Differential Global Positioning System (DGPS)

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Differential Global Positioning System (DGPS)
DGPS 200Bd.png
Frequencies 283.5 kHz,2.95 MHz
Frequency Range 283.5 kHz - 2.95 MHz
Mode USB
Modulation MSK
ACF —
Emission Designator —
Bandwidth 150 Hz,250 Hz
Location Worldwide
Short Description Differential GPS (DGPS), also known as M823 DGPS and SC-104 DGPS, is a supplementary correction signal used by GPS receivers to increase the accuracy of GPS based positioning.
I/Q Raw Recording —
Audio Sample

Differential GPS (DGPS), also known as M823 DGPS and SC-104 DGPS, is a supplementary correction signal used by GPS receivers to increase the accuracy of GPS based positioning.

DGPS came in two formats, MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) and QPSKQuadrature Phase-Shift Keying (2 bits per symbol). QPSKQuadrature Phase-Shift Keying (2 bits per symbol) was used in the higher frequency bands (1-3 MHzMegaHertz (MHz) 10^6 Hz) but the vast majority of them have stopped broadcasting, while MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) based systems in the 284 kHzKiloHertz (kHz) 10^3 Hz-325 kHzKiloHertz (kHz) 10^3 Hz region are plentiful and expanding.

MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) DGPS uses Minimum Shift Keying (MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.)) and has typical baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. rates of 100 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. or 200 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second.. The 100 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. DGPS signal has about 150 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). of bandwidth and 50 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). shift, and the 200 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. DGPS signals has about 250Hz of bandwidth with 100 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). shift. There are some reports that suggest some DGPS stations run with 300 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. and a shift of 200 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz)..

The QPSKQuadrature Phase-Shift Keying (2 bits per symbol) DGPS used Quadrature Phase Shift Keying (QPSKQuadrature Phase-Shift Keying (2 bits per symbol)) and had ~330 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. with 450 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). of bandwidth.

Note that DGPS has been officially discontinued in the US as of 30 June 2020. See the DGPS Discontinuance page on the US Coast Guard site for more information.

Click Here to Hear DGPS Stations Live at WebSDR Univ. of Twente[edit]

Message Format[edit]

DGPS transmits data in frames. Each frame passes along a certain type of information. These are categorized by Message Types. They can be see here on page 7.

The most common message type transmitted is Type 9, which transmits satellite corrections for a few satellites, often up to three at at time. Although Message Type 1 is the standard type used to send satellite corrections for all satellites in view of the DGPS radio beacon, the Type 9 message is more resistant to noise and allows for faster resync for GPS receivers, so most DGPS beacons transmit Type 9 messages over Type 1.


Samples[edit]

MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) and QPSKQuadrature Phase-Shift Keying (2 bits per symbol)
MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) QPSKQuadrature Phase-Shift Keying (2 bits per symbol)
MSK DGPS.jpg
QPSK DGPS.jpg

MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) 100Bd and 200Bd

MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) 100 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) 200 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second.
DGPS 100bd.png
DGPS 200Bd.png

Additional Samples[edit]

200Bd MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) DGPS

Frequencies[edit]

Most MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) DGPS signals are in the marine radiobeacon 285 kHzKiloHertz (kHz) 10^3 Hz - 315 kHzKiloHertz (kHz) 10^3 Hz band. Some QPSKQuadrature Phase-Shift Keying (2 bits per symbol)-based DGPS signals had been reported a while ago to be in the 1-3 MHzMegaHertz (MHz) 10^6 Hz range, although nowadays only two such signals exist, in Argentina, @ 2570 kHzKiloHertz (kHz) 10^3 Hz and 2950 kHzKiloHertz (kHz) 10^3 Hz. It is unknown if they use MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) or QPSKQuadrature Phase-Shift Keying (2 bits per symbol), but QPSKQuadrature Phase-Shift Keying (2 bits per symbol) is clearly being phased out of DGPS usage.

Decoding Tutorials[edit]

Decoding Software[edit]

Hobby Level Software


Professional Equipment/Software

Video Examples[edit]

Additional Links[edit]

Additional Images[edit]

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