-----Original Message----- My only antenna currently here at the home QTH is an HF2V vertical which does great for long haul DX on 40 and 80 but in general is not good for local or regional work. I just launched some monofilament over the only high branch in my yard at 50'.
As I only have a single support, I'm looking at some suggestions on constructing a multiband vee wire antenna but have limited materials on hand and even more limited $$ to go out an buy stuff at the moment. Here is what I have in the junk box: 75' of RG213 ~30' of solid conductor commercial ladder line ~800' of 14ga stranded insulated THN wire Assortment of dog-bone style insulators Wide assortment of PVC and nuts/bolts What can I do with the above and the internal tuner in my K1 without going out and buying anything? Ideally, I'd like something that will load well on 80/40/30/20/15 but will settle for 40-15. Anyone have any ideas? ---------------------------------- If you can arrange the wire to come close to your operating position (window, etc.) forget the feed line and use an end-fed wire. Eliminating the feed line eliminates the problem with feeder losses in a multiband antenna. An end-fed inverted V works just as well as a center fed one. Make it as long as possible to keep the feedpoint impedance high. The problem with most end-fed wires is that they are only 1/4 wave long or even shorter. Such antennas are highly-dependent upon a very good ground for good operation. We're talking physical length, no electrical length. Short antennas that have loading devices that make them "look" like they're a half wave long to the RF are still inefficient. You'll want a ground anyway to keep the rig at a low RF potential, even though it's probably not needed for an efficient antenna on most bands. The ideal length for a true ground-independent end fed antenna is a wire a half wave long, but that's a problem with ATU's. They can't handle the very high impedance the antenna will present. So the "trick" is to use as long a wire as you can, greater than 1/2 wave is FB, that will still present an impedance within the range of your ATU on all bands. If you want to work 80, that'll mean something close to or greater than 130 feet. Now add insulated counterpoise wires for each band. They can be run anywhere - along baseboards, stapled to the side of the house, etc., as long as they are insulated from ground and 1/4 wave long for each band. Keep the ends of the counterpoises separate too, at least the last several feed of each wire. Fewer counterpoises will often work, especially on the bands were the antenna is close to 1/2 wave long or greater, but don't fall into the trap of believing that a 1:1 SWR reported by the ATU means the antenna is working efficiently. It only means the rig is feeding power efficiently. What the antenna is doing is something quite different. You want to provide as good an RF ground as you can for each band to ensure the radiator is getting maximum RF current, especially on the lower-frequency bands were the antenna is less than 1/2 wave long. Fifty feet in height will provide excellent signals for close in operations using an end-fed "inverted V" or sloping wire configuration on all the bands below 30 meters and excellent low angle radiation for DX on the higher bands. Even 40 will provide good DX at that height. The ideal height for a horizontal antenna is about 1/2 wavelength above the ground. At 50 feet, expect your horizontal wire to show 4 to 6 dB *GAIN* over your vertical, thanks to the help horizontals get from ground reflections that verticals don't. So it'll have the effect of doubling or quadrupling your effective radiated power. Start with all the wire that fits your yard and counterpoises cut for each band. If your ATU can't find a match on some bands, start shortening the antenna by small steps. Keep in mind that if the higher bands produce a matching problem, you don't need to shorten it by much. For example, shortening the antenna by 10 feet will have a huge effect on 15 meters and virtually no effect on 40 or 80 meters. You can simply fold back the radiator wire on itself and add guy line as needed to shorten it until you find a length that will load on all bands. Folded back wire acts like a "fat" wire to the RF, which flows over the outside of the wire, not through the copper. Once you have a length that works on all bands, you can trim it short and clean up the installation. That would be my first choice. A second choice would be to center feed the wire using the ladder line. You may or may not use a balun, especially if the feed line can be brought to the rig "in the clear" where radiation from the line won't be unduly absorbed by surrounding objects. Just hook one side of the feeder to the hot conductor on the antenna jack and the other to the case. The antenna acts like a combination radiator and counterpoise all built into one. My last choice would be to use the coax. If you do that you *must* have a fairly low SWR on the coax to avoid excessive losses. I'm talking about the coax SWR, not the SWR reported by the ATU. The SWR reported by the ATU is the SWR between the tuner and the K1, not the SWR on the feeder. The easiest way to have a acceptably-low SWR on the coax using a wire antenna is to build parallel center fed dipoles (1/2 wave wires) for each band. Connect each dipole in parallel with the others to the feeder with the feed point as high as possible. Separate the far ends of the dipoles as much as possible to avoid interaction. IF you put up a 40 meter dipole, you don't need another one for 15 since a 40 meter dipole is 3/2 waves at 15 meters and will produce a reasonably low SWR to the feedline on both bands. The other bands will need their own separate wires, however. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. 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