy, those are a lot smaller than I thought they had to be. The pie
pans sound like a good idea since they aren't so thin like foil is and easier to keep from damaging. But solder doesn't stick to aluminum, so how to make a good contact that won't come loose to the pie pan? I may just get that antenna kit you sell at RST with that copper foil. I had started to think that you didn't write any ground plane articles in SA, since nothing comes up about that online or in the CD collection. That belly panel on a Glasair is fiber glass with two layers, and a half inch foam core between them. Do the ground planes need to stand off from the inner skin if they are seperated from the lower/outer skin by a half inch? The space between the upper skin of the belly panel and the lower wing skin it covers is less than a quarter inch, so there's no room for the ground plane to stand off. I could mount them back in the tail cone if that is needed. I had thought about installing one of those pre-made di-pole transponder antennas. But to mount it vertically, about the only place I could put it would be on the back side of the spar in the wheel well. And that would put the microwave energy only a half inch away from the fuel cell. Not sure that would be kosher. On a Glasair 3, the entire leading edge of the wing from the spar forward and from tip to tip is all fuel. It makes sense to me that the ferrite beads are needed, as without those, I can't see how the antenna would know where to start and stop. It seems without those, the antenna and the coax would all become the antenna, and be totally out of tune for just about any frequency. Rich On Tue, 22 Dec 2009 10:28:31 -0800, RST Engineering wrote: On Sun, 20 Dec 2009 11:13:46 -0500, rich wrote: I'm installing it on the belly panel. What I'm wondering is how big to make the diameter of the ground plane, and how to make contact with it to the blade type transponder antenna. I would assume it somehow needs to connect to the outer portion of the BNC connector? And what about the GPS antenna, does it need a ground plane? Make both of them out of aluminum pie pans and stand them off from the fiberglass surface so that you don't have any agitated porcupine quills sticking out from the airframe. Transponder diameter about 5.5" diameter; GPS about 3.75" or 11" if the 3.75 is too small to work with. Jim |
#24
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Antenna ground planes for composite aircraft
On Wed, 23 Dec 2009 14:02:11 -0500, rich
wrote: Boy, those are a lot smaller than I thought they had to be. The pie pans sound like a good idea since they aren't so thin like foil is and easier to keep from damaging. But solder doesn't stick to aluminum, so how to make a good contact that won't come loose to the pie pan? I may just get that antenna kit you sell at RST with that copper foil. The transponder and GPS antenna bolt directly to the ground plane. That makes both the mechanical and electrical connections. Copper tape is not being used; the transponder can be the little whip monopole with the BB on the end. The GPS can be any one of a number of commercial units that bolt directly to the ground plane. Copper tape dipoles are used where you need isotropic (whole orange) radiation pattern. Ground plane antennas are where you want hemispherical (half an orange) radiation. Transponder radars are always down. GPS satellites are always up. Unless you fly inverted {;-) I had started to think that you didn't write any ground plane articles in SA, since nothing comes up about that online or in the CD collection. That's true. That belly panel on a Glasair is fiber glass with two layers, and a half inch foam core between them. Do the ground planes need to stand off from the inner skin if they are seperated from the lower/outer skin by a half inch? The space between the upper skin of the belly panel and the lower wing skin it covers is less than a quarter inch, so there's no room for the ground plane to stand off. I could mount them back in the tail cone if that is needed. I do antennas. I don't do mechanicals. That is left to the homebuilder. I had thought about installing one of those pre-made di-pole transponder antennas. But to mount it vertically, about the only place I could put it would be on the back side of the spar in the wheel well. And that would put the microwave energy only a half inch away from the fuel cell. Not sure that would be kosher. On a Glasair 3, the entire leading edge of the wing from the spar forward and from tip to tip is all fuel. Transponder antennas should NOT be dipoles. They should be monopoles on ground planes for the half-orange radiation as described above. It makes sense to me that the ferrite beads are needed, as without those, I can't see how the antenna would know where to start and stop. It seems without those, the antenna and the coax would all become the antenna, and be totally out of tune for just about any frequency. That's not true. The antenna stops where the pigtails converge into coaxial cable. The beads are only there to keep unwanted reflected power from coming back down the outside of the coax cable. Jim Rich On Tue, 22 Dec 2009 10:28:31 -0800, RST Engineering wrote: On Sun, 20 Dec 2009 11:13:46 -0500, rich wrote: I'm installing it on the belly panel. What I'm wondering is how big to make the diameter of the ground plane, and how to make contact with it to the blade type transponder antenna. I would assume it somehow needs to connect to the outer portion of the BNC connector? And what about the GPS antenna, does it need a ground plane? Make both of them out of aluminum pie pans and stand them off from the fiberglass surface so that you don't have any agitated porcupine quills sticking out from the airframe. Transponder diameter about 5.5" diameter; GPS about 3.75" or 11" if the 3.75 is too small to work with. Jim |
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