Do You Have a Clear Path?

By David Voit – WB6TOU

How do you determine if you have a clear path for communications? We all know that if we want to have a vhf or uhf signal that lets us talk, we need some elevation for it to work. If you just hold it in your hands, the range is somewhere around 3 to 6 miles on flat land. If you are higher, it goes further. The question is how high do you need to be and that depends on where the receiver is and what is between you and the receiver. A simple search for line of sight propagation gives a lot of information, most of which answers your question with a lot of math about how high your antenna needs to be. You need a site that knows what the ground is doing between your two locations. A useful website that works well without asking you to do the math is: https://www.scadacore.com/tools/rf-path/rf-line-of-sight/.

Move the bubbles down to your location and zoom in. Don’t worry about the graphs that get generated as you find your points of interest. Just zoom into your area and place the bubbles where you want. Here is the path from Lodi to Modesto for ground level. As you can see from the contours, there is dirt in the way and you will not reach Modesto.

Notice on the left and right of the “radio path studyt” graph you can adjust for antenna height. Raise the antenna until both sides are clear of obstacles. The side closest to the obstacle would be raised to clear the close obstacles. Adjust until the path is clear. In this case, the Modesto antenna needs more height than the Lodi antenna. When the path is clear, the line will turn green. The Modesto location would need about 4 meters and the Lodi location just 2 or a bit less.

There is always more to propagation than this, but if you have dirt in the way, it will not work. If there is no dirt, you might need a better antenna or more power. It might be that the propagation is bad for other reasons but at least you can rest assured it is not dirt.