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Antenna ground plane and coax grounding
"Bill French" wrote in message ... I have been having some transmission problems in my rag wing airplane - not getting the transmission distance I should be getting. On the way to the radio shop for a SWR check I could send and recieve at 2000' AGL for a distance of 40 miles behind me. Report of 5 square. Returning over the same course I was at the same altitude but could only get a 4 x4 at 30 miles. SWR check showed between 2.5 and 2.9 - acceptable but just barely. Changed antenna and had the same reading. My ground plane is an aluminum plate about 12" by 8" and the antenna is mounted at the extreme forward end - that is toward the cockpit. This probably accounts for the differences in for and aft transmissions. I've read that the ground plane or reinforcement plate that the antenna is mounted should be grounded. Is it sufficient to have it grounded through the coax shield and then have the shield grounded to the airframe at the radio or should the plate be grounded at the antenna? Would I be better off trying to increase the size of this plate with aluminum foil or something similar? Any help greatly appreciated. Bill French The grounding should ideally be at both ends of the coax. Make sure that it is a good solid ground to give the best results. When grounded to the airframe, the airframe also becomes part of the ground plane , so your signal will radiate best to the rear. if possible, try moving the antenna toward the center of the fuselage. |
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"JLB" wrote in message ... What frequency are you assuming? 22" is a quarter wavelength at 134 Mhz, which is a bit too high for the aviation band. Can you say velocity factor? |
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"JLB" wrote in message ... Last time I checked the velocity factor of air is pretty close to 1.00000000. Yeah, but the velocity factor of the material the ground counterpoise is being made out of is the issue. |
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