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UNAVCO 1996 Annual Report [Next] [Previous] [Contents]

Appendix A

UNAVCO Academic Research Infrastructure (ARI) Receiver and Antenna Test Report

C. Rocken, C. Meertens, B. Stephens, J. Braun, T. VanHove, S. Perry, O. Ruud, M. McCallum, J. Richardson

Table on Contents...

INTRODUCTION

1 Zero Baseline Tests (iv)

2 Short Baseline Tests (v)

3 QC Results (v)

4 Power tests (v)

5 Download Speed (v)

6 Real Time Kinematic Tests (vi)

7 Antenna Tests: Chamber Experiments and Mixed Baselines (vi)

1 Zero Baseline Tests (1-1)

1.1 Introduction and Experiment Description (1-1)

1.2 Pseudorange Zero Baseline Solutions (1-2)

1.3 Phase Zero Baseline Solutions (1-2)

1.4 High Rate Zerobaseline Tests (1-15)

1.5 Ambiguity Resolution Summary (1-17)

1.6 Receiver Mixing - 5 way splitter (1-22)

2 Short Baseline Tests (2-1)

2.1 Introduction and Experiment Description (2-1)

2.2 Summary of Phase and Pseudorange Solutions (2-2)

2.3 L1 Phase Solutions (2-3)

2.4 L2 Phase Solutions (2-6)

2.5 L3 Phase Solutions (2-9)

2.6 L1 Pseudorange Solutions (2-12)

2.7 L2 Pseudorange Solutions (2-15)

2.8 L3 Pseudorange Solutions (2-18)

3 QC Results (3-1)

4 Power tests (4-1)

4.1 Power Consumption (4-1)

4.2 Mid-Survey Power Failure Tests (4-2)

5 Download Speed (5-1)

5.1 Purpose (5-1)

5.2 Description (5-1)

5.3 Summary of Measurements (5-2)

5.4 Related Issues/Discussion (5-5)

5.5 Conclusions (5-7)

5.6 Receiver Options Related to Downloading (5-8)

5.7 Remote Operation Capabilities (5-10)

6 Real Time Kinematic Tests (6-1)

6.1 Purpose of Work (6-1)

6.2 Dates and Location (6-1)

6.3 Procedures (6-1)

6.4 Comments (6-3)

6.5 Comparison of Results (6-3)

6.6 Persons Contacted (6-7)

6.7 Summary of Features and specifications for Real-time Surveying Systems based on Manufacturers Brochures (6-8)

7 Antenna Tests: Chamber Experiments and Mixed Baselines (7-1)

7.1 Abstract (7-1)

7.2 Introduction (7-1)

7.3 Application of Antenna Chamber Results in GPS Software (7-2)

7.4 Horizontal Phase Centers - Rotation Tests and Antenna Chamber results (7-3)

7.5 Test of the UNAVCO/Ball Antenna Chamber Results (7-6)

7.6 Results (7-8)

7.7 Ashtech CR Antenna Dome Tests (7-9)

7.8 Results of the Dome Tests (7-10)

7.9 Conclusions and Future Work (7-11)

Appendix A

Appendix B - Summary of Observations at Table Mountain Test Site

Appendix C - Details of Download Timing Tests

Appendix D - Real-time GPS Vectors

Appendix E - Vendor Responses

INTRODUCTION

The UNAVCO GPS research community has been funded under National Science Foundations's Academic Research Infrastructure (ARI) program to purchase GPS equipment for scientific applications. There is a large variety of commercial GPS receivers available and the UNAVCO facility tested several of these instruments to aid ARI participants in selecting the appropriate receiver for their research.

The tested equipment had to satisfy several minimal requirements: (1) Full wavelength L1 and l2 carrier phase has to be tracked under A/S and non-A/S conditions, and (2) Pseudorange data are required at both GPS frequencies. The manufacturers and instruments which fulfilled the requirements and participated in these tests are given in Table 1 and include Allen Osborne Associates, Inc., Ashtech, Leica, Inc. and Trimble Navigation, Ltd. Antennas tested are given in Table 2 and Table 3 and general receiver specifications are listed in Table 4.

These tests are in many ways different from earlier tests conducted by the UNAVCO facility. The purpose of earlier tests was to find the receiver which was best suited for UNAVCO supported geodetic research. This "best" receiver was then recommended to the UNAVCO Steering Committee for purchase. The tests presented here do not intend to identify the best receiver. Different aspects may be of different importance to various investigators in the UNAVCO community. Some investigators may consider download speed or compatibility with other equipment more important than zero baseline or real time kinematic performance. Receiver costs obviously will play a major role in equipment selection.

In order to ensure optimal receiver performance using the most recent equipment and software, the vendors were invited to participate in any or all aspects of the these tests. Vendors have also reviewed drafts of this report and were invited to submit their comments, contained in Appendix E.

Tests conducted were intended to provide a wide range of information to be used by the individual investigators for selecting the appropriate receiver according to their own priorities and needs. Data for short, zero, and mixed antenna baselines were processed using the Bernese GPS software with typical processing parameters such as indicated in the ARI Vendor Ordering Agreements Exhibit A. Unless noted, the epoch interval was 30 seconds with 15 degree elevation cutoff. These tests were designed to show optimal receiver performance. Not all receiver data could, however, be processed with the same degree of automation. In particular, the AOA Turborogue and Rascal data at times required extra manual data editing and/or special tuning of default processing parameters. These problems typically, but not exclusively, occurred between 15 and 20 degrees. AOA recommends using a 20 degree cutoff when A/S is activated on the satellites. Problems encountered may differ with other processing packages.

Zero Baseline Tests

In zero baseline tests two receivers are connected to the same antenna and low-noise amplifier (LNA). These tests are conducted to examine receiver performance. All common errors due to multipath, LNA noise, propagation effects, etc. cancel in the GPS processing. Since receivers use different tracking algorithms and apply different data averaging times which can affect noise levels, some of the major differences are summarized in Table 5.

We operated all tested receivers for 5 days on zero baselines for 20 hours each day. The data were processed with the Bernese GPS software. Statistics on baseline results for L1, L2 and LC (ionosphere free combination) phase and pseudorange solutions are summarized. All receivers obtained zero baseline phase results of better than 1 mm. Pseudorange zerobaselines were better than 190 mm in all cases.

High rate (one second) epoch interval zerobaseline test results and ambiguity resolution summary are also contained in this section.

Short Baseline Tests

In short baseline tests the receivers are operated like in a typical high accuracy GPS survey application. These tests address the performance of the full system, antenna, LNAs, cables and receiver.

Each tested receiver pair was operated on several short (~5- 10 meters), known baselines. Results of the short baseline processing agreed with ground truth to 2.0 mm in the vertical and to within 1.0 mm in the horizontal for all receivers.

QC Results

Short and zero-baseline data processing were done above 15 degree elevation angles. We had operated all the receivers in the field to track to zero degree elevation angles. In this section we look at the data quality for the various receivers at very low, as well as "normal", elevation ranges. We compare the cycle slip counts, as provided by the receivers through the RINEX files. We also plot pseudorange + multipath noise and phase noise for different elevation angle ranges.

Power tests

Power consumption of the receivers is an important parameter, especially for operation at remote sites without AC power. The power needs for the tested receivers were measured and are summarized in tabular form. We also examined what happens in the case of a power failure. What happens if the power fails suddenly, what happens if it fails slowly due to draining of the battery? These are again very important considerations for remote operation of GPS sites and this section describes how the receivers respond to these conditions.

Download Speed

Exhaustive tests were run to test how fast the data from the various receivers can be downloaded for three different modes: (1) Direct connection between the receiver and computer, (2) Modem connection; (3) Radio Modem connection.

Download speed has always been an important consideration because it significantly affects field operations. With emerging permanent networks where data are downloaded from remote sites through phone lines, download speed also affects operating expenses. This section summarizes in tabular form the download performance of the tested receivers in all three modes.

Real Time Kinematic Tests

A test network had been established by UNAVCO outside Boulder, Colorado and surveyed with GPS. Three GPS manufacturers that offer real time kinematic (RTK) operation as an optional enhancement of their equipment surveyed the test network with RTK. Our report describes the demonstration and compares the RTK results with the results from our static survey. The results show that RTK accuracies are now at the cm-level, making it a very attractive technology for many scientific applications.

Antenna Tests: Chamber Experiments and Mixed Baselines

As GPS receiver performance appears to be converging, GPS antenna performance is increasingly important for the highest accuracy GPS applications. Therefore, the UNAVCO facility tested several geodetic antennas. First, we operated different antennas in the field on short baselines and compared the obtained GPS results with ground truth. Next we placed all the tested antenna types (Ashtech choke ring, AOA choke ring, Trimble SSE, Trimble SST, Leica SR399 External, AOA Rascal) in the anechoic chamber operated by BALL Aerospace, Inc. In the anechoic chamber we measured antenna phase center variations and antenna amplitude (gain) patterns as a function of direction. The resulting phase patterns from our chamber tests were applied to field data from mixed antenna (and receiver) baselines and results were compared to ground truth. We find that, using our anechoic chamber values, data from the different tested antennas can be mixed with an accuracy of about 5 mm in the vertical and 1 mm in the horizontal components when the ionospheric free linear combination LC of the GPS carriers is processed. L1 and L2 solutions are even better. If we process the same LC data but also estimate a tropospheric delay parameter every hour the vertical accuracy is still about 10 mm or better for almost all antenna pairs. The horizontal accuracy is not significantly affected by the tropospheric estimation.

GPSHIP WWW Bulletin Board

The purpose of the GPSHIP World Wide Web bulletin board and interactive email archive is to provide an information exchange forum about high-precision GPS receivers and antennas. The GPS user community and vendors are invited to submit/respond to items such as announcing new receiver firmware, new receiver hardware, antennas, data translators, bug reports, user experiences, etc. Mail messages will automatically be logged and are publicly accessible. GPSHIP is fashioned after the current UNAVCO Working Groups bulletin board. The WWW URL will be: http://unavco.org/gpship

Acknowledgments

These tests were funded by the National Science Foundation through a grant to UNAVCO. We appreciate the additional assistance by Jim Normandeau, Eric Nienhouse, Kurt Conquest, Gretchen Wallhaus, and Raphael L'Hoste-Morton. We are very grateful to all the vendors for their contributions to these tests.

Table 1: Tested Receivers

UNAVCO Name.	IGS Name	Manufacturer Model Name	P/N	Firmware
Ashtech Z-XII3	ASHTECH Z-XII3	Ashtech Z-12	700845-6 (B)	1E76
AOA Turborogue SNR-8000	ROGUE SNR-8000 (TurboRogue (field unit)	Allen Osborne Associates Turborogue SNR-8000	7490540	3.2.32.1
AOA Rascal	None Assigned yet	Allen Osborne Associates Rascal	8490330	3.0.32.0X
Trimble 4000 SSI	Trimble 4000 SSI	Trimble 4000 SSi	24840-21	7.01
Leica SR399 (see footnote)[1]	SR399E	Leica SR399E/CR344		3.4

Table 2: Tested Antennas

UNAVCO Name.	IGS Name	Manufacturer Model	Part No.	Serial #
Ashtech Chokering	DORNE MARGOLIN ASH	Ashtech Antenna L1-L2	700936(B)	11757
AOA Chokering	DORNE MARGOLIN T	Allen Osborne Associates Choke Ring	7490582-1	200
AOA Rascal	(not decided yet)	Allen Osborne Associates SR-2000	8490300	none provided by manufacturer
Trimble 4000 SST	4000ST L1/L2 GEOD (Trimble 4000ST L1/L2 GEOD used with SST and SSE receivers)	Trimble Geodetic L1/L2	14532-00	3022A00197
Trimble GEOD W/GP	TR GEOD L1/L2 GP (Trimble Geodetic L1/L2 compact with removable ground plane included used with SSE and SSi receivers)	Trimble Compact L1/L2 with removableGroundplane	23033-00	0080050642
Leica SR399 External W/GP	EXTERNAL	Leica	AT202	none provided by manufacturer

Table 3: Other Antennas used in real-time tests

UNAVCO Name.

IGS Name

Manufacturer

Model

Part No.

Ashtech Z12

GEODETIC L1/L2 L

(Ashtech patch antenna with compass, handles, built in aluminum groundplane)

Ashtech

Antenna L1-L2

700718(B)

Ashtech RTK

Ashtech

Antenna L1-L2

700700(A)

Trimble GEOD

TR GEOD L1/L2 W/O GP

(Trimble Geodetic L1/L2 compact without removable ground plane included used with SSE and SSi receivers)

Trimble

Compact L1/L2

without removableGroundplane attached

22020-00

Table 4: General Receiver Specification

	AOA Rascal	AOA Rogue SNR-8000	Trimble 4000 SSi	Ashtech Z-12	Leica SR399E
Dimensions (inches) (W x D x H)	4.1 x 8.6 x 1.9	9.5 x 12 x 2.5	9.8 x 11 x 4	8.5 x 10 x 4	9 x 9 x 4.5 (8 x 10.5 x 2.5; Controller)
Weight receiver (lbs)	2.2	9.5	6.8	8.0	4.0 (2.3; Controller)
Weight antenna (lbs)	1.5	9.5	5.8	10.0 (includes choke ring+cover)	2.1
Operating Voltage Receiver	6 VDC	9-36 VDC	10.5-35 VDC	10-32 VDC	12 VDC
Operating Voltage Antenna	5-7 VDC	12 VDC	9 VDC	12 VDC	6 VDC
Operating Temperature	-20 C to +55 C	-20 C to +55 C	-20 C to +55 C	-20 C to +55 C	-20 C to +55 C
Humidity	100%	100%	100%	100%	100%
Antenna connector (at antenna end)	N-type	N-type	N-type	N-type	TNC
Antenna connector (at receiver end)	Fisher	N-type	Lemo	N-type	TNC

Table 5: Receiver Tracking Characteristics

Receiver			phase averaging [seconds]		code averaging [seconds]
	version	mode	L1	L2	L1	L2
AOA SNR-8000	3.2	No A/S	10	10	30	30
AOA SNR-8000	3.2	A/S	10	30	30	30
AOA Rascal	3.2	No A/S	10	10	30	30
AOA Rascal	3.2	A/S	10	30	30	30
Ashtech Z-XII3	1E76-1D01	No A/S	1	1	1	1
Ashtech Z-XII3 (see footnote)[2]	1E76-1D01	A/S	1 (300)	1 (300)	1 (300)	1 (300)
Ashtech Z-12/RTZ	1J00-1D01	No A/S	1	1	1	1
Ashtech Z-12/RTZ	1J00-1D01	A/S	1 (300)	1 (300)	1 (300)	1 (300)
Leica SR399E	3.4	No A/S	1	1	300	300
Leica SR399E	3.4	A/S	1	1	300	300
Trimble 400SSi	7.04	No A/S	1	1	1	1
Trimble 400SSi	7.04	A/S	1	10	1	8

[1] The Leica datalogger unit is separate and mistakenly contained SR299E software. This resulted in less than optimal pseudorange noise values. This is discussed by Leica in Appendix E.

[2] The Ashtech Z-XII3 receiver, like the other receivers, uses the carrier phase and averaging to smooth the pseudorange observations, but with the Ashtech translator the smoothing rate can be selected at the data translation step by the user. The receiver stores the raw data with an smoothing rate of 1 second but also internally computes a smoothing correction using approximatly 300 seconds of phase observations. These corrections are stored in the raw observation file (the BEN file). The RINEX translator supplied by Ashtech, ASHTORIN, applied these corrections to the pseudorange observations when it created the RINEX file. The Bernese translator does not apply these corrections and writes the one second smoothed pseudoranges into the RINEX file.

1996 Annual Report - 25 SEP 1997

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