Measuring and Applying Antenna Patterns - Technical...

Measuring and Applying Antenna Patterns

O C E A N S E N S O R S

Tuesday, January 14, 14

Goals

• Understand why measured patterns are important

• Preparation for measuring the receive antenna pattern

• Procedures for doing walking and boat patterns


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


Why MeasureAntenna 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.


Ideal Cross Loop Pattern


Real Life Patterns


Required items for an APM

• SeaSonde transponder with charger and USB cable

• Whips

• Handheld GPS - Garmin 60 series

• Compass


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)


d > λ

Transponder Run on Land(Combined Rx,Tx Antenna)

‣ Don’t forget to walk CW & CCW

‣ Cover all bearings that Bragg echo is expected

d > λ

‣ Stay 1 λ from other objects

λ = 1 radar wavelength


d > λd > λ

RxTx

Transponder Run on Land(Separate Rx,Tx Antennas)

d > λ

‣ Don’t forget to walk CW & CCW

‣ Cover all bearings that Bragg echo is expected

‣ Stay 1 λ from other objects

λ = 1 radar wavelength


Walking Pattern(in shallow water)

Walk past sea echocutoff angles

d > 1 λ


Water

Land

Transponder Run from a Boat


Water

Land


xTest Point


Water

Land


xStart Point


Water

Land

Boat Path



Water

Land

SurfZone

Boat Path



Water

Land

SurfZone

xTransponder

on land

Boat Path



Water

Land

SurfZone

xTransponder

on land

x

Boat Path



Long Marine LabUC Santa Cruz

transponderon land

AdditionalCoverage


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!!!

What makes a Bad Pattern?


Chevron’s GenesisPlatform

• Nulls not well-defined





• Loop coupling





• Loop coupling

• Sharp spikes



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


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


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 Configurationor

__ 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:

SeaSondeModel

Bandwidth Blanking Bdlyµs

AttenuationBoat/Walking

Sweep Frequency

PulseShaping

5MHz 25kHz 60* ~4.75 15/30db** 2Hz Off12MHz 50kHz 60 ~4.75 15/30db** 4Hz Off25Mhz 150kHz 60 ~4.75 15/30db** 8Hz Off42MHz 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

! ! ! ! ! ! ! ! ! ! ! ! ** 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

FOLLOW STEPS IN THE CRIB SHEET


APM Basic Steps R7 Update 1

• Configure the receiver with SeaSondeController


SeaSondeTransponder App


Lock in Peak in SSA


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


Measuring and Applying Antenna Patterns

O C E A N S E N S O R S


Measuring and Applying Antenna Patterns - Technical...

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