# How to plot transmitter coverage area?

As an Extra class licensee, I should probably know this... I am working on a web application for repeater owners. I would like to include an estimated coverage area, provided they have entered all of the necessary information (power, DBi/Dbd, antenna gain, feedline loss, etc).

Is there a formula in which I can use that information to estimate a coverage area?

• Can you share an example of what you're looking for? – Brian K1LI Jun 17 '19 at 17:30
• You say radiation pattern, but do you mean coverage area? – Phil Frost - W8II Jun 17 '19 at 17:34
• Yes, I assume so. By your question I can infer that the two are not the same, which I guess is another point I'm confused on. – Joshua Jun 17 '19 at 21:00
• Radiation pattern is how the antenna's radiant intensity varies by direction, and you just read it from the antenna datasheet or simulation results. Coverage area is a map of where users can likely reach the repeater, taking into account terrain, EIRP, tower height, etc. – Phil Frost - W8II Jun 18 '19 at 15:31
• The radiation pattern published by the antenna manufacturer usually is a theoretical pattern for free space conditions, and does not account for pattern distortions that occur from other nearby structures such as a supporting tower, etc. – Richard Fry Jun 18 '19 at 19:56

## 2 Answers

The Longley-Rice model is a fairly common technique. However it's not a simple formula, and so requires some kind of software to implement. Unfortunately my favorite such tool, CRC CovWeb, has gone defunct.

For a more simplistic prediction, you can try making a simple link budget based on the Friis transmission equation, or if you want to get a little more sophisticated, the two-ray model.

You should additionally consider the radio horizon, and you may perform some simple math to determine how far your antenna can "see" based on an idealized spherical Earth. Or you might use some source of topographic information like heywhatsthat.

Your estimated coverage area is then all the areas that are close enough that free space path loss hasn't attenuated the signal beyond usability, and where terrain isn't in the way.

You will typically find even for modest powers around 5W, terrain and antenna height are most often the limiting factor. Higher powers and antenna gains are typically only useful if the station can be well placed, such as on a large tower, building, or mountaintop.

• Yeah, software is what I do. Which is why I'm looking for details of the model. – Joshua Jul 10 '19 at 15:17
• @Joshua The details of the model won't fit here. Look up the publication. – Phil Frost - W8II Jul 10 '19 at 23:07

There is a web application already: https://www.ve2dbe.com/rmonline_s.asp

73, Brian, ZL1IE

• Right, but they don't publish how it is done, nor do they expose any APIs so it can be used in other applications. – Joshua Jun 19 '19 at 3:47