Sunday, February 4, 2018

VOACAP Point-to-Point QSO Window: know your window of opportunity to work DX!

I am pleased to announce that I have released a new functionality for exploring the windows of QSO-making opportunities at the VOACAP Point-to-Point (P2P) service at This service has been inspired by Risto OH3UU and Cesar PY2YP.

The front page of the VOACAP Point-to-Point prediction service. The new "QSO Window" button is on the right of the page. Click the image to enlarge.

Now, on the Google Map on the VOACAP P2P page, you will see not only two markers (for TX and RX) but also five new red (TX) markers, labelled from A to E. These are the sites of the "competing" locations that are trying to make a QSO with the DX station, too. Now, for you to able to see your chances in relation to the other five, the QSO Window function runs five extra propagation predictions from the five sites to the DX site (RX), and displays the results as interactive charts where you can easily compare the output values to those from your location.

To fully leverage the new functionality, you should set the location of the Transmitter Site (TX) to your QTH, and the location of the Receiver Site (RX) to that of the DX. The five red markers are additional Transmitter sites, too, and their default locations have been chosen to reflect perhaps a typical set-up:

  • A = West Coast USA
  • B = East Coast USA
  • C = South Europe (Italy)
  • D = East Europe/Russia West
  • E = Japan

The user can freely set these markers to his/her liking on the map.

When you have set up the TX and RX locations, the five extra markers, and other input values, then press the "QSO Window" button. A new window will appear with results. If no results will appear, just refresh the result page. It can be that there are too many users at that particular moment.

Please note that the five "competing" stations will use the same input values you have set to the Transmitter (TX): the same antennas per band, the same power, the same mode, path, etc.

Finding the best QSO Windows by band

The results will be displayed band-by-band as interactive graphs for the following VOACAP output parameters:

  • Median Power Power (SDBW, displayed on a S-meter scale)
  • Reliability (REL)
  • Median Signal-to-Noise Radio (SNR)

The header of the result page: Short/Long Path, and distance and bearing. Click to enlarge.
The header of the result page: The coordinates of the five TX stations (markers A to E). Click to enlarge.
On each graph, each station (TX and stations A to E) has a color of its own, and the legend below the graph shows which color belongs to which stations. As you have set your own QTH to the Transmitter (TX), your color is that of the TX station (typically blue).

The result graphs for comparing the results -- and finding the best QSO windows! Click to enlarge.

All the graphs are interactive, which means that you can hover the mouse over the graph and see the results instantly by station. At the bottom of the graph, the UTC hour will be highlighted as you compare the result values with each other. If you feel the graph is too messy and the number of the lines should be reduced, just click on the color of the line in the legend. Adn if you want to see the line again, just click the legend once more.

This is an example circuit from Finland to Rotuma in February 2018. The SNR of the TX site (Finland) peaks at 9 UTC, with the predicted SNR value of 28 (dB/Hz). So, just about readable! However, as we can see, there can be tremendous QSO walls from sites D (East Europe/Russia West), C (Southern Europe/Italy) and E (Japan).

In the Signal-to-Noise (SNR) section, all the graphs have a red dotted horizontal running through the graph. The line has been drawn at 24 dB/Hz, which is to indicate where the threshold for CW copy in terms of SNR has been set.


  1. Where are official SSN numbers for use in voacap published? Hamcap which uses same prediction engine gives slightly different value for 2020.11 than FTP link provided in seem does not be working.

  2. VOACAP Online uses the SSN numbers from . I am not using them as such, though. The difference maybe there.

  3. Pardon my annoyance, by default (SSN=-1) takes SSN value=9, while link above gives SSN 2020.11=13

  4. That is correct. I am not using the values as such. There is a difference. However, you can set the SSN to 13 manually if you wish.