AOA Benchmark

Summer 1998 saw the introduction of the next generation of AOA GPS receivers. In its ongoing role to evaluate new GPS products, UNAVCO obtained an AOA Benchmark receiver from JPL and began evaluating its performance as compared to the AOA SNR-8000 (TurboRogue).

The AOA Benchmark tracks dramatically better below 20 degrees than the TurboRogue with the current AOA chokering with standard gain antenna. We also found that the Benchmark also tracks dramatically more observations and with significantly fewer slips for low elevation satellites when using a fairly unique AOA antenna we have at UNAVCO. This high-gain antenna uses a special high gain preamplifier designed by JPL (there are only three of these antennas). The increased performance of this antenna will have to be taken into account when considering receiver options for future work.

High Rate Zero Baseline Tests

The high rate zero baseline tests were done using an AOA New Model Standard Gain Antenna (NMSG) and an AOA Antenna with JPL-Modified high gain pre-amplifiers.

Note: There are only three AOA Antenna with JPL-Modified high gain pre-amplifiers. There is one at UNAVCO (s/n 487), one at GODE (s/n 470), and one at SANT (s/n 489).

These tests consisted of two 1-hour files at the same time on two consecutive days, 1 sec sample rate, 0 elevation cut-off. Permanent Marker West (PRMW) was utilized as the antenna mount on the oof of the UNAVCO building. The bench on the roof of building Foothills Lab IV, (FL4, UCAR) was utilized as the marker for the tests run at FL4. All of the tests that were conducted with the AOA Benchmark were run in conjunction with a TurboRogue receiver.

These are files from the high rate zero baseline test at FL4.

These are the files from the high rate zero baseline test at UNAVCO

Standard Rate Zero Baseline Tests

The standard rate zero baseline tests were done using an AOA New Model Standard Gain Antenna and a High Gain Antenna. The tests consisted of two 20-hr files taken on consecutive days, 30 second sample rate, and zero elevation cut-off. These two tests were also done at the UNAVCO uilding and FL4, with the same antennas as the High rate zero baseline tests.

These are files from the standrad rate zero baseline test - FL4

These are files from the standard rate zero baseline test - UNAVCO

Comparison of the New Model Standard Gain antenna verses the High Gain antenna

Two different New Model Standard Gain Antenna’s were tested and the results were compared with the results from the JPL-Modified Antenna. The first set of data compares a TurboRogue receiver and he AOA Benchmark. This data was collected with both of the receivers being run off of a New Model Standard Gain Antenna.

In the next segment of data, you can see the difference between using a New Model Standard Gain Antenna and an JPL-Modified Antenna with the AOA Benchmark. You will see that when the benchmark is used with a New Model Standard Gain Antenna, the number of observations decrease, and the number of cycle slips increase. For example, compare bench0020.99S and bench0060.99S, and ook at the MP1: when the benchmark is used with the JPL-Modified Antenna, there are 2,585 observations in the 5-10 degree elevation range and 89 cycle slips. When the benchmark is used with the New Model Standard Gain Antenna, there are only 1,933 observations in the 5-10 degree elevation range and 494 slips.

If you compare two files for the TurboRogue; one using the New Model Standard Gain Antenna, and one using the JPL-Modified Antenna, there is no notable large difference in the number of observations or cycle slips in the 0-10 degree elevation range, in contrast to the dramatic difference that is seen when the Benchmark files are compared.

This is data for the Benchmark and a TurboRogue receiver run off of a New Model Standard Gain Antenna.

The following is the Benchmark run with a JPL-Modified Antenna, and a New Model Standard Gain Antenna. The bench0040*.* files are with the first New Model Standard Gain Antenna, the bench0060*.* files are with the second New Model Standard Gain Antenna tested, and the bench0020*.* and the bench0030*.* files are with the JPL-Modified Antenna.

The AOA Benchmark tracks dramatically better below 20 degrees than the TurboRogue with the current AOA chokering with standard gain antenna. The Benchmark tracks dramatically more observations and with significantly fewer slips for low elevation satellites when using a unique AOA antenna we have at UNAVCO. This high-gain antenna uses a special high gain preamplifier designed by JPL (there are only three of these antennas). The increased performance of this antenna will have to be taken into account when considering receiver options for future work.

Baud Rates

The Benchmark is able to download data at all of the available Baud rate settings.

Real Time Serial

The benchmark can offload data without the X-modem overhead. This was done by setting up the offload in real time serial protocol, and logging the data continously to a file. The following sample rates and baud rates were tested using the capture function in Seyon. Seyon is a complete full-featured telecommunications package for the X Window System. Seyon has many features such as: a dialing directory that supports an unlimited number of entries, a terminal emulation window that is delegated to xterm (so all the familiar xterm functions are available for use), script language to automate tedious tasks, an unlimited number of slots for external files, and support for Zmodem auto-download. These are just a few of the capabilities of Seyon. The capture function in Seyon captures data that is being sent to the screen, and saves it in a home directory. A script can also be used to capture the data, which was done for baud rate 19.2 at one second sample rate. This data is easily retrievable, and can then be translated into Rinex using teqc (for more information on teqc, go to the software section of the Developement and Testing Web Page. One must note that there will be a time delay when doing an offload in real time.

Data Found Under Testing Directory

N.M.S.G.- New Model Standard Gain Antenna
H.G. - High Gain Antenna

Send questions or comments about this page to Chuck Meertens (chuckmunavco.org) or Victoria Andreatta (victoriaunavco.org)