Measuring and Applying Antenna Patterns

Measuring and Applying
Antenna Patterns
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Tuesday, January 14, 14
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Goals
• Understand why measured patterns are
important
• Preparation for measuring the receive
antenna pattern
• Procedures for doing walking and boat
patterns
Tuesday, January 14, 14
Antenna Pattern
Measurement
• The measurement of the phase and
amplitudes of loop 1 and loop 2 in relation
to the monopole/dipole
• Important for making velocity measurements
at correct bearings
• Reveals distortions in a pattern that could
lead to suspect data
Tuesday, January 14, 14
Why Measure
Antenna Patterns?
•
Antennas interact or “couple” with other conductive or
ferromagnetic material.
•
It is difficult to isolate HF antennas from objects with
potential to interact - rule of thumb is > 1 λ separation.
•
Distorted antenna patterns cause bearing errors which, in
turn, cause current velocity errors.
•
Radials derived from measured patterns are always more
accurate than those derived from ideal - gaps or no.
•
Sometimes the pattern is too distorted to DF for currents
and the antenna must be moved - this may not be evident
from radial coverage alone.
Tuesday, January 14, 14
Ideal Cross Loop Pattern
Tuesday, January 14, 14
Real Life Patterns
Tuesday, January 14, 14
Required items for an APM
•
SeaSonde
transponder with
charger and USB
cable
•
•
Whips
•
Compass
Handheld GPS Garmin 60 series
Tuesday, January 14, 14
Other Required Items
• Three 8 foot (2.438 meter) whip antennas
for a walking pattern
• 4 piece green whip antenna with specialized
transmit cable for boat antenna pattern
measurements
• Walkie talkie radios
• CODAR APM crib sheet (found in users
manual)
Tuesday, January 14, 14
Transponder Run on Land
(Combined Rx,Tx Antenna)
d>λ
d>λ
λ = 1 radar wavelength
‣ Cover all bearings
that Bragg echo is
expected
Tuesday, January 14, 14
‣ Don’t forget to walk ‣ Stay 1 λ from other
CW & CCW
objects
Transponder Run on Land
(Separate Rx,Tx Antennas)
d>λ
d>λ
Tx
d>λ
Rx
λ = 1 radar wavelength
‣ Cover all bearings
that Bragg echo is
expected
Tuesday, January 14, 14
‣ Don’t forget to walk ‣ Stay 1 λ from other
CW & CCW
objects
Walking Pattern
(in shallow water)
Walk past sea echo
cutoff angles
d>1λ
Tuesday, January 14, 14
Transponder Run from a Boat
Water
Land
Tuesday, January 14, 14
Transponder Run from a Boat
Test Point
x
Water
Land
Tuesday, January 14, 14
Transponder Run from a Boat
x
Water
Start Point
Land
Tuesday, January 14, 14
Transponder Run from a Boat
Boat Path
Water
Land
Tuesday, January 14, 14
Transponder Run from a Boat
Boat Path
Water
Land
Tuesday, January 14, 14
Transponder Run from a Boat
Boat Path
Water
Land
Tuesday, January 14, 14
Surf
Zone
Transponder Run from a Boat
Boat Path
Water
Land
Tuesday, January 14, 14
Surf
Zone
Transponder Run from a Boat
Boat Path
Water
Land
Tuesday, January 14, 14
Surf
Zone
Transponder Run from a Boat
Boat Path
Surf
Zone
Water
Land
x
Transponder
on land
Tuesday, January 14, 14
Transponder Run from a Boat
Boat Path
Surf
Zone
Water
Land
x
Transponder
on land
Tuesday, January 14, 14
Transponder Run from a Boat
Boat Path
Surf
Zone
Water
Land
Tuesday, January 14, 14
x
x
Transponder
on land
Long Marine Lab
UC Santa Cruz
Additional
Coverage
Tuesday, January 14, 14
transponder
on land
What makes a Bad Pattern?
The Carpinteria Pier
•
Lots of vertical metal
near antenna
•
The pier itself may have
significant amounts of
iron
•
The metal in the cranes
move so the antenna
pattern is not static!!!
Tuesday, January 14, 14
What makes a Bad Pattern?
Chevron’s Genesis
Platform
•
Nulls not well-defined
Tuesday, January 14, 14
What makes a Bad Pattern?
Chevron’s Genesis
Platform
•
Nulls not well-defined
•
Loop coupling
Tuesday, January 14, 14
What makes a Bad Pattern?
Chevron’s Genesis
Platform
•
Nulls not well-defined
•
Loop coupling
•
Sharp spikes
Tuesday, January 14, 14
What makes a Bad Pattern?
Chevron’s Genesis
Platform
•
Nulls not well-defined
•
Loop coupling
•
Sharp spikes
Tuesday, January 14, 14
What makes a bad pattern?
Summary
•
•
•
•
•
Loop pattern is missing nulls
Loop amplitudes are out of balance
Loop amplitudes (or phases) couple over angular sector
Lots of spikes or nulls - multiple valued
Monopole has sharp spikes or nulls
Tuesday, January 14, 14
APM Basic Steps
• DO A TEST RUN BEFORE YOU HIRE A
BOAT
• Configure the receiver with SeaSondeController
and the transponder with the Transponderapp
• Enable loop diagnostics in SeaSondeAqcuisition
• Test the transponder on land for signal peak and
lock in the peak
• Log TimeSeries at the radar site, log GPS track on
the boat or while walking
• Watch the peak in SeaSondeAqcuisition during
the APM, if it disappears, troubleshoot
Tuesday, January 14, 14
FOLLOW STEPS IN THE CRIB SHEET
APM Crib Sheet For SeaSonde Transponder Application
April 15, 2013 (rev 11)
One to Two Weeks in Advance
__Check transponder battery & charge > 12 volts (a new battery will be > 13 volts when fully charged)
Day of APM
__Synchronize the computer to GPS clock and confirm site and antenna are functioning properly
__Quit all applications except SeaSondeController and SeaSondeAcquisition
__Stop logging cross spectra, checkmark “Enable Loop Diagnostics” (formerly “Diagnostic Processing”
CONFIGURE RECEIVER with R7 using SeaSondeController->Receiver Controller->Receiver APM Configuration
or
__ STORE receiver’s normal operating settings in AWG register 3 (in SEND box: type save 3, press enter key)
__ CONFIGURE RECEIVER with APM Settings as follows and then store the settings in AWG register 2:
SeaSonde
Model
Bandwidth
Blanking
Bdly
µs
Attenuation
Boat/Walking
Sweep
Frequency
Pulse
Shaping
5MHz
25kHz
60*
~4.75
15/30db**
2Hz
Off
12MHz
50kHz
60
~4.75
15/30db**
4Hz
Off
25Mhz
150kHz
60
~4.75
15/30db**
8Hz
Off
42MHz
150kHz
60
~4.75
15/30db**
8Hz
Off
* Note: Older model 5MHz systems will not accept 60us, use 120us in this case
** Reduce Attenuation if Transponder doesn’t respond.
Configure Transponder
__Connect USB cable between XPNDR and Mac laptop and launch SeaSonde Transponder Application
__CONFIGURE TRANSPONDER by clicking “INITIALIZE” button in SeaSonde Transponder application
THE AUTOMATIC SETTINGS IN THE TRANSPONDER APPLICATION WILL PLACE THE TRANSPONDER PEAK IN RANGE
CELL 10 (+/- 2 RC’S) APPROXIMATELY 75% TO THE RIGHT OF CENTER OF THE SEASONDE ACQUISITION SPECTRAL
PLOT WINDOW FOR ALL SYSTEMS
__Save settings to the transponder (press STORE button) and verify that they remain after cycling power
CONFIGURE TRANSPONDER ANTENNA as indicated below:
SeaSonde Model
!
!
!
Antenna Configuration
(Boat Run-APM)
**Antenna Configuration
(Walking-WAPM)
5MHz
12MHz head w/green antenna + OCEAN GND three 8’ white whips on sides and top
12MHz
12MHz head w/green antenna + OCEAN GND three 8’ white whips on sides and top
25Mhz
White whips (2 - 4’ whips on sides + 8’ on top)
two 4’ white whips on sides and 8’ top
42MHz
White whips (2 - 4’ whips on sides + 4’ on top)
three 4’ White whips on sides and top
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** A single vertical whip may be adequate for WAPM
__Turn off all SeaSondes operating at the same frequency that are within range
__Place transponder > 1 wavelength from receive antenna and test
__Identify the peak in the Doppler spectra plot and check for Time Series (Lvl) file creation. Save screenshot.
__Note range cell number, signal strength (dBm) and Doppler bin number of transponder peak
__Collect two shore-based data points (ends of the arc) with the transponder and handheld GPS
!
At the boat:
__Check boat & assemble transponder antenna
__Install antenna so it is not blocked to either side & configure antenna sea water ground if using green whip
__Configure (or confirm) Transponder Settings
__Clear GPS memory then configure the GPS for logging every 1-5 seconds and also to “stop when full”
__Turn off GPS and proceed to position where antennas are visible from boat
__Turn handheld GPS receiver on and confirm it is logging data. Place it in safe location with 5+ satellites visible
!
At the receiver:
__Boat proceeds to center of arc a few ~ 100-300m offshore to provide good signal for testing
__Identify the peak in the Diagnostics window, start logging Time Series and check for Lvl file creation
__Boat proceeds to starting point of 1st arc to begin the pattern
__Confirm peaks in channels 1, 2 and 3 as transponder travels through its arcs- ideal peak strength -90 to -120dB
__After completing second arc, turn off handheld GPS
__Restore operating settings (in SEND box enter: load 3 to recover settings) and then STORE. Restart the computer
__Verify SeaSonde settings have returned to normal operational values and that they have been stored
Tuesday, January 14, 14
APM Basic Steps
R7 Update 1
• Configure the
receiver with
SeaSondeController
Tuesday, January 14, 14
SeaSondeTransponder App
Tuesday, January 14, 14
Lock in Peak in SSA
Tuesday, January 14, 14
Lock in Peak in SSA
Tuesday, January 14, 14
Ready to do APM
• Test the transponder on land for signal
peak and lock in the peak
• Log TimeSeries at the radar site, log
GPS track on the boat or while walking
• Watch the peak in SeaSondeAqcuisition
during the APM, if it disappears,
troubleshoot
Tuesday, January 14, 14
Measuring and Applying
Antenna Patterns
O
Tuesday, January 14, 14
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