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.


  1. Simply great! Thank you so much for this valuable tool.
    73 de LU5DX

  2. Excellent work!The circular diagram is a very nice addition.
    Keep up the good work!
    73,Nick SV1DJG

  3. Muchas felicidades y gracias por tan valioso aporte ...

  4. An awesome user friendly site. I often use it before a RaDAR ops (Rapid Deployment Amateur Radio). The new changes make it even better!
    73 de Eddie ZS6BNE

  5. Good job. I think it would more informative not to use polar coordinates but cartesian. Anyway thank you very much.

  6. Very good, all propagation-parameters in one circle!
    Great Job, Thanks!

  7. Vy Nice tool !
    Beatifully and ergonomically done !

    Vy TNX for it ! The fun is back...

    PP5VX (Bone)

  8. Very good tool.
    But is it possible that you bring an GRID LOCATOR on the world map with on/off Button.?????


  9. Showing the Grid Locator is available while you drag any of the two markers and release the mouse, however not on the map but on one of the text fields. I feel this makes the map more user-friendly.

  10. Great site. Do you know of any prediction tools for delay spread. this is especially relevant to HF data applications. Many thanks!

    1. Hi Paul, unfortunately I don't know of any such tool... :(

  11. Thanks to all of you for providing us this online version of VOACAP.
    I immediately added it to my review of HF propagation analysis & prediction programs.

  12. very good plan to use to find what the best frequency for emergency operations- PY4AAZ SOUTH AMERICA

  13. how to use the Receiver Site, quality: poor, bad, fair, etc.? I do not get it

    thank you

  14. The reception quality means that which level of reception quality you wish to achieve. Then the percentages (the probability) of the VOACAP HF prediction showsyou the probability to achieve that quality you have defined. For example, if you set the Quality to Poor, the probability to achieve that quality is, let's say, 80%. Now, for the same circuit, if you set the Quality to Excellent, the probability may be only 10%.

  15. Could you include probability % for JT65?

    1. Hi Carl, probability percentages are being calculated against a user-set threshold SNR. I have found that assessing reliable threshold values for digital modes is difficult so I have been reluctant to include those in the service.

  16. Very Nice tool !
    Beatifully and ergonomically done !

  17. Superb. Very nicely done. I like the polar coordinate prediction chart -much more convenient than cartesian.
    I note that the predictions are made for 0.1 deg elevation angle. Would it be possible to make the 2 deg elevation angle an option? (I've just been studying the VOACAP manual on this topic, and in my context the 3 deg choice would be more suitable.
    THANKS so much for this. A fantastic tool.

  18. Question; When you refer to " Quality Settings " where can this be found? Excellent program, I use it every day, 73 KC3AZT.

    1. Hi, the Quality setting is not available as such in the ham radio version of VOACAP Online. The Quality input parameter can be found in the Broadcaster version of VOACAP Online, and it refers to the level of the reception quality which is aimed to be reached. The Quality is referred to as an SNR value for AM-modulated broadcasts. 73 Jari OH6BG

    2. Hi Jari, Just discovered your VOACAP online prediction tool today.
      Will start using it and give you feedback soon.
      Thank you.
      73, Lance - VK6DU

  19. Thank you for a wonderful site . always rely on voacap. MW6EYU

  20. Great work, simple intuitive interface!!
    Best Regards

  21. Great work, simple intuitive interface.
    Best Regards
    Jeremy VE3PKC

  22. Great help to the HAMs around the world. Very nice tool. If possible please include option of showing local timings in addition to UTC time.


  23. What do you guys think of using Effective SSN in voacap? Effective SSN I mean not predicted, but reverse calculated from ionosonde measurements.

    1. In theory, the VOACAP engine is created for the use of monthly smoothed sunspot numbers. However, if you wish to experiment, feel free to use Eff SSNs :)

  24. I also just discoved the tool, very exciting. My needs are for short skip (<300 miles) in mountainous territory, NVIS type propagation. The antennas in the list seem high for this type of propagation, 0.1-0.25 wavelength (4-10 meters at 40-meter band). Is it possilble to add a low antenna profile or will one of the existing antennas meet this requirement? I will appreciate any help you might give me.

    David WA7RYV
    Utah, United States

    1. Hi David, pls take a look at the antenna selection for dipoles; there are dipoles which meet your needs.

      73 Jari

  25. This is great, but I notice something odd and have a few questions:

    1. The SSN - the manual says Vocap "knows" the numbers, but, every time I run the prediction without entering a SSN, it shows 44 as the SSN, even when the current number is different (i/e: today it's 38). Further, when I get the SSN from another site and enter it in, I can see the predictions changing - I would think this wouldn't happen if it was looking up the current, correct number on its own.

    2. In light of an apparent glitch in looking up the SSN, I wonder if the program is also looking up the SF, A, and K numbers, if it's actually taking them into consideraion, and if there might be a problem there, too? I see no way to enter these manually - perhaps such a feature would be in order?

    1. Hi Bill, just quick answers:

      1. VOACAP does not use daily sunspot numbers because the VOACAP prediction model, theoretically speaking, is based on monthly smoothed sunspot numbers. This is the reason those SSNs can be built in. See discussion here: http://www.voacap.com/choosingssn.html

      2. Also VOACAP does not consider SF, A or K numbers as it's a statistical model to be applied to the entire month in question.

  26. Very useful. Thanks a lot.
    Luiz PY7BC. Recife. Brazil

  27. Hi
    Awesome program; Only one comment: Every time I open VOACAP, I have to set my Tx & my antenna. Can't we have a method where we can save these settings so that they become my default in my browser? (MacBookPro, Firefox or Chrome) May be a cookie or a config file?
    Mohan VU2DCC

    1. Hi Mohan, and tnx for comments! I adjusted the cookie functionality now so that whenever you click on the "Set Home" button at www.voacap.com/prediction.html, it will remember the TX & RX coordinates as well as TX & RX antenna selections. If you want to clear the cookies (i.e. reset to the "factory settings"), just press the "Unset Home" button. Just make sure that you allow your browser to set the cookies on that page :)

  28. Fantastic tool. Thanks.- CE4RWS

  29. Very great tool, it will be used to overcome the HF communication problems .Thanks