DGPS

From HFUnderground

Revision as of 00:00, 7 January 2017

The Differential Global Positioning System (DGPS) transmits correction information that improves the accuracy of the GPS system, from 15 meters to as good as 10 cm. These transmissions are in the 285-325 kHz band, and are interesting DX targets.

A waterfall of the DGPS band

Stations in the United States and Canada typically transmit on 1 kHz channel steps, while those outside of North America can also use 0.5 kHz channels. Transmissions are at 100 or 200 baud, using MFSK. DGPS Data packets contain a 10 bit ID. This ID is not unique, but using a combination of the ID along with the frequency and baud rate allows the specific station to be identified. Data transmissions are continuous, so it is possible to receive many messages per minute from strong stations, as well as the occasional message from more distant or weaker stations. DGPS stations can be used as propagation beacons, observing when messages from the various stations are being received.

Software to decode DGPS includes Amalgamated DGPS which is available for Windows and Macintosh computers. Amalgamated DGPS can decode the entire DGPS band from I/Q recording files made by various popular SDR programs. It can also decode portions of the band from either WAVE audio files, or from live audio via a sound input.

The following is the output from Amalgamated DGPS from a series of I/Q recording files, covering approximately a 24 hour period, as received in Maryland, USA. The list is sorted by the number of received messages (Count) from each station. Many DX stations were received, including from the West Coast and Panama. DGPS stations from Alaska, as well as Europe, have also been received at this location.

Count    ID   ref1 ref2 kHz   Baud City                           Country              Lat      Lon      km     Deg 
3        816  032  033  304.0 100  Aransas Pass, TX               United States        27.842   -97.065  2,269  241 
7        907  304  305  320.0 200  Richmond, BC                   Canada               49.114   -123.183 3,753  302 
23       881  262  263  302.0 100  Point Loma, CA                 United States        32.677   -117.25  3,666  271 
32       886  272  273  287.0 100  Fort Stevens, OR               United States        46.208   -123.96  3,834  297 
46       828  246  247  301.0 100  Angleton, TX                   United States        29.301   -95.484  2,046  241 
62       946  344  345  299.0 200  Rigolet, NL                    Canada               54.25    -58.5    2,127  34  
83       918  310  311  286.0 200  Wiarton, ON                    Canada               44.75    -81.117  656    330 
498      919  308  309  306.0 200  Cardinal, ON                   Canada               44.783   -75.417  579    12  
806      936  332  333  319.0 200  Point Escuminac, NB            Canada               47.075   -64.8    1,278  46  
1037     934  336  337  307.0 200  Fox Island, NS                 Canada               45.361   -61.097  1,442  59  
1513     814  028  029  293.0 200  English Turn, LA               United States        29.886   -89.947  1,608  231 
1676     972  901  902  302.0 200  Miraflores                     Panama               8.993    -79.585  3,425  185 
2364     927  316  317  309.0 200  Lauzon, QC                     Canada               46.821   -71.165  920    29  
2464     937  330  331  298.0 200  Hartlen Point, NS              Canada               44.583   -63.45   1,238  60  
4590     940  338  339  315.0 200  Cape Race, NL                  Canada               46.661   -53.075  2,076  60  
5094     944  342  343  310.0 200  Cape Norman, NL                Canada               51.509   -55.831  2,091  44  
5337     830  100  101  296.0 100  Wisconsin, Point WI            United States        46.708   -92.025  1,444  308 
7622     809  018  019  289.0 100  Cape Canaveral, FL             United States        28.467   -80.554  1,292  196 
7861     836  112  113  292.0 200  Cheboygan, MI                  United States        45.656   -84.475  901    320 
9198     971  903  904  307.0 200  Gatun                          Panama               9.261    -79.937  3,398  186 
10242    839  118  119  322.0 100  Youngstown, NY                 United States        43.239   -78.972  427    338 
15109    869  168  169  290.0 200  Louisville, KY                 United States        38.018   -85.31   745    258 
15927    925  320  321  313.0 200  Moise, QC                      Canada               50.202   -66.119  1,443  32  
16015    865  160  161  320.0 200  Millers Ferry, AL              United States        32.095   -87.397  1,262  231 
16196    864  158  159  317.0 200  St Paul [Alma], MN             United States        44.306   -91.906  1,333  297 
16885    935  334  335  312.0 200  Western Head, NS               Canada               43.993   -64.67   1,124  61  
20834    939  326  327  295.0 200  Partridge Island, NB           Canada               45.239   -66.056  1,085  52  
21937    827  244  245  312.0 200  Tampa, FL                      United States        27.85    -82.543  1,414  203 
28094    831  102  103  298.0 100  Upper Keweenaw, MI             United States        47.233   -88.628  1,257  316 
30161    942  340  341  288.0 200  Cape Ray, NL                   Canada               47.636   -59.241  1,671  52  
33737    778  192  193  292.0 100  Kensington, SC                 United States        33.491   -79.349  723    198 
36717    808  016  017  314.0 200  Card Sound, FL                 United States        25.442   -80.452  1,619  193 
38968    806  012  013  289.0 100  Driver, VA                     United States        36.963   -76.562  307    173 
44091    929  312  313  296.0 200  St Jean Richelieu, QC          Canada               45.324   -73.317  693    24  
44747    926  318  319  300.0 200  Riviere du Loop, QC            Canada               47.762   -69.606  1,073  31  
46205    803  006  007  293.0 100  Moriches, NY                   United States        40.794   -72.756  378    70  
46706    799  044  045  290.0 200  Penobscot, ME                  United States        44.453   -68.776  858    49  
46743    771  196  197  294.0 100  New Bern, NC                   United States        35.181   -77.059  503    181 
58907    863  156  157  311.0 200  Rock Island IL                 United States        42.02    -90.231  1,143  287 
59027    838  116  117  319.0 200  Detroit, MI                    United States        42.306   -83.103  590    301 
73240    777  218  219  304.0 200  Mequon, WI                     United States        43.202   -88.066  1,002  296 
73891    792  136  137  297.0 200  Bobo, MS                       United States        34.125   -90.696  1,367  247 
74725    844  094  095  324.0 200  Hudson Falls, NY               United States        43.272   -73.542  489    35  
74839    870  170  171  309.0 200  Reedy Point, DE                United States        39.569   -75.572  121    97  
75094    772  198  199  306.0 200  Acushnet, MA                   United States        41.749   -70.889  561    64  
78252    804  008  009  286.0 200  Sandy Hook, NJ                 United States        40.475   -74.02   266    70  
78756    847  058  059  301.0 200  Annapolis, MD                  United States        39.018   -76.61   82     158 

References

1. Amalgamated DGPS
2. US Coast Guard DGPS Site
3. Canadian Coast Guard DGPS Site
4. Broadcast Standard for the USCG DGPS Navigation Service - COMDTINST M16577.1
5. Transmission Characteristics of Marine Differential GPS (DGPS) Stations