Slide 1

LORAN-C Band Data
Collection Efforts at
Ohio University
Presented by Curtis Cutright
to the International LORAN Association
32nd Annual Convention and
Technical Symposium
Boulder, CO
November 6, 2003


Slide 2

Outline

• Task overview
• Data collection system overview
– Airborne data collection equipment
– Lab data collection equipment
– Initial data collection results
• Task progress

Ohio University • Avionics Engineering Center


Slide 3

Task

• Field a data collection system capable of digitizing
storing atmospheric noise for subsequent analysis
• Integrate this system into an airborne flight platform

• Perform data collection under varying atmospheric
conditions

Ohio University • Avionics Engineering Center


Slide 4

Purpose

•

Develop threat models for aircraft in flight

•

Precipitation static (p-static)

•

Atmospheric noise
• Man-made noise(cross rate, CW)
• Lightning

Ohio University • Avionics Engineering Center


Slide 5

Purpose

• Identify all trade-off’s for E and H-field antennas,
SNR, phase error, saturation, bandwidth

Ohio University • Avionics Engineering Center


Slide 6

To be determined

•

Is ground-based noise the same as airborne
noise(E-field and H-field)

• Aircraft man-made noise

•

CW interference environment

•

Determine actual P-static mechanism

•

Phenomena under thunderstorms

• Antenna and pre-amp performance

Ohio University • Avionics Engineering Center


Slide 7

Data Collection

• Simultaneous ground and aircraft RF data
collection (Using DataGrabber)
• 2 channels, 16-bits samples, 400 kSamples/s

• LORAN receivers for performance assessment
• GPS WAAS for position reference

Ohio University • Avionics Engineering Center


Slide 8

Data Processing

• P-Static
• Characterize E-field and H-field antenna
performance

• Compare measured lightning noise with predicted noise
based on the national lightning detection
network(NLDN)
• Compare ground and airborne noise
• Compare airborne E-field and H-field noise
Ohio University • Avionics Engineering Center


Slide 9

Data Collection System
Overview


Slide 10

Airborne Data Collection Equipment

•

Aircraft
– King Air C-90B
– Pressurized twin turboprop
– 240 knot cruise speed

•

Equipment
– Novatel OEM4 GPS
receiver
– LORADD-DS DataGrabber
– WX-500 StormScope
– Apollo 618
– Data collection PC

Ohio University • Avionics Engineering Center


Slide 11

Whip antenna

GPS antenna

(e-field)

Apollo 618
Data Collection PC

Data
Collection
Equipment
WX-500 StormScope
Pre-amp

ADF antenna
Stormscope

(h-field)

antenna

Ohio University • Avionics Engineering Center


Slide 12

Data Collection PC
• CyberResearch dual backplane with 933MHz P-III CPU
cards
• 512MB RAM
• 160GB of hard-drive space

Ohio University • Avionics Engineering Center


Slide 13

WX-500 Stormscope
• RS-232 data output
• 200nmi range
• Heading stabilization
• Data will be used in conjunction with National Lightning
Detection Network (NLDN) data

Ohio University • Avionics Engineering Center


Slide 14

Loran-C H-Field vs. E-Field Antennas

E-Field
(Electric)
•

Large effective height

– Little voltage amplification
needed
•

High impedance (MW)

– Charge build-up (cannot be
terminated)
•

Antenna phase pattern is
omnidirectional

•

Whip or wire antenna

H-Field
(Magnetic)
• Small effective height
Large voltage
amplification needed (low
noise pre-amp)
• Low impedance (1W)
No charge build-up
(antenna is grounded)
• One loop creates 0 and 180
degrees.
• Conformal antenna

Ohio University • Avionics Engineering Center


Slide 15

Aircraft Data Collection Equipment

Ohio University • Avionics Engineering Center


Slide 16

Antennas

E-Field
II Morrow A-16

H-Field
King Radio KA42A

Ohio University • Avionics Engineering Center


Slide 17

Rackmount chassis for data collection equipment

AC in

DC Power
Supply
LORADD-DS
DataGrabber

GPS

Novatel GPS
Receiver

GPS
antenna

LAN

Antenna

Antenna

Interface

Interface

H-field

E-field

Ohio University • Avionics Engineering Center


Slide 18

LORADD-DS DataGrabber
• Sampling rate: 400kHz
• Resolution: 16 bits
• Dynamic range: 96dB
• Two input channels – sampled simultaneously
• Differential input amplifiers for the antennas
• TCP/IP data output

• Clock stability: 1ppm

Ohio University • Avionics Engineering Center


Slide 19

Antenna Interface Boxes
• Adjust received signal level
• Provide interference isolation for the antenna cable
• Impedance matching for the DataGrabber antenna
inputs

Ohio University • Avionics Engineering Center


Slide 20

Novatel GPS Receiver
• 1-20 Hz position data
• Time synchronization
• RS-232 data output (ASCII or binary)

Ohio University • Avionics Engineering Center


Slide 21

Lab Data Collection Equipment

• LORADD-DS
DataGrabber
– 400kHz sampling

– Dual channel

• Data collection PC

Ohio University • Avionics Engineering Center


Slide 22

Antennas
• E-field
– IIMorrow A-16 Whip
antenna with integral
preamplifier/impedance
transformer

– Powered by an Apollo 618
LORAN receiver

Ohio University • Avionics Engineering Center


Slide 23

Antennas
• H-field

– King KA42A ADF Loop
antenna
– Requires a separate
preamplifier/impedance
transformer tuned to the
LORAN-C band
– Powered by 5-10VDC

Ohio University • Avionics Engineering Center


Slide 24

Initial Data Collection Results

•

The next 2 slides show screen captures from the initial lab data
collection test using both antennas

•

Channel 1: h-field

•

Screen capture 1 shows the RF data from each antenna

Channel 2: e-field

– The presence of the LORAN signal can be seen in each channel
– E-field channel (bottom) has more amplification than h-field (this
does not affect the SNR)
•

Screen capture 2 shows the spectrum of the RF data

– The filter bandwidth around 100kHz is apparent
– Several CW interference sources are evident

Ohio University • Avionics Engineering Center


Slide 25

Ohio University • Avionics Engineering Center


Slide 26

Example of collected data: Time domain

Ohio University • Avionics Engineering Center


Slide 27

Ohio University • Avionics Engineering Center


Slide 28

Example of collected data: Spectrum

Ohio University • Avionics Engineering Center


Slide 29

Current Status of the Data
Collection Task


Slide 30

Airborne Collected Data

• “Clear” – 10hrs
• Overcast – 4hrs
• Close t-storm (<20nmi) – 20min
• Nearby t-storm – 2hrs
• Other – 4+hrs

Ohio University • Avionics Engineering Center


Slide 31

Data Collection Flight Tracks

Ohio University • Avionics Engineering Center


Slide 32

Thunderstorm Data Conditions

Ohio University • Avionics Engineering Center


Slide 33

Ohio University • Avionics Engineering Center


Slide 34

Ohio University • Avionics Engineering Center


Slide 35

Future Work

• Continue data collection effort
– Varying environmental conditions
– Different locations
– Correlate National Lightning Detection Network
(NLDN) data
– Mobile ground data collection equipment
• Calibrate the DataGrabber
• Aircraft noise analysis
Ohio University • Avionics Engineering Center


Slide 36

Acknowledgements

• Mitch Narins (FAA)
• Wouter Pelgrum (Reelektronika)
• Bryan Branham (Ohio University)
• Jay Clark (Ohio University)

Ohio University • Avionics Engineering Center


Slide 37

Questions?