A Mobile Laboratory/Propagation Measurement Van (PMV) was developed to support the field experiments of the Mobile Satellite Experiment (MSAT-X) Project. This van was designed to provide flexibility, self-sufficiency and data acquisition to allow for both measurement of equipment performance and the mobile environment. The design philosophy and implementation of the PMV are described. The Pilot Field Experiments and an overall description of the three experiments in which the PMV was used are described

Berner, Jeff B.

Emerson, Richard F.

English

NASA Technical Reports Server

N88-25708
THE JPL MSAT MOBILE LABORATORY AND THE PILOT FIELD EXPERIMENTS
JEFF B. BERNER, Mobile Satellite Program, Jet Propulsion Laboratory,
California Institute of Technology, United States; RICHARD F. EMERSON,
System Subtask Manager, Mobile Satellite Program, Jet Propulsion
Laboratory, California Institute of Technology, United States.
CALIFORNIA INSTITUTE OF TECHNOLOGY
JET PROPULSION LABORATORY
4800 Oak Grove Drive 161-228
Pasadena, California 91109
United States
ABSTRACT
JPL has developed a Mobile Laboratory/Propagation
Measurement Van (PMV) to support the field experiments
of the Mobile Satellite Experiment (MSAT-X) Project.
This van was specially designed to provide flexibility,
self-sufficiency, and data acquisition to allow for
both the measurement of equipment performance and the
measurement of the mobile environment. This paper will
describe the design philosophy and implementation of
the PMV. It will then discuss the special aspects of
the PMV that are unique to Pilot Field Experiments
(PiFEx). And finally, it will provide an overall
description of the three experiments in which the PMV
has been used.
INTRODUCTION
The Mobile Laboratory/Propagation Measurement Van (PMV) was
developed to support field experiments for the Mobile Satellite
Experiment (MSAT-X) Project. Since these experiments involve both a
measurement of the environment and a measurement of the performance of
equipment specifically designed for MSAT-X, special emphasis was placed
upon flexibility, self-sufficiency and data acquisition. Following a
brief description of the PMV, these three aspects will be addressed in
more detail. In addition a brief description of the PiFEx tests that
have been conducted will be given. Finally, future plans will be
outlined.
PROPAGATION MEASUREMENT VAN
The PMV is composed of two elements-- the vehicle, itself, and the
support trailer (Figure I). These elements combine to provide the
following functions: Power; Storage; Transportation; Equipment
Mounting; Environmental Control; Support Test Equipment; Signal and
Power Distribution; and Position Location, Speed and Time.
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The vehicle portion of the PMVis a minimally modified "stretch"
1-ton Ford van with a payload capacity of 4200 pounds. The cargo
volume of 300 cubic feet is sufficient for two pairs of 4 foot
equipment racks. There is enough room between the racks for two people
to work comfortably; unfortunately there is not enough room for two
seats.
Two aspects of the van's environment are subjected to some
control: temperature and shock and vibration. Heat exchangers for the
standard truck air conditioner compressor are provided in the cab area
and in the payload area. The capacity of the compressor is
approximately 2.5 tons, which has proved sufficient even on days with
above 90° F ambient temperatures. Air circulation is provided by 48
sixty CFMfans mounted in the equipment racks and heating is supplied
by the standard truck heater. Shock and vibration are controlled to
some degree by mounting the equipment in heavy racks which are,
themselves, shock mounted to the van (Figure 2).
Laboratory instruments were included for the measurement of
frequency, time interval, power, voltage, current, spectra and
waveform. In addition, the van's position is measured by LORAN C,
speed is determined by an interface to the van's transmission, and time
is supplied by a WWI7receiver. Signal and power distribution is
through cable raceways built into the side of the van. This approach
enhances the flexibility of the van without compromising safety.
The support trailer provides storage of spares, tools, and the
equipment for the fixed station and transponder. It also provides
mounting for the motor generator which supplies the ii0 volt A/C. The
capacity of the generator is 6500 W.
Design_for Flexibility
The use of standard RETMA racks with slides allows for the
flexible placement of the equipment within the van. Eleven spare RF
cables and two spare cable raceways were included to allow a modest
amount of expansion. Nearly 100% excess A/C power capacity was
provided by the use of a 6.5 kW generator. (Future experiments are
expected to use a significant portion of this capacity.)
Desig_n for Self-Sufficiency
Spares were provided for all special equipment (MSAT-X) to the
board level and, where appropriate, to the component level. Test
equipment, tools, jigs and fixtures needed for repair and calibration
with a wide selection of test cables and adapters were included.
Emergency equipment including tire chains, trouble lamp, and battery
charger were provided.
Data Acquisition
Data acquisition was provided for in three areas: Digital, analog,
and visual.
196
Digital Data Acquisition is accomplished by an augmented
industrialized IBM PC/AT (Figure 3). Four channels of simultaneous-
sample-and-hold A to D converters were installed to collect the inphase
and quadrature outputs of the two receivers-- MSAT-Xand Reference.
Further, eight channels of multiplexed A to D converters were provided
to capture assorted slower data. Digital signals were captured with a
96 channel digital I/O card. The digital signals come from several of
the units such as the antenna controller, transceiver, speedometer and,
in the future, the terminal processor. RS-232Cand iEEE 488 interfaces
are also provided to interface with the LORANC Receiver and laboratory
instruments. The data are stored on a dual drive 20 MByte Bernoulli
box; a removable cartridge disk. Data Acquisition software provides
continuous sampling and recording of data with a modest amount of data
displayed in real time. Calibration and verification software can be
run in non-real time to validate the data acquisition process.
Analog recording was accomplished by using a 7 channel FM-FMdata
recorder capable of i0 kHz bandwidth. One of the channels is used for
calibration and compensation which improves the fidelity of the
recording.
Visual data was captured both on video tape and 35mmstill camera.
EXPERIMENTS
The PMVhas been thus far used on three major experiments: Tower-i(T-l), Satellite-la (S-la), and Tower-2 (T-2). A brief description of
each follows.
Tower-i
The Tower-I experiments were conducted in Erie CO at the NOAA Wave
Propagation Laboratory (WPL) Facility (Figure 4). This facility has a
i000 foot tower capable of supporting several hundred pounds of
equipment at any height from ground level to I000 feet. A translator
and omni antenna were mounted on the tower carriage to simulate the
spacecraft. These were illuminated from a fixed station housed in one
of the WPL shelters. The van with test equipment, units under test,
and data acquisition equipment was placed around the base of the tower
so that the tracking antenna was illuminated at various angles from 15
to 60 degrees. Antenna pattern, antenna acquisition and modem
performance tests were performed with the van stationary. In addition
to verifying the system operation (fixed site, translator and mobile
site equipments), the information gathered during these tests provides
a basis for the comparison of results during the mobile tests and data
to assist in subsystem optimization.
Antenna tracking and modem performance tests were also conducted
with the van in motion. Several tests were conducted along the north-
south road to the east of the tower. This path provided the greatest
elevation angle of all those available at the site.
197
To conduct the mobile antenna tracking tests, the signal level was
set and the antenna was acquired with the van stationary at one of the
corners. Data acquisition was started and the van accelerated to 30
MPH. The 30 MPH speed was maintained for the i mile path to the other
corner where the van was turned and driven back. A complete 2.5 minute
data block was captured in this way. (For T-l, the DAS only had the
capability to record data in 2.5 minute increments.) Tests were made
at signal levels which represent the minimum, maximum and nominal
values for the expected system.
A similar procedure was followed for the modem tests with the
parameter being the signal-to-noise ratio of the modulated signal. The
data were recorded on the analog tape recorder. The duration of the
test was determined by the recording time per tape cartridge, about 6
minutes.
Satellite-la
The S-la experiments were conducted in Santa Barbara, CA, using
the INMARSAT MARISAT satellite. This satellite provided an unmodulated
L-band carrier from a beacon transmitter which the JPL developed
mechanical antenna could track. Both the elevation angle and the
received signal strength were well below the MSAT equipment's design
values, but the experiment was still a success. Only the ability to
track a satellite was tested in this experiment; no modem test could be
done. The experiment consisted of acquiring the beacon while the PMV
was mobile and tracking the satellite while driving over roads that
provided a variety of conditions. For this experiment, the DAS was
able to take data continuously, instead of in 2.5 minute slices. Over
500 MBytes of data were collected.
Tower-2
The T-2 experiments were again conducted in Erie, CO at the WPL
Facility. This time, the main emphasis was to test the Teledyne-Ryan
Electronics phased array antenna. The same set of tests conducted at
T-I (except for the modem tests) was accomplished with the phased
array. For continuity, the mechanical antenna was also tested again at
this time.
This experiment demonstrated the flexibility of the PMV. The PMV
had to accommodate the pointing and control electronics for two
different antennas, while allowing for the ability to switch from one
antenna to the other with minimal effort and time. Also, a new
addition to the DAS allowed the operators to observe assorted pointing
information in real time. Previously, this data could only be observed
after the test.
CONCLUSIONS
The complement of equipment was found to be appropriate for the
experiments conducted during the three experiments. This will be
reviewed prior to each subsequent experiment to assure success in the
field. The data acquisition system was placed in the racks assuming
198
two people would be required to conduct the experiments. The
experience has shown that the experiments can be conducted with only
one operator. Therefore, the DASshould be moved to provide easier
access.
Approximately 750 MBytes of digital data, 280 minutes of analog
data, and several hours of video tape have been collected during the
three experiments. _=_,,_,=Ly =Liamym_m uL _,= =,t=,,= ;^_^ _^- I_; +^
improvements in the design of the mechanical antenna and the modem data
has been used in the development of the final version of the modem.
The data collected from S-la is being used by the MSAT system team to
determine fade rates and fade durations that may be encountered. Due
to the sheer mass of data that exists, complete evaluation of the data
will not be completed for some time.
FUTURE PLANS
These tests were the first of several field tests to be done with
the PMV and MSAT-X equipment. Tower-3 tests are planned for Summer of
1988 and will be used to conduct the first field end-to-end test of the
MSAT system. Real-time modem tests will be conducted and initial
verification of the Network ARQ protocol will be done.
Later this summer, the PMV will conduct the second satellite test
(S-ib). This will take place in Hawaii, again using an INMARSAT
satellite. Both of the antennae that have previously been tested and
the second phased array antenna (Ball Aerospace) will be used in the
experiment. Hawaii was selected because it will provide an elevation
angle of 50 ° to the satellite. While the configuration only supports
one way operation, this is adequate to continue performance
measurements of the antennae and to conduct realistic propagation
experiments with the L-Band satellite to mobile ground link.
ACKNOWLEDGMENTS
We appreciate the fine support that the staff at WPL provided,
particularly the help of John Gaynor, Dave Gregg and Norbert (Ski)
Szczepczynski. We also appreciate the PMV design assistance given by
Dr. W. Vogel of the University of Texas. His experience with a similar
vehicle so freely shared helped us avoid many a pitfall. Finally, a
special word of appreciation for the dedication of the JPL MSAT-X team
who accompanied us to the field: Walt Mushagian, Norman Lay, William
Rafferty, Jim Parkyn and Vahraz Jamnejad.
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I 
1 _.- 
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Figure 1: The Van and Trailer 
Figure 2: The Interior of the Van 
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Figure 3: DAS Block Diagram 
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Figure 4 :  Tower and Van in Erie 
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The JPL MSAT mobile laboratory and the pilot field experiments

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