This page provides some tools for the initial layout of a:

Full-Sloper Antenna Half-Sloper Antenna.

The Full-Sloper, or just Sloper, employs a 1/2 λ dipole for the radiating element and is fed at the center of that dipole. Whereas, the Half-Sloper uses a 1/4 λ wire that is fed from the top of the radiating element.


When this page initially loads, the calculator defaults are set for Full-Sloper at 7.1 MHz. The Mast Height is set at 50 feet. The Tower/Mast could be any height, but 50 feet is where a tie point exists. The Upper and Lower Supports initialize to 0.5 feet and 1.0 feet, respectively. The calculator recognizes which input area(s) are populated and which one is not, to calculate the rest of the needed informations. The Upper and Lower Supports are added to the calculated dipole length (1/4 λ × 2) to produce the Slope Length (70' 9-3/16"). These values are then used to calculate the Ground Length and Slope Angle (50' 0-15/16", 45°, respectively).

The input and calculated values are then checked to see if they are reasonable. For this example, all the input and calculated values seem to be reasonable, so all of the length and angle data is listed on the drawing. But, say we also want to see if these data are useful for a Half-Sloper. If you click on the Half-Sloper button, some of the output data will be listed in RED.

In that instance, the calculated values simply do not work. The Slope Length isn't long enough to calculate the Ground Length and Slope Angle can not be calculated, and generates a "Can not calculate B or Slope Angle" error. hence the "NaN" (Not a Number).

Increasing the Lower Support to 15 feet will allow the Ground Length and Slope Angle to be calculated. However, the Slope Angle (86°) makes the antenna almost completely vertical. If that's what you want, you can still use those dimensions, but you will just have a top fed vertical. But if you are trying to experience some of the possible advantages of a Sloper, you might have to increase the Lower Support to 25 feet. This will decrease the Slope Angle to 56°, making the antenna a reasonable Sloper.

Full/Half-Sloper Antenna Calculator

Operation of the calculator is pretty simple. When it first loads, the calculator is set for a Full-Sloper at 7.1 MHz. The Mast Height is 50 feet and Support Lenghts (upper and lower) are set to 0.5 feet and 1 foot, respectively. The calculator will then fill in the data that shows in the upper right of the drawing.

The calculator does not have a calculate button. This is because, calculation is automatic, every time you change an input value and then click outside of the entry area.

Notes and Assumptions

The calculator does not need data in every entry area. If there is a measurement that you are not sure of, or simply don't know, leave the entry area blank or click the "Clear" button.

Initially, a 1/4 λ is calculated from the Center Frequency and the entry area for length is disabled. If you want to specify a specifice length, uncheck the box under the length entry area and enter your own length. The calculations will then, not be dependent on frequency. If you then check the box, the length calculated from the frequency will be re-entered and the input area will be disabled.

Mast Height (A) describes the height from ground, where the Upper Support will be secured. You might have other antennas on the top of the Mast or Tower and would use a point to secure the Sloper, below the other antennas.

The Ground Length (B) describes the point where the Lower Support is tied to ground.

The Slope Length is the sum of the Upper and Lower Support lengths, plus the radiating element 1/2 λ for Full-Sloper, 1/4 λ for Half-Sloper).

The Slope Angle is only calculated to + or - 1 degree. Any further accuracy would be a waste. This is also true when checking for error conditions. The Slope Angle, for error checking purposes, is limited to 30° to 60°. You can use any Slope Angle you like, but outside of that range will be flagged as a possible problem. I haven't found anything specific on the limitations on the Slope Angle. However, at more than 60°, the antenna is just a vertical. At less than 30°, the antenna becomes a horizontal antenna.

The Upper Support is the length of the tie-up rope/cord plus insulator that is used to secure the Feed Point end of the 1/4 λ section, for Half-Slopers, or the upper dipole end, for Full-Slopers.

The Lower Support is the length of the tie-up rope/cord plus insulator that is used to secure the end of the antenna that is near ground.

The calculator will look for different error conditions, depending on the input data. To do this, a Mask is created that defines the calculations required and any error conditions to look for. Overall, creates 256 possibilities. However, many of those possibilities can be lumped together, simplifying the calculations.