VHF Propagation Map
This map shows actual radio propagation from stations operated near 144 MHz. It uses data gathered by
Automatic Packet Reporting System-Internet Service (APRS-IS) from
packet stations in the
amateur radio service.
The map shows activity that has happened in the past hour. Paths are combined to create color-coded
footprint indicating the distance VHF signals are likely to be traveling. Packet stations typically run
low power into small vertical antennas. Better equipped stations should exceed the the distances these
stations report. The map is updated automatically, typically several times per minute.
The map is created using positions (latitude and longitude) reported by nodes in the packet radio system
and the hops from node to node that the data travels. By correlating the hops with the position of each
end of the hop, the distance can be inferred.
The following is a typical packet that illustrates the process:
STJOHN>APN391,K0SUN-10,AI4GI-3,N5ALC-3*,qAS,KE5NOB:!3916.93N/09454.35WhPHG7330 ...
In this packet, station STJOHN reports its position as 39°16.93' north and 94°54.35' west.
The packet took the path STJOHN, K0SUN-10, AI4GI-3, N5ALC-3. If we previously received and recorded the locations
of each of these stations, then we know the distance it traveled between each of the station pairs:
(STJOHN, K0SUN-10), (K0SUN-10, AI4GI-3), (AI4GI-3, N5ALC-3).
Errors can be present in the data used to create the map. Some stations operate on HF frequencies, which
result in much longer distances than VHF typically supports. Occasionally a packet radio station on a high
altitude balloon or satellite appear. Some stations incorrectly report their position, often by hundreds of miles,
causing local communication to be misrepresented.
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