Ham Radio Wire Antenna Calculator
| For ALL ANTENNAS Enter operating frequency in mHz | ||
| For Inverted Vee antennas ONLY, decide what is the approximate angle from horizontal. | ||
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Standard Dipole |
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| Standard Dipole | For best performance over ground, the half-wave dipole should be installed a minimum of 1/2 wavelength above ground. Much higher is alot better. Figure 8 pattern of radiation. | |
| Each Leg Length | ||
Inverted Vee |
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| Inverted Vee | The minimum height for the top feedpoint of the Inverted Vee is determined by the angle or downward slope of the Vee legs. In general the lowest height the legs should be above the ground is 10- 15 feet. Pattern will be between a omni-directional and figure 8 | |
| Inverted Vee, Each leg length | ||
| Minimum Vertical Height | ||
| Horizontal distance between both legs | ||
Quad Loop |
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| Quad Loop | I personally prefer Quad Loops to be used horizontally as high as possible, meaning you need 4 supports, one for each corner. However some prefer to feed them Vertically using only two supports. Vertical Quad loops are most frequently fed in the center of the bottom, horizontal leg. Horizontally at the center of one of the loops. Used Vertically quad loops will exhibit a figure 8 broadside pattern much like a dipole but with better gain. Used Horizontally quad loops are much more omni-directional, with slightly better gain then a dipole overall. | |
| Each Side length | ||
| Feedpoint Distance from Bottom Corner when used Vertically | ||
Delta Loop |
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| Delta Loop | I personally prefer Delta Loops to be used horizontally as high as possible.In general the lowest height the legs should be above the ground is 10- 15 feet. The higher the better your antenna will work. When used horizontally the Delta Loop should be fed at one corner. When used Vertically it can be fed at the bottom horizontal wire center point. It can also be fed at the one of the side wires going up Vertically about 1/4 of the way up, for Vertical polarization. This antenna will have a low take-off angle. | |
| Each Side Length | ||
| Feedpoint Distance from Top when used Vertically | ||
| Feedpoint Distance from Bottom Corner when used Vertically | ||
| Minimum Vertical Height above ground | ||
Half-wave Dipole |
Inverted Vee Dipole |
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Full Wave Loops
Horizontal or Vertical Quad Loop |
Delta Loop Vertically Fed |
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As I always state you must use a Balun with these wire antennas, especially the Loop as the impedance will not always be as you expect. The feedpoint impedance of a full-wave loop in free space is approximately 100-120 ohms with a gain over a dipole from 1 to 1.5 db gain. Installed at practical amateur antenna heights, the range of feedpoint impedance can be from 50-200 ohms depending on your configuration, and choice of feedpoint. Measure with an antenna analyzer and choose the appropriate Balun. Most horizontal loop will come in needing 2.5 to 1 .....to 4 to 1 Baluns. Vertically fed loops either at the bottom center or side will have more variable impedances depending upon your particular installation.
If your loop comes in at around 100 Ohms you have another option to match it (if your allergic to baluns for some reason). You could go old school and match it with a length of 75 ohm coax. How long? Funny you ask.........The formula for matching 75 ohm coax to 50 ohm coax goes like this:
Quarter-wave matching section length in feet = 246 * cable's velocity factor / frequency in MHZ.
If you buy cheap coax (whether its 75 ohm or 50 ohm) the velocity factor is .66 If your smart you buy the better coax which has a velocity factor of between .80 and .84 please check the manufacturers specs to get this number. Basically the higher the velocity factor, the less loss you will have in your coax. Once you feed your loop with your 75 ohm matching cable, connect that to your 50 standard coax going to to rig. be sure to use at least 10 ferrite beads on the 50 ohm section after you connect the matching section of 75 ohm coax. Confused???? BUY A BALUN
