How to use the interactive charts and models

Since I am using limited to 5 Mb web space provided by my ISP, I have tried to design the web site with the idea to pack a lot of information into a small space. Thus I avoid using images (they only show one static view of the data), and instead I use interactive SVG charts and models.

Interactive models

At the top of the antenna model window there may be a line allowing configuration selection. In the example here, one can select from four configs: 0, 2 or 3 NAROD reflectors and no NARODs at all.

Next there is a Selection info line which shows dimensions extracted from the selected elements. Selecting is done by clicking with the mouse, repeated click de-selects, double click in the model area clears the selection. Both lines and line ends can be selected.

If all selected elements have the same X coordinate then x value is displayed in the info. If they have two distinct X values then Δx values is displayed which is the difference of the two. If the selected elements have more then 2 different X values, then no x info is displayed. The same applies to the Y and Z coordinates. At the end is the total length of the selected lines.

In the example shown the two selected wires have the same x=-80.9mm coordinate, the difference in their Z-coordinates is Δz=220.3mm and since the line ends have 4 different y-coordinates no y values are shown. The total length of the two lines is 922.6mm.

Model view elements

The displayed dimension info is in relation to the coordinate system drawn in the center. The coordinate systems also defines the orientation of the antenna by the following convention: +X is towards the transmitter, Y is horizontally broadside and Z is up.

Positioning the cursor over a line shows a balloon with its length, Positioning it over a line end shows its coordinates.

The orange wire in the middle is the source wire. It represents the balun which should be in the middle and its leeds.

The Switch to IN/MM button allows you to change the units in which the info is displayed.

When the Rotation button is active (red) the model can be rotated around by dragging with the mouse. If inactive dragging with the mouse pans the model. With some browsers and if 3-button mouse is used, the middle button rotates and the left button pans.

The rest of the buttons are for selecting different predefined view orientations like Front, Left or Top, for Zooming In/Out, and for resetting the model to its initial view.

Interactive charts

The interactive charts have two scales: on the left side is the Net Gain scale and on the right side is the SWR scale. The Net gain is calculated by subtracting the mismatch loss from the raw antenna gain. Each different model or configuration is drawn with different color shown in the chart legend area at the bottom.

The chart interactivity consists of two things:

picture of mouse hover over a chart

Positioning the mouse cursor over a chart dot will display a balloon with the value of the dot.

picture of switching ON or OFF

Every individual chart curve can be turned ON or OFF by clicking on its legend item.


Q: I spotted what may be an inconsistency in the upper and lower reflector rods. In inches, the top right reflector start is given as (-3 3/8, 0 13/16, 20 11/16), end (-3 3/8, 12 13/16, 20 11/16) The length of the wire is 12 1/16, whereas based on the start and end coordinates it should be just 12 inches.

A: The cause is that when you(the user) subtract the end coordinates you are using 2 rounded values, of which one may be rounded down and the other rounded up. This may result in rounding error that is roughly twice as big as the individual rounding errors on the end coordinates. On the other hand the web site displays lengths that are calculated before the rounding of the coordinates and displayed with a single rounding error.
The rule should be to avoid the use of coordinates to calculate lengths and distances, but rather select two entities and let the webpage calculate the distance/length for you.

Q: How Do I determine the gap between two reflectors? Or how do I find the distance between the reflectors and the active element?.

A: You simply select two line ends and the web page will calculate and display the delta X, delta Y and delta Z in the selection info line.

Q: What are the build tolerances? What will be the performance differences if I build the antenna slightly off specs?

A: JED has done some investigation on the topic here. As a general rule the smaller the dimension the smaller the tolerance. For example the 6mm gap between the active elements and the top hat narods on the GH combo models is fairly critical.

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Copyright 2010 Nikolay Mladenov.
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