6m wire antennaAlong with an increase in gain, there will be a change in the radiation pattern.Youre familiar with the doughnut-shaped radiation pattern surrounding a half-wavelength dipolethat pattern breaks up into a multilobed pattern as the length of the antenna is increased.The bottom line is that you may end up with 3 dB gain in some directions with that four-wavelength long wire, but there will also be nulls (where the gain becomes less than that of a dipole) in other directions.With a fixed long-wire antenna, working him.Building a Long Wire for 6 MetersI used the formula 3924/f (where f = frequency in MHz) to determine the overall length of my four-wavelength long wire.
That antenna would fit in my 80-foot space.
I then determined the current-node point by using the formula 234and feeding the antenna that distance from one end.The radiation impedance at that point is about 130 .The resulting SWR, using a 4:1 balun
cable, should be less than 2:1.When you cut your wires, always make them a little longer than the formulas indicate.When you attach the wires to the insulators as shown in Figure 1, wrap the surplus length back on the wires.That way, if you need to lengthen the antenna, you can simply unwrap the extra length.(Two examples: The W2FMI-4:1-HBM200 made by Amidon Associates, PO Box 25867, Santa Ana, CA 92799; tel 714-850-4660; fax 714-850-1163.
The Centaur baluns sold by Amateur Electronic Supply; tel 800-558-0411.) These baluns tend to be bulky and their weight might make your wire sag unacceptably.If this is the case, attach a run of 300- ladder line at the current-node point.The line should be
wavelength at the frequency f.Snake the ladder line back to the 4:1 balun and go from there.Long-Wire Antenna PerformanceIve compared the performance of my 6-meter long wire to my -wavelength vertical during several band openings.The long-wire antenna often performed better! The most noticeable change occurred when I used the long wire for local communication.
The difference was substantial.On some weaker signals switching to the vertical would make the signals disappear! My biggest thrill was working the only double-hop station I heard during the June VHF contestand the rare DX of Sable Island!Multielement Collinear Wire ArrayAs I mentioned earlier, a four-wavelength wire has gain over a dipole of about 3 dB
.The gain isnt higher because the antenna phase.Figure 2 shows how this can be done using a collinear wire arrayFigure 2The multielement collinear array uses stubs to get the RF currents in phase.The stubs in this example are made of -wavelength sections of 450-W ladder line (shorted at the ends).To calculate the lengths of the stubs, use the formula (246/f)V, where f is the center frequency of the antenna and V equals the velocity factor of the ladder line youve .The 4:1 balun is once again attached at the current node point.The collinear is fed the same way as the long-wire antenna but uses -wavelength shorted phasing stubs between the half-wavelength elements.You can make phasing stubs out of common 450- ladder line, but you have to watch the velocity factorconsideration when youre playing with the phases of radio waves.Depending on its velocity factor, the cable you cut to a mechanical
wavelength might be something quite different in an electrical sense.Ive discovered that velocity factors vary between manufacturers of 450- line.Several samples Ive tried had velocity factors frequency.Using the phasing-stub technique, I put up four -wavelength sections with their accompanying matching sections in the same because youre bound to have unequal currents in some of the -wavelength sections, but it is still better than the long wire.The Sterba CurtainThe Sterba curtain antenna is also composed of -wavelength radiating sections and phasing sections.An implementation of this antenna for 10 meters was described in the October 1991 QST (Curtains for You, by Jim Cain, K1TN).The antenna shown in Figure 3, made up of eight -wavelength elements, should have a gain of about 8 dB over a dipole.This is a physically complex in the most-favored directions, other directions will have less gain.Figure 3Construction details for an eight-element 6-meter Sterba curtain.The design frequency is 52 MHz.Note that the phasing section is twisted once, so that the conductors cross.The inner end of an upper element feeds the outer end of a lower one.
If you have a 6-meter antenna tuner with a balanced output, you can feed the curtain with 450-W line between the antenna and the tuner.Otherwise, use a 4:1 balun at the feed point (as in Figures 1 and 2) and you can feed the curtain with 50-W coaxial cable.As the name implies, you hang this antenna vertically, just like a window curtain!a beam and a tower!146 Forest Trail DrLansdale, PA 19446e-mail Gain Antennas for 6 .