Ron, I agree on all points. My first antenna was a 40 m dipole with vertical end sections at about 35 ft. Initially I fed it with 300 ribbon cable. Although the antenna was cut roughly for 40m it was probably a bit off. The SWR would have been a minimum of roughly 4:1 but with the vertical ends and moderate height I would guess 6:1 or more. I used a home made balanced tuner and an incandecent bulb to tune for max current. This setup worked, but it worked much better later after I replaced the ribbon cable with home made ladder line. I guess because of this experience I have never again bothered to try 300 ribbon cable in the field. I have used window line in the field, but only for car camping; I consider it too unwieldy for backpacking. For a 1/4 wavelength dipole, in a choice between good high-Q loading coils vs window line, I'll take the loading coils most of the time. However, the very best choice, that I haven't yet tried, may be widely and haphazardly spaced single wires for the feeder.
73, Erik K7TV > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
