Tuesday, July 23, 2013

VOACAP Online Next Generation: User Manual

VOACAP Online has got a face-lift, and, on this occasion, I decided to write a brief User Manual for the service.

URL: http://www.voacap.com/prediction.html


VOACAP Online is a web-based HF propagation prediction service which uses VOACAP (Voice of America Coverage Analysis Program) as its calculation engine.

Unlike the previous version, this new service requires that SVG (Scalable Vector Graphics) is supported in your web browser. The latest versions of Microsoft Internet Explorer, Mozilla Firefox, and Google Chrome are known to work. The earlier versions may not be supported. If you encounter problems with the page, please try first to upgrade your browser to the latest version available. If you think you have found a bug, please report it to jpe@voacap.com.

The web interface is divided into three parts:
  1. a Google Map for setting the transmitter (TX) and receiver (RX) site coordinates. The easiest way to set the coordinates is to drag the markers to appropriate locations on the map. Under the map, the distance from TX to RX is given in kilometers and miles, and the bearing in degrees from True North. If you need to zoom in or zoom out the map for better details, just scroll the mouse wheel up and down.
  2. a circular prediction chart which is divided into 24 hours and which shows all the amateur radio bands from 10 meters (28 MHz) to 80 meters (3.5 MHz). The prediction shows the probability for a QSO between the TX and RX site, illustrated as colors. The white and blue colors indicate poor probability whereas orange and red indicate good probability. The exact probabilities can be seen by hovering the mouse over the chart. The prediction details (UTC hour, band and probability (%)) will be shown in the centre of the chart.
  3. the input values for the prediction can be set in the area below the Google Map and the prediction chart. There are three sections:
    1. Date
    2. Transmitter Site, and
    3. Receiver Site.
The new circular 24-hour prediction chart, which is updated as soon as any of the input values (coordinates, power, antenna, year, month, etc.) changes.

The Date Section

Old info: In the Date section you can choose the year (currently 2013, 2014, 2015) and month. In this section, it is also possible to set a specific SSN or sunspot number to be used for calculations. Note that VOACAP Online knows about the current sunspot numbers so it is advisable not to set any value to the SSN field unless you are conducting some experiments. After you have entered a value in the SSN field, press the TAB key (instead of the ENTER key) to run a prediction which is shown in the prediction chart.

EDIT, 4 June 2016: The whole concept of setting the date in VOACAP Online has been changed after I implemented the grayline terminator functionality in the service, and this has been quite awhile ago. Also, setting the SSN has been moved to a section of its own, called "Propagation Params". Let me remind you, however, that when I say that VOACAP Online knows what SSN to use, I refer to monthly smoothed sunspot numbers, not any daily value. If you wish to experiment with daily SSN values, you will need to enter them manually.

The new way of setting a date and time was necessary after I found a code which allowed me to show the grayline terminator on the map. Earlier, I was also showing the grayline but it was always fixed to the current time and day -- the user was not able to set it to a specific time and day in order to see how the grayline terminator looked like on a particular point of time. I felt that the grayline map could be used as a way of predicting signal enhancements on the low bands but a new way of setting the time and day was badly needed.

And this was the reason I chose to use a pop-up calendar for this particular purpose. In addition, any month the user would select for the grayline would also be used as input for all propagation predictions.

The pop-up calendar is located just below the Google Map, and looks like this:

Select a day number in the pop-up calendar, and press the Set button.
Press the Reset button to return to the current time and date.

To set a date, click on the calendar icon on the right of the date field. It will prompt a calendar where the user can browse the months (and years) backward and forward, by pressing the arrow icons. You select a month by clicking on any day number in that particular month. Please note that you must select a day!

The selected month will also be used for propagation prediction calculations, and the selected day (and the time set by the user) will be used for drawing the grayline terminator over the Google Map. Please note that the selected day will not be used for propagation prediction calculations as VOACAP will not calculate any daily predictions.

When you have selected a month and a day, and have set the time correctly for your purposes, then press the Set button. This will finally use all the parameters set. To return to the current month, day and time, press the Reset button.

The Transmitter Site

In the Transmitter Site section you can, besides dragging the red marker to the appropriate location on the map,  choose the location from a list of DXCC countries. Basically, you use the Name field for entering a label for the TX site. But you can also enter the Maidenhead grid locator in the Name field, and press the "Loc calc" key: the corresponding coordinates will automatically be calculated from the grid locator and entered in the Latitude and Longitude fields. The latitude and longitude values can also be entered manually. When you do that, please press the TAB key to run the prediction.

In this section, you can also select the most appropriate antenna for the TX site. At the moment, only one antenna can be chosen for all amateur bands. The default is a dipole at the height of 10 meters (33 ft) above the ground. All TX and RX antennas are artificial in the sense that they are omnidirectional, which allows the user to see all possible openings to all parts of the world. In dipole-type of antennas, the height of the antenna is related to the elevation angle and the number of elements to the gain. When you choose an antenna, you should think about the elevation angles and gain, rather than the physical structure of the antenna.

In the TX power, you can select powers from 1 watt to 1500 watts at the given steps. 100 W is the default selection. Some line loss is assumed so that the actual power used in the calculation is 80% of the chosen power. In the TX mode, you can choose from CW, SSB and AM. CW is the default selection.

There are also two special settings: the setting of Es (sporadic E) layer to on or off. The default setting is OFF (No Es). This can be set to ON (Es) during the summer time when the effects of the sporadic E layer are strongest. The second is the setting of Short-Path or Long-Path. Short-path means the shortest distance between the TX and RX, and this so-called great circle path is visualized with a red line on the Google Map. If you set this to Long-path, you will go from TX to RX in the opposite way: the longest great-circle path.

Last but not the least, there are three buttons:
  • Swap TX-RX,
  • Set Home, and
  • Unset Home.
If you click on the Swap TX-RX button, the TX and RX locations will be swapped: the current TX location becomes the RX location, and the RX location becomes the TX location. You can accomplish the same effect by double-clicking the red (TX) or blue (RX) marker on the map. In this way, you will see that the circuits are not always 100% reciprocal. In VOACAP calculations, this is mostly due to the different level of noise power in the RX site.

Old Info: By clicking on the Set Home button the TX Name, Latitude and Longitude will be stored in a cookie, to be used by your browser automatically when you visit VOACAP Online next time. If you press the Unset Home button, the cookie will be deleted from your browser.

EDIT, 4 June 2016: Now, not only the TX Name, Latitude and Longitude information is stored in a cookie, but also the RX Name, RX Latitude and Longitude as well as the TX and RX antenna selections are stored, when the Set Home button is pressed. And when you press the Unset Home button, the cookie will be destroyed. Remember to allow your browser to set the cookie on this page.

The Receiver Site

In this section, the input options are similar to those of the Transmitter Site. The RX location can be selected from the pre-defined DXCC list, or coordinates can be entered manually in the Latitude and Longitude fields. If you enter the values manually, please remember to press the TAB key.

The Name field is used to give a label for this site, or alternatively you can enter a Maidenhead grid locator in this field and press the "Loc calc" button, and the latitude and longitude values will be calculated automatically.

Also the receiving antenna selection is exactly the same as for the Transmitter Site.

Below the Receiver Site section there is the "Run prediction!" button. This will calculate the detailed propagation prediction graph for the entire frequency range from 2 MHz to 30 MHz, and show the day/night times for each location. This was the only way of getting the prediction in the previous version of VOACAP Online.

That's it ... in a nutshell! If you have questions, please don't hesitate to drop me a note.

Thursday, May 16, 2013

VOACAP Online upgraded!

The online point-to-point HF (3-30 MHz) propagation prediction service VOACAP Online was upgraded this week. The Google Maps portion of the site is now using the API version 3, and some new functionality was added, too.

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 bearing

One 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.

And if you would like to swap the TX and RX locations, there are two ways to do it. The easiest way is to double-click on either of the markers. The bearing value will be re-calculated at once. You can also click on the "Swap TX-RX" button by the "Specials" label.

A closer look at the input values

The 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.
There are three sections in the input pane: Date, Transmitter Site, and Receiver Site.

Date & Month, and SSN
The year and month values are automatically selected (by the Javascript code on the page) to reflect the current year and the current month. If not or if you would like to change them, just choose the desired year and month from the pop-up menus. At the moment, the selection of years goes to the year 2015. I regularly (manually) update the contents of this pop-up menu.

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.

Transmitter Site
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.

Receiver Site
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!