Eric, K7TV wrote: The HFPACK yahoo group has conducted tests of shortened antennas which seem to indicate that losses in loaded antennas are quite small when the total antenna length is at least half the full length. They compared to reference full-length antennas *at the same height*. As to bandwidth, the automatic tuner in my KX1 easily takes care of that.
-------------------------------------------- Quite true according to the literature and the antenna simulator programs (e.g. EZNEC). Since height of a horizontal radiator has a huge impact on the ground reflection gain, it's not uncommon to find a substantial *increase* in signal strength for short-skip operation by shifting to a lower frequency band where the antenna is only 1/4 wavelength long. Actually, such an antenna does not need to use loading coils. The difference in gain between a center fed radiator 1/2 wavelength long and one only 1/4 wavelength long is less than 0.1 dB. Where more losses usually occur is in the feed line and matching network, wherever it exists. "Loading" the elements or putting some other sort of matching network at the antenna helps provide a low SWR for efficient transmission line operation, but if a low-loss line is used the matching can be done at the rig just as well. In all cases the losses are almost entirely the resistive losses in the conductors, typically the "loading coils" when they're used or in the feed line if a high SWR exists. Remember, we're not talking about d-c resistance, but RF resistance which is typically much, much greater since 'skin effect' forces all the RF current into the surface of the conductor. Small diameter conductors have far more loss at RF than their d-c resistance might suggest. So it's important that largest possible wire in the smallest possible coil be used for loading. That's obviously a big trade-off, of course, one that Buddipole seems to have handled well. Ron AC7AC ______________________________________________________________ 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
