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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Donations accepted
$5 USD
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$25 USD
If you appreciate this service and wish to donate, funds received will be used to add a remote tuner to the HF horizontal loop at the local public high school station. Payments are not required to use this service, nor do they imply an added benefit such as a higher grade of service or continuation of the service. Sufficient funds have been received to repair the vhf and uhf antennas at the high school. Thank you!

OpenLayers map display
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APRS Footprint
	Show live footprint
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Pan and Zoom
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Interactions
	Pan and zoom resets view bounds and reloads
	Hover to select footprint
	Popup callsigns of APRS stations
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