Friday, May 31, 2019

Finding the common moon window times for EME QSOs on VOACAP Online

I am happy to announce that VOACAP Online ( now allows you to determine the time periods when the Moon is visible both at the Transmitter (TX) and the Receiver (RX) sites at the same time, i.e. the common moon window times for EME (Earth-Moon-Earth) QSOs.

You will just place the TX and RX markers on the map at the coordinates of your choice, select the start date from the calendar, and press the green "EME" button underneath the map.

Set the date in the calendar in the bottom-left corner of the map.
Here setting the date to October 18, 2019, the start of the VP6R Pitcairn DXpedition.

After setting the date, press the green "EME" button.

First, the system will calculate the time periods of moon visibility, i.e. moon rise, noon and set times, for both the locations over seven days. Second, it will determine the start and the end of the overlapping time periods in those days, i.e. the times when the Moon is visible in both the QTHs at the same time. And third, within those overlapping periods, more granular calculations take place to determine the elevation over the horizon, the azimuth, and the distance to the Moon at 5-minute intervals. The results will be then displayed side by side for an easy comparison.

A result page with a detailed analysis.
Click image to enlarge.

There are still known problems to reliably handle the cases where the Moon is up all day or is not visible at all during the day. For example, this may happen if you are located far beyond the Arctic or Antarctic Circle.

I hope this will be of service to you while hunting stations via EME. Please send comments and bug reports.