VHF propagation conditions through APRS

With the upcoming VHF contest, propagation is important. I found a tool that is new to me, but familiar to many others. It uses APRS gateways to determine how far two-metre signals are travelling at the current time. It's completely in real time, so you can see the conditions shift.

The site is aprs.mountainlake.k12.mn.us and it uses the Google Maps API and raw packet data from the APRS network to graphically display where APRS digipeaters and transmitting gateways are reaching. This gives you a rough idea of the current VHF band conditions.

The map shows a signal path as a "cloud" over the area, which is colour-coded by distance reached. If you click on the "cloud", you will see the stations in contact with a particular gateway. These clouds often overlap. You can see an example of both phenomena below.

When a "cloud is clicked, you see the stations reached

There are a few things to bear in mind. First, these are packet signals, which are more readable in noise than voice. Second, this is FM. SSB and CW will be readable over much longer distances than the "clouds" indicate. Third, not all APRS gateways are created equal. Some are on towers, for example, while others are home base stations. And gateways aren't evenly distributed.

If you click on the station ID attached to a "cloud", you can see the data for that gateway, such as the individual stations contacted and their distance from the gateway.

Overlapping clouds don't mean that there's continuous propagation throughout. But a cluster of clouds is an indication of improved conditions in general in that area. The example above shows W0YC at the U of M being heard 75 miles to the south.

Providing propagation data is a benefit of having a home APRS gateway, as you'll always know conditions at your location. APRS data is nearly constant, much like a propagation beacon.

Frequently, there are orange and even red "clouds" in various parts of the country, with signals being heard several hundred miles away. If you are in those places, it would be an excellent time to try your hand at two-metre FM simplex or sideband.