If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
In article ,
Dennis Mountains wrote: Hi, I'm building a Lancair Legacy (all carbon fiber) and am planning to put copper foil strips on the belly to serve as a ground plane for the belly-mounted com antenna. I'm going to use 1/4" wide copper foil with an adhesive back, attached to the outside of the fuselage and covered with a thin layer of fiberglass (not carbon fiber) to protect the foil. I'll solder it together at the center and attach it somehow to the outside of the BNC connector. I'm planning to make four radials, each 22" long, connected at the center of the antenna and oriented at 90° to each other. I'm using narrow 1/4" copper foil for two reasons: 1) I already own it, left over from my wife's stained glass hobby, and 2) since I'll be sticking it on the outside, the narrow strips are more likely to stay attached to the fuselage when covered with the fiberglass. I think a wider strip is more likely to separate from the fuselage and create a bubble that would be objectionable. Here are my questions: 1. I'm planning to make each of the four radials from three 1/4" wide strips run side-by-side, with 1/8" space between the strips. I hope that this will provide epoxy bonding areas between the strips but still make the antenna think that each radial is a single piece 1" wide. Any idea how the performance of this might compare with a solid 1" wide strip? Any differences will be immaterial. The width of an individual ground-plane 'radiator element' is not particularly significant. Lots of amateur radio stuff uses simple _wire_ for the radials. Works just fine. The only real concern, using 'foil' radials, is to ensure you've got enough cross-sectional area in the radials for the transmitter power level. 2. Is there any benefit to soldering a foil strip across the ends of the three individual strips making up each radial to bond them together at the end opposite the center? NO. There may, in fact, be a _slight_ disadvantage to doing so. At your proposed 1/8" gap, it is, however, _VERY _UNLIKELY_ you'd see any measurable degradation. 3. I'm assuming that 1" wide radials are significantly better than1/4" wide radials; is that true? 'Better?', yes. 'Significantly', no. Using more narrow strips, with the resulting smaller angle between them, is better than a few wide strips. Maybe I'd be just as well off to make each radial out of a single 1/4" wide strip? If you're going to run additional strips, run them as separate radials. 12 strips at 15 degree intervals will provide a closer imitation to a true ground _plane_ than 4 somewhat wider strips will. With any 'non-solid' ground-plane there will be some 'bias' favoring the direction of each radial, vs. 'between the radials'. 4. The Com antenna is a Comant 122, which has a streamlined metal base a couple of inches in diameter. Should the length of the ground plane radials be 22" from the BNC connector at the center of the base or should it have 22" of length extending beyond the base? the 'outside edges' of the radials should be the nominal 22" from the center of the base-plate. Obviously, you can run them just from the outside edge of the base-plate out to the required distance. |
#23
|
|||
|
|||
Hi Robert,
Thanks for your very thorough and thoughtful reply to my questions. You've given me some good ideas to chew on. Thanks, Dennis Johnson |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
rec.aviation.aerobatics FAQ | Dr. Guenther Eichhorn | Aerobatics | 0 | September 1st 04 07:27 AM |
rec.aviation.aerobatics FAQ | Dr. Guenther Eichhorn | Aerobatics | 0 | February 1st 04 07:27 AM |
rec.aviation.aerobatics FAQ | Dr. Guenther Eichhorn | Aerobatics | 0 | January 1st 04 06:27 AM |
rec.aviation.aerobatics FAQ | Dr. Guenther Eichhorn | Aerobatics | 0 | December 1st 03 06:27 AM |
A Good Story | Badwater Bill | Home Built | 15 | September 3rd 03 03:00 PM |