The original poster wants something aesthetically acceptable but performing as well as possible within those limits, whatever they might be. He didn't say it has to be a solution available over the counter. He doesn't say that experimentation is unacceptable. So I suggest that he first construct a temporary solution with a liberal dose of cut-and-try. That allows him to vary size and location parameters that push the envelope to (the limits of) size and xyl acceptability. Then construct a permanent version that looks pretty. What kind of antenna? Start with a vertical with counterpoise, and give it as many variable parameters as possible. Say we start with the tiny vertical dipole consisting of two hamsticks that someone already suggested. Allow physical asymmetry as in making the lower half a shorter length compared to the upper, while retaining the symmetry in electrical length (by means of different loading). Consider making the lower half horizontal. Such L-shaped antennas work quite well (with some directivity), at least on dry land. Consider two of the horizontal counterpoises for symmetry. Take time to experiment and see what works best for you. Make the vertical portion as tall as allowed by the xyl. Of course you need to be able to vary the load inductors for both portions. The counterpoise(s) can be hinged to stay vertical close to the vertical portion when not in use, and floded down like fishing rods to horizontal position for actual use. How to maintain the electrical symmetry? Actually, you don't need to. You let the (L-shaped) dipole become Off-Center-Fed, which gives you another parameter to play with. The popular Buddipole design uses this to help with impedance matching. You should of course use a common mode choke in any case to prevent RF from flowing on the outside of the coax. As you get more off (electrical) center, the need for choking will get more pronounced, until you get really far off center, such that you have essentially an end-fed antenna with just a tiny counterpoise. Such antennas don't need as much common mode choking as do some of the other feed locations, but still need some. As you vary the off-center-ishness, the feed impedance will vary. As already mentioned, this can be used to help matching, but if you go far off center you will need to add a matching device. A popular choice would be a wideband ferrite-cored transformer. As you vary lengths and loading inductances you can measure feed impedance with an analyzer, going for resonance and most pleasing dimensions along with resonance. Then look at the resistive impedance and consider whether a transformer is needed.
73, Erik K7TV ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
