Posts Tagged ‘DGPS’

Differential GPS (DGPS)

April 3, 2017

Long-time readers might remember me discussing listening to Non-Directional Beacons (NDBs) on the longwave band (frequencies below the AM broadcast band). A fairly recent addition to the inhabitants of longwave are the Differential GPS stations, which can be found between about 283.5 and 325 KHz. The Wikipedia page with background information is here:

https://en.wikipedia.org/wiki/Differential_GPS

As a digital signal, decoding software is required to be able to DX and log these stations. As luck would have it, Chris Smolinski of Black Cat Systems has written an excellent program called “Amalgamated DGPS” for Windows and Mac. It can be downloaded here:

http://www.blackcatsystems.com/software/dgps_decoding_software_sdr.html

The software can be run using real-time audio from a suitable longwave receiver (or an audio recording). It also functions taking an I/Q recording from a Software Defined Receiver (SDR). This is the way I use the program. I set up my Perseus SDR to record the entire DGPS range (283.5-325) for some period of time. This is an “I/Q” file. The software is then run using the I/Q file as input. It then lists the various DGPS stations it was able to decode.

For each station listed, make note of the “count”. Chris warns that the DGPS error detection protocol is not very robust, and false decodes are common. If the count is just 1, I would say it is fairly likely that a false decode has occurred.