SoftwareAntenna analysis at The DXZone. Theres not much we can do about propagation loss, except to use a software program to predict its effect. And we know that we can increase transmit power, within. Mastless NVIS Antenna. Field day 4. 0 on the cheap. Just in time for Field Day 2. Here is concept antenna you may find worth trying. This answers the call for when you do not have any mast or trees to work with, but still desire 4. As with previous efforts 12, it makes use of ladder line in a folded dipole configuration with one additional reflector wire. The reflector wire improves the signal by about 3 d. B over a single wire antenna. No mast in this context means no structure taller than a person. My criteria means the whole antenna is lower than 6 feet above ground level. The Folded 4. 0m Concept. Nec 4 Antenna Software' title='Nec 4 Antenna Software' />Below is a schematic of the basic idea behind this antenna. Folded 4. 0m NVIS Dipole Concept. Highlights The red lines reveal the parallel ladder line or equivalent wires set up as the driven element. The blue line shows the slightly shorter parasitic wire hovering above the ground to help mitigate some, but not all, ground losses. Ladder Line Element facilitates 5. As with any multi element antenna, parasitic elements load the driver, therefore, lowering feedpoint impedance due to mutual coupling. Such is the case when you add the reflector wire underneath the element in the design above. The classic way to mitigate this is make the driver elements natural impedance much higher than 5. Certainly I will try to answer any questions about the material presented at the sm5bsz site. If you have found errors, please send an Email so I can make corrections. Note Click here to read MOXON antenna performance evaluations provided by several builders. Balun Notes The desired result at the antenna feedpoint is to make. ALE Antennas for Automatic Link Establishment HFLINK is the international resource for ALE Automatic Link Establishment High Frequency Communications, HF Digital. The larger antenna may be built from the smaller one by just adding a boom extension and two elements. With one exception, the. This is much like how the Loop Fed Array Yagi Antennas work. My simulations suggest you can make the ladder line with your favorite wire and simply space it an inch or two apart. The closer the spacing the more supports you will need to ensure the parallel wires do not touch or cross. True ladder line is more convenient for the driver and readily available from local sources. Reflector Wire. As previous efforts suggest, adding one or more reflector wires beneath the driver in any NVIS configuration usually helps the signal by a noticeable amount 123. We make good use of that here, but with just one, more portable, wire. Adding the reflector wire helps byReducing energy lost in heating the ground,Increasing the gain of the low dipole by about 3 d. B,By adjusting its length and height with respect to the driver, we establish a mechanism to adjust the antenna for best gain or best SWR. There is nothing new or novel about reflector wires underneath horizontal dipoles with an example in 1. Fig. 2. 1 2 of Jasiks Antenna Engineering Handbook 4 with later experiments performed by amateurs 123. Our use of NEC merely helps us use this extra wire to refine the whole antenna system rather than simply throwing a wire underneath the driver and hoping for the best. Folded DipoleReflector Element Lengths. The table below is the result of several iterations of NEC using the 4nec. Originally I focused on a design for best SWR and then for best gain. Other antenna configurations, like the full wave loop for example, benefit from this. In the simple dipole I found less than a d. B advantage with optimizing for gain. So the three sets of dimensions below are all focused on best SWR. Frequency. Folded Driver. Reflector. Length. Height. Length. Height. Hz. 68. 1 Ft. 5. 5 Ft. Ft. 0. 7 Ft. 7. 15. Hz. 67. 1 Ft. 5. 5 Ft. Ft. 0. 7 Ft. 7. 25. Hz. 66. 2 Ft. 5. 5 Ft. Ft. 0. 7 Ft. and in metricFrequency. Folded Driver. Reflector. Length. Height. Length. Height. 70. 50 k. Hz. 20. 7. 6 m. 1. Shop for and buy the best Wireless Network Antennas, High Gain Antennas, Antenna Cables at TigerDirect. Hz. 20. 4. 5 m. 1. Hz. 20. 1. 7 m. 1. The above measurements assume bare 1. AWG wire. Different wire size will change the measurements. Insulated wire or window ladder line will require shortening the lengths. Where the best frequency is depends on your materials, but wherever it is it will likely have these SWR and Gain profiles4. Folded NVIS SWR4. Folded NVIS Gain. Shorter Reflector I found several combinations of wire lengths that produce good SWR and acceptable Gain around 3 d. Bi. These include traditional Yagi Uda style wire dimensions where the reflector is a bit longer than the driver 3. However, I frequently find when the reflector is near the ground, having it a bit shorter than the driven element produces a bit more gain. Such is the case in this particular design. Narrow Band. Unfortunately this antenna will not cover the entire band without external tuning. One good solution is to feed this with ladder line from a good antenna matcher. Short of that, you can make this antenna too short and then lengthen it with short ladder line stubs as shown hereFolded Dipole Stubs. Ladder line to dual banana posts and jacks make for a quick and easy way to add these stubs. To maintain perfect balance of currents, the design needs both stubs in the driver. Theoretically a stub in the reflector keeps the antenna at its very best, but to be honest, there is a point where too much is, well, too much. The simulations show the antenna still functions quite well with the reflector as is. Really you can get away without the second stub on the driver just remember to double the length of the one stub. Boba Fett Gauntlet Templates. Your choice. The, of course, you can simply press the tune button on your rig and see what happens. Electric Fence Stakes. The horse and cattle industry provides an ample supply of remarkably sturdy white solid fiberglass poles. Your local farm supply store likely carries at least the four foot long variety. They come in lengths up to eight feet and more. I specified a 5. 5 foot tall dipole in this article with the intention of using 6 foot fiberglass poles pressed into the ground six inches. The electric fence posts have companion metal clips that you can adjust to any height with a simple squeeze and slide. This is absolutely wonderful for antenna fiddling. Here is one sourceFor a high visibility option search for hillman orange reflective rod in your favorite search engine. Lowes has them. They are not designed to hold wire like the fiberglass above, but some thought can make these work. I used them for this Field Day prototypeEnd view of 4. Unfortunately the rods are more narrow than the web site suggests so the clips I purchased from a local farm center were too large to grip. I used green duct tape to hold the clips in place. I will be searching for a better solution. Being non conductive you can use as many as you like. The more posts you use, the less chance of your dipole turning into a Field Day nighttime human trap. Folded Dipole Stakes. In the diagram above you have a squeeze and slide wire clip everywhere a wire crosses a post. Simple, cheap and quick to set up. Good, but not great, NVIS performance. It should come as no surprise this is strictly an NVIS type antenna. I should also point out this antenna, being so close to the ground, is not an ideal configuration for maximum NVIS signal. The following graph compares the 5. Red,the same wire over the additional reflector wire Green,and a 4. V dipole with the apex about 3. Blue. All three plots show the elevation gain profile broadside to the axis of the wires. Gain Comparison of three NVIS Antennas. If you have the facilities to hoist a 4. V or higher configuration by all means do so. It will be better than the 5. Note, however, the additional reflecting wire significantly improves the performance of the reflectorless dipole making it almost as good as the Inverted V. Juniper Junos Training Courses'>Juniper Junos Training Courses. If you are looking for a very simple, but reasonably effective, 4. Bi gain straight up. Experiment. If you build this antenna using the above dimensions, make it a bit long and trim the driver to your target resonance. If all you care about is CW, you can make this cover that with ease by making it longer with a corresponding increase in the reflector.