Checking HF Propagation with VOACAP

VOACAP is the current state of 50 years of research into propagation prediction.

It was derived from IONCAP (The Ionospheric Communication Analysis and Prediction Program) which itself has a complicated history. The Voice Of America (VOA) American broadcast network took over its development in 1983 and funded the Naval Research Laboratory to make specific changes. This was completed in 1993 and the system was renamed to VOACAP. The base modeling software is freely available and is the basis of many software products used by ham radio operators.

If you’d like more information on VOACAP’s history and capabilities, see this website:

The good news is that the benefits of all this research and algorithm development is available to anyone who wants to connect to the VOACAP.COM website. This article will lead you through the process of setting up the website to generate a useful display for propagation prediction.

Bear in mind that the propagation predictions are not 100% accurate. They make use of the current solar weather parameters (SSN, SF, A, K), a large amount of historical data, and algorithms that have been improving for 50 years. However, they’re not perfect, although in my experience they’re quite good. Also note that the predictions are calculated once per hour, so the displays are not quite real time.

So let’s see if we can generate a useful propagation display. The website can generate a lot of displays, and one of the challenges is to set it up to display what you’re looking for. I’m going to describe the way to get a world map that shows the probability of establishing a good quality radio path for a given set of parameters, such as band, etc.

Step 1: Preparation

The easy way to specify your location is by using a 6 character grid reference. If you don’t know yours, you can use mine, which will be close enough: EN92IX, or you can look yours up on this website:

Since VOACAP is a website, you’ll need a working Internet connection.

Step 2: Connect to the website

Since the displays are generated on a website, you don’t have to load any software, and the process will work on Windows, Macs, Linux, Raspberry Pi’s, microwaves, and toasters. You might want to open a second copy of these instructions, so that one of them is still readable after you click on the website’s link for map generation, which is:

This should get you to a map of the world that looks like this:


Step 3: Parameter Setup

This gets a little more complicated, but we’ll work through it one parameter at a time.

Find the box at the top left labelled “Select TX QTH” and go to the next box to the right, labelled “or set Grid” Put your grid number here (or mine: EN92IX). Lower case is fine.

In the top right corner is a box for the planned mode, likely CW on your first time into the program. Click the down arrow, and select the mode you’re going to use.

Below that is a box that indicates how much power you’re going to use. Use the down arrow to show the available options, and select the closest one.

Move down to the next box, and click on “Antennas”. A new panel shows up on the left like this:



Select an antenna for both the TX side (you) and the RX side (the rest of the world). Make sure you pick the entry that corresponds to the band you’d be using. I haven’t found that this makes too much difference, and I always pick “1/4 wl vertical” for both sides. Wouldn’t be a bad idea to do some experiments to see if different types make a difference for you.

When you’ve selected antenna types for the right band for both TX and RX, click on the

“Antenna” box on the right side of the screen to get rid of the antenna list panel.

You know what’s coming next... on the right side. click on the “Settings” box below the “Antennas” box which will bring up another new panel on the left side:



Under General Propagation Settings, set the Noise as appropriate. I recommend the “Residential (145)” setting. This can make quite a difference – if you have a lot of noise, select “Industrial (140)” instead, and if you’re in a quiet environment, try “Rural (150)”

Don’t specify a SSN explicitly, but enable Dyn SSN instead. Leave the Method as “Auto”, and the Min. TOA as 3

In the next section, select the band you’ll be working. I leave the UTC and range alone in the belief that they’re not relevant for generating a map of the propagation right now.

I don’t think TX Antenna Analysis applies to our map generation, but I leave it at Dipoles.

In Take-off Angle analysis settings I change from “Year” to “Month” based on something I read somewhere, but I’ve since forgotten where.

Click “settings” on the right to get rid of the Settings panel

I ignore the “Prop Charts” box and the “Prop Wheel” box, and go right for the world map.

At the bottom of the window are 23 buttons with a green background. You may have to scroll down using the scroll bar at the far right of the window to make them visible.


In the middle of the second row is one labelled “REL Map” which stands for Reliability Map.

Click on this button, and try to be patient while you watch a blank white screen for about 10 seconds.

Eventually a map like this appears in the top left corner:



You can make the display bigger with (control – scrollwheel), or (control shift +)

The scale on the right indicates the probability that you can make a good contact with someone in the part of the map with that colour shading, with all the parameters you specified. Red areas have great propagation, blue not so much.

In case you can’t remember what band you selected, the frequency is near the end of the top title line. In this example it says 14.1 Mhz, so it’s 20M.

If you want to go back and look at your parameter settings, or change them, then kill the map display by hitting the X in the top right corner. (If you zoomed in, that will be maintained when you get back to the parameters, so you may want to zoom out again.) Click on the boxes at the top of the right side of the window to select what stuff you want to review or change.

To see how the map was affected when you changed a parameter, just click on the green “REL Map” button at the bottom of the main screen to generate a new map with the current parameters.

If you have questions about this article, or suggestions for improvement, please contact:

         Doug Elliott VA3DAE, This email address is being protected from spambots. You need JavaScript enabled to view it.