This product is no longer available.
Note: The DGPS kit requires the use of the Oncore VP GPS engine. Motorola discontinued the Oncore VP in August of 1999. TAPR is no longer able to supply Oncore VP units for this kit. We suggest you contact Synergy Syetsm (Gina) for any Oncore VP units they might have available. While new units are no longer available, surplus and refurbished units can be found.
Differential GPS Reference Station Interface on left
Example of Oncore attached to DGPS Interface on right
Description
The Differential GPS (DGPS) Reference Station Interface Board connects to a Motorola Oncore VP OEM GPS receiver to create a low cost 8-channel DGPS Reference Station.; The Reference Station provides Pseudo-range Differential GPS corrections that conform to the RTCM SC-104 Type 1 message format. Corrections can be transmitted via data link to remote users.; Possible data links are radio modems, terminal node controllers (TNC), or telephone modems.; Remote users receive the corrections and apply them to their DGPS ready receiver to calculate a DGPS solution.For example, a Radio Amateur installation would use a 2-meter transmitter and TNC.; Using the 2-meter frequency of 144.39 MHz, the new APRS frequency, APRS trackers can take advantage of DGPS accuracies (see performance below).; No special equipment is needed by remote users.; Corrections are received using a 2-meter (mobile or handheld) receiver and TNC.; The output of the TNC is connected to a DGPS "ready" receiver.
Commercial users can connect the DGPS Interface board to commercial data radios.; The responsibility of using the correct frequencies is up to the user.
Possible uses include:
- Search and Rescue
- APRS Trackers
- Parades
- Marathons
- Balloon Tracking
- Research and Development
- Vehicle Location in a metropolitan areas
- Anything that requires increased GPS accuracy
Setup of the DGPS Reference Station is easy.; The output baud rate and the Station ID is selectable via jumpers.; The latitude, longitude, and altitude of the reference location and the rate at which corrections will be transmitted are programmed via software commands.; The Reference Station then operates without any further intervention.
Download DGPS Assembly Manual (pdf format, 498K)
Features
- Operates with the Motorola Oncore VP 8-Channel GPS Receiver
- Reference Station is Compatible with DGPS "ready" receivers that accept RTCM SC-104 Type 1 Messages
- Easy setup and operation, suitable for portable operations
- Programming via RS-232 serial port
- Outputs RTCM SC-104 Type 1 Message with a selectable RS-232 output baud rate: 1200, 2400, 4800, and 9600 baud
- Selectable Station ID: 0 - 1023
- Power Requirements: 7 - 30 VDC
- Power Consumption: 235 milliamps typical with Oncore VP with Active antenna
- Lithium; Battery Backup Option for Oncore VPs without battery backup
Performance
Using Stan Huntting's, KW7KW, SA Watch program, you can see the difference DGPS has over civil GPS.; The following GPS receivers were held stationary and received differential corrections from the TAPR DGPS Reference Station. Differential corrections were transmitted on 145.79 MHz (the previous APRS frequency) and two plots were made for each receiver.; The first plot without differential corrections and the second with.
Zero Baseline Tests
The Zero Baseline test connects the TAPR DGPS Reference Station to a remote GPS receiver under test using the same antenna.; Both receivers connect to the same antenna via a 2-way DC isolated L-band power splitter.
DGPS References
- About DGPS - a tutorial
by Dr. Thomas A. Clark, W3IWI, Reprinted from Packet Status Register Summer 1997 - Issue #67
DGPS Links
NOTE: These have all gone dead. If you know or find out where they've moved, please let us know.- Sam Wormley's Differential Global Positioning System (DGPS) Information
- US Coast Guard Navigation Center
- Differential GPS Information
Performance of the TAPR Differential GPS Reference Station using a Garmin GPS-20
Garmin GPS-20 Without Differential Corrections
The display below shows the Garmin GPS-20 collected non-differential GPS
positions for approximatelly 2 hours. SA Watch calculated the 95th
percentile as 59 meters. The scale of the outer ring is 150 meters.
Garmin GPS-20 With Differential Corrections
The display below shows the Garmin GPS-20 collected differential GPS positions
for approximatelly 2 hours. The differential corrections were transmitted
every 15 seconds. SA Watch calculated the 95th percentile as 15 meters.
The scale of the outer ring is 150 meters.
Performance of the TAPR Differential GPS Reference Station using a Garmin GPS-45
Garmin GPS-45 Without Differential Corrections
The display below shows the Garmin GPS-45 collected non-differential GPS
positions for approximatelly 2.3 hours. SA Watch calculated the 95th
percentile as 64 meters. The scale of the outer ring is 150 meters.
Garmin GPS-45 With Differential Corrections
The display below shows the Garmin GPS-45 collected differential GPS positions
for 5 hours. The differential corrections were transmitted every
10 seconds. SA Watch calculated the 95th percentile as 16 meters.
The scale of the outer ring is 150 meters.
Performance of the TAPR Differential GPS Reference Station using a Motorola Oncore VP
Motorola Oncore VP Without Differential Corrections
The display below shows the Oncore VP collected non-differential GPS positions
for approximatelly 9.5 hours. SA Watch calculated the 95th percentile
as 58 meters.
Motorola Oncore VP With Differential Corrections
The display below shows the Oncore VP collected differential GPS positions
for approximatelly 5 hours. The differential corrections were transmitted
every 10 seconds. SA Watch calculated the 95th percentile as 11 meters.
The following plots the scale was changed. The outer ring is 15 meters
Motorola Oncore VP Without Differential Corrections
The display below shows the Oncore VP collected non-differential GPS positions
for approximatelly 2 hours. SA Watch calculated the 95th percentile
as 78 meters.
Motorola Oncore VP With Differential Corrections
The display below shows the Oncore VP collected differential GPS positions
for approximatelly 2 hours. The differential corrections were transmitted
every 15 seconds. SA Watch calculated the 95th percentile as 11 meters.
Zero Baseline Test
The Zero Baseline test connects the TAPR DGPS Reference Station to a remote GPS receiver under test using the same antenna. Both receivers connect to the same antenna via a 2-way DC isolated L-band power splitter. The plots below were made using a Oncore VP as the remote DGPS receiver. The reference coordinates were 30:46:58.965N 81:40:30.830W. The RTCM output of the Reference Station was connected directly to the Oncore VP (i.e., no radio link).Zero Baseline test were also done with the following GPS receivers as remote receivers:
The below plot positions were collected for 10 hours 17 minutes. The RTCM output of the Reference Station was at a rate of one message every 1 second. SAWatch calculated the 95th percentile at 3 meters. The scale of the outer ring is 15 meters.
The below plot positions were collected for 11 hours. The RTCM output of the Reference Station was at a rate of one message every 5 seconds. SAWatch calculated the 95th percentile at 4 meters. The scale of the outer ring is 15 meters.
SA Watch Statistics (edited)
First sample: 01:55:31 10.Jan.1998 Last sample: 12:26:21 10.Jan.1998 UTC Elapsed time: 0:10:30:50 Logging time: 0:10:30:50 for 18,927 records Logging interval: 100%@2sec Sample interval is all samples yielding 18,926 samples
Element Minimum Maximum Mean St Dev Latitude 30:46:58.7460N 30:46:59.1540N 30:46:58.9604N 0:00:00.04935 Longitude 81:40:31.1280W 81:40:30.5880W 81:40:30.8312W 0:00:00.05895 Elevation -8.500m 27.800m 12.781m 3.6097m UTM Easting 17 0435384.242 17 0435398.671 17 0435392.171 1.5660m UTM Northing R 3405746.518 R 3405758.991 R 3405753.070 1.5261m 2D Position 2.1866m 3D Position 4.2203m HDOP 0.9 4.5 1.54 SVs Tracking 5 8 6.84
The below plot positions were collected for 11 hours 19 minutes. The RTCM output of the Reference Station was at a rate of one message every 10 seconds. SAWatch calculated the 95th percentile at 5 meters. The scale of the outer ring is 15 meters.
SA Watch Statistics (edited)
First sample: 12:41:01 10.Jan.1998 Last sample: 23:59:57 10.Jan.1998 UTC Elapsed time: 0:11:18:56 Logging time: 0:11:18:56 for 20,370 records Logging interval: 100%@2sec Sample interval is all samples yielding 20,369 samples
Element Minimum Maximum Mean St Dev Latitude 30:46:58.632N 30:46:59.292N 30:46:58.951N 0:00:00.0656 Longitude 81:40:31.320W 81:40:30.540W 81:40:30.829W 0:00:00.0642 Elevation -22.20m 32.30m 11.49m 4.631m UTM Easting 17 0435379.12 17 0435399.97 17 0435392.23 1.705m UTM Northing R 3405743.04 R 3405763.23 R 3405752.77 2.029m 2D Position 2.650m 3D Position 5.335m HDOP 1.0 3.4 1.40 SVs Tracking 4 8 6.77
The below plot positions were collected for 10 hours 35 minutes. The RTCM output of the Reference Station was at a rate of one message every 15 seconds. SAWatch calculated the 95th percentile at 8 meters. The scale of the outer ring is 15 meters.
SA Watch Statistics (edited)
First sample: 04:06:33 11.Jan.1998 Last sample: 14:41:23 11.Jan.1998 UTC Elapsed time: 0:10:34:50 Logging time: 0:10:34:50 for 19,047 records Logging interval: 100%@2sec Sample interval is all samples yielding 19,046 samples
Element Minimum Maximum Mean St Dev Latitude 30:46:58.566N 30:46:59.520N 30:46:58.967N 0:00:00.1037 Longitude 81:40:31.410W 81:40:30.420W 81:40:30.827W 0:00:00.1008 Elevation -41.70m 52.60m 12.25m 7.427m UTM Easting 17 0435376.71 17 0435403.20 17 0435392.29 2.679m UTM Northing R 3405741.02 R 3405770.23 R 3405753.27 3.208m 2D Position 4.179m 3D Position 8.523m HDOP 1.0 6.4 1.60 SVs Tracking 5 8 6.86
The below plot positions were collected for 10 hours . The RTCM output of the Reference Station was at a rate of one message every 20 seconds. SAWatch calculated the 95th percentile at 8 meters. The scale of the outer ring is 15 meters.
SA Watch Statistics (editied)
First sample: 13:59:09 1.Feb.1998 - Last sample: 23:58:49
1.Feb.1998 - UTC
Elapsed time: 0:09:59:40 - Logging time: 0:09:59:40 for 17,982
records
Logging interval: 100%@2sec
Sample interval is all samples yielding 17,981 samples
Element Minimum
Maximum Mean
St Dev
Latitude 30:46:58.032N
30:46:59.706N 30:46:58.956N 0:00:00.1079
Longitude 81:40:31.404W
81:40:30.072W 81:40:30.830W 0:00:00.1025
Elevation -61.80m
59.80m 3.33m
8.158m
UTM Easting 17 0435376.77 17
0435412.49 17 0435392.20 2.722m
UTM Northing R 3405724.58 R
3405775.90 R 3405752.94 3.337m
2D Position
4.306m 0.032m
3D Position
9.225m 0.069m
HDOP
0.9
3.6
1.51
SVs Tracking 4
8
7.03
The below plot positions were collected for 12 hours 32 minutes. The RTCM output of the Reference Station was at a rate of one message every 30 seconds. SAWatch calculated the 95th percentile at 14 meters. The scale of the outer ring is 15 meters.
SA Watch Statistics (editied)
First sample: 00:01:21 2.Feb.1998 Last sample: 12:33:35
2.Feb.1998 UTC
Elapsed time: 0:12:32:14 Logging time: 0:12:32:14 for 22,569
records
Logging interval: 100%@2sec
Sample interval is all samples yielding 22,568 samples
Element Minimum
Maximum Mean
St Dev
Latitude 30:46:58.008N
30:47:00.024N 30:46:58.964N 0:00:00.1832
Longitude 81:40:31.710W
81:40:29.724W 81:40:30.828W 0:00:00.1766
Elevation -97.80m
119.50m 6.79m
14.068m
UTM Easting 17 0435368.64 17
0435421.80 17 0435392.26 4.691m
UTM Northing R 3405723.89 R
3405785.64 R 3405753.18 5.663m
2D Position
7.354m 0.049m
3D Position
15.874m 0.106m
HDOP
1.0
3.2
1.39
SVs Tracking 5
8
7.00
Garmin 45 Zero Baseline Test
The below plot positions were collected for 8 hours 24 minutes. The RTCM output of the Reference Station was at a rate of one message every 1 second. SAWatch calculated the 95th percentile at 14 meters. The scale of the outer ring is 30 meters.
SA Watch Statistics (edited)
First sample: 03:16:12 19.Jan.1998 Last sample: 11:40:50 19.Jan.1998 UTC Elapsed time: 0:08:24:38 Logging time: 0:08:24:38 for 14,591 records Logging interval: 98%@2sec 1%@5sec Sample interval is all samples yielding 14,590 samples Note: Garmin 45 Zero Baseline
Element Minimum Maximum Mean St Dev Latitude 30:46:56.400N 30:47:00.180N 30:46:58.947N 0:00:00.2093 Longitude 81:40:32.640W 81:40:29.640W 81:40:30.864W 0:00:00.2024 Elevation -46.90m 244.00m 27.35m 15.413m UTM Easting 17 0435343.62 17 0435424.06 17 0435391.29 5.377m UTM Northing R 3405674.54 R 3405790.42 R 3405752.67 6.472m 2D Position 8.415m 0.070m 3D Position 17.560m 0.145m EPE 8.3 108.8 13.27 HDOP 1.0 9.6 1.58 SVs Tracking 3 8 5.96
Garmin GPS-20 Zero Baseline Test
The below plot positions were collected for 6 hours. The RTCM output of the Reference Station was at a rate of one message every 1 second. SAWatch calculated the 95th percentile at 18 meters. The scale of the outer ring is 30 meters.
SA Watch Statistics (edited)
First sample: 17:13:45 19.Jan.1998 Last sample: 23:14:04 19.Jan.1998 UTC Elapsed time: 0:06:00:19 Logging time: 0:06:00:19 for 20,698 records Logging interval: 99%@2sec 1%@5sec Sample interval is all samples yielding 20,697 samples Note: Garmin GPS-20 Zero Baseline Element Minimum Maximum Mean St Dev Latitude 30:46:57.582N 30:47:00.174N 30:46:58.984N 0:00:00.2271 Longitude 81:40:32.004W 81:40:29.964W 81:40:30.831W 0:00:00.2170 Elevation -201.90m 105.20m 25.14m 16.362m UTM Easting 17 0435360.74 17 0435415.45 17 0435392.19 5.764m UTM Northing R 3405710.82 R 3405790.29 R 3405753.81 7.022m 2D Position 9.085m 0.063m 3D Position 18.715m 0.130m EPE 17.9 158.4 30.68 HDOP 1.1 9.7 1.85 SVs Tracking 3 6 4.73
