Perhaps it's a good time to take a more in-depth look at how VOACAP Online works. Consider the following a brief user's manual...
Google Maps for coordinate entry
Easy coordinate entry for the Transmitter (TX) and Receiver (RX) was one of the single most important design features at VOACAP Online. The stand-alone PC version of VOACAP does not offer it, and, in fact, not many others do, either. Choosing Google Maps for this purpose lowered the threshold of using VOACAP considerably.
On the initial map, there are two markers - red and blue - placed on the equator line in Africa. The red marker signifies the transmitter's location and the blue marker is the receive location. Perhaps typically, the transmitter is your QTH and the blue one is the DX station.
Need an easy start? Just drag the markers on the map to the desired locations. Zoom the map in/out with the mouse wheel and fine-tune the markers by dragging them to their exact positions. Then press the "Run the prediction" button. That's it!
Great-circle paths: short-path and long-path
There is always a red line between the red and blue markers, showing, by default, the great-cirle path (short-path) between the two locations. A long-path line can be shown when you choose "Long-path" from the pop-up menu by the "Specials" label. Drawing a long-path line on the map was earlier (in Google Maps API v2) not such a trivial thing. At that time, I received enormous help from Sami OH2BFO who programmed the required code. Now, in Google Maps API v3, there was a much simpler way to do it. Thanks Sami for pointing that out!
Distance and bearingOne of the new features is the on-the-fly calculation of the distance between TX and RX, and the bearing from TX to RX in degrees calculated from True North. The details can be found under the map (see image below).
|Image 1. Distance and bearing.|
A closer look at the input valuesThe second most important design feature for VOACAP Online is that, after setting the TX and RX locations, all the input values have been pre-set as appropriately as possible so that you do not necessarily have to adjust them. You can simply press the "Run the prediction" button.
However, there are, of course, many cases where you need more control. Let's take a look at the input values (see image 2 below).
|Image 2. The input pane on the right-hand side of the Google Maps.|
Date & Month, and SSN
The SSN (or, Smoothed Sunspot Number) input field is a new feature which has been requested by many users. Now the user can enter any value between 1 and 200. Use integer values only. Please note that you can simply leave this field empty, and let VOACAP choose the correct SSN values.
At this point, I would like to take a few moments to discuss the pros and cons of this feature. By default, VOACAP Online does internally know the current SSN to be used for all the months of the years available. You can ask how can that be as the sunspot number varies day by day? The simple answer is that VOACAP does not operate on daily SSN figures but smoothed monthly SSN figures which are being predicted for many years ahead and which are re-adjusted at regular intervals.
The predicted SSN figures are based on the Lincoln-McNish smoothing function, and they are maintained by the National Geophysical Data Center (NOAA/NGDC). These are the sunspot numbers used in the database reduction for the worldwide ionospheric maps used in IONCAP and now VOACAP. This is why only these figures should be used with with VOACAP. Read George Lane's discussion on the sunspot numbers for VOACAP use.
However, there have been months in the past where the conditions have been well above the average for a couple of months, and a re-adjustment of SSNs would have been appropriate. Now this power has been given to the user. Just remember that, strictly theoretically speaking, entering a daily SSN value in the SSN field does not generally give you better (or more precise) predictions as VOACAP is not suited to real-time predictions at all. Read more about the theoretical background of VOACAP in my Quick Guide.
This section contains the input parameters for the Transmitter Site (the red marker on the map). The QTH pop-up menu features 481 locations around the world, including all DXCC entities. When you choose a location from this list, its name and the coordinates (latitude and longitude) will automatically be entered in their corresponding fields below. Much care has been taken to find the exact coordinates of even the smallest of the islands! If you happen to find a location with wrong coordinates, drop me a note!
You can also set the coordinates by entering a Maidenhead grid locator in the "Name" field and then pressing the "Loc calc" (or, Locator Calculator) button. The corresponding coordinates will be calculated and shown in their respective fields, and the TX marker will be set to those coordinates on the map.
Please note that while you are dragging any of the markers, the coordinates (latitude and longitude) will be calculated on the fly. When you release the mouse to place the marker at one particular point on the map, its Maidenhead grid locator will be calculated and shown in the "Name" field. This applies to both the TX and RX markers.
There is a huge collection of pre-calculated antennas to choose from. Choose the antenna that is the closest match to your particular antenna. All available antennas are tailor-made for VOACAP Online purposes: they are all omni-directional so there is no need to set the bearing to the RX location.
Then choose the transmitting power and mode. You can also experiment by adding the Sporadic E ionospheric layer to the picture by selecting "Es" from the pop-up menu to the right of the "TX mode" label. The default value is "No Es". However, especially during the summer, choosing "Es" takes the effect of the Es layer into consideration, explaining many of the short-skip contacts on higher HF bands.
Moving on. We already explained earlier the meaning of swapping TX and RX coordinates, and the choice of short-path and long-path great-circle lines on the map.
The last item in the Transmitter Site section is "Current point" with two buttons: "Set Home" and "Unset Home". If you click on the "Set Home" button, a cookie will be stored in your browser which contains the coordinates and the name of the current Transmitter site. This site will be the default start location when you use VOACAP Online next time (instead of the default coordinates of 0,0). If you want to clear the Home coordinates, just press the "Unset Home" button, and all VOACAP-related cookies will be deleted.
The input parameters for the receive site (the blue marker) are much fewer but similar to those found in the Transmitter Site section. You can choose a QTH from the pop-up menu, or enter a Maidenhead grid locator in the "Name" field and press "Loc calc", or move the RX marker with the mouse on the map to the desired location. Then just select the receiving antenna.
Everything is now set so press the "Run the prediction" button. After a few seconds you will see the propagation prediction as a graphic. I will explain in a separate blog entry how to interpret the results and how to access the prediction data as text, too!