Initial RF Ingress Measurements for Coaxial and UTP Cables from

Automotive BCI Test

Larry Cohen

Ramin Shirani

1

Outline

• Overview

• BCI Test Procedure (to 400 MHz)

• BCI Setup

• BCI test results (MDI voltage)

• Observations

• Setup for > 400 MHz

• Next Steps

2

Overview

• Main Purpose: Initial measurement of the induced MDI port voltage from a standard automotive radiated immunity bulk current injection (BCI) test with different automotive harness cable types

–BCI test method is defined in ISO 11452-4; this procedure is generally used only up to 400 MHz for testing RF immunity of cable harnesses

–Test three different cable media:

• Single-shield RG174 (1.9 meter sample)

• PE-C100 (double-shielded RG174, 1.9 meter sample)

• UTP (single pair in jacket, 5 meter sample)

–All coaxial cable samples used FAKRA connectors

3

Procedure for Measurement of MDI Port Voltage from a BCI Test• Perform the calibration procedure in Annex A of ISO 11452-4 to determine the required BCI probe input power to inject 50 mA of

common-mode current at each frequency point (substitution method)

• Build the BCI test setup (page 4) with the automotive cable harness and connected to the far-end termination block; set the location of the BCI probe 45 cm from the MDI port

• Use the control PC to disable the evaluation platform PHY transmitter and echo canceller, set the PHY receiver gain blocks to known states, initiate continuous ADC buffer capture, and send the ADC buffer contents to the control PC over the USB

• Turn on the BCI drive amplifier and initiate the BCI frequency sweep; the sweep is from 33 MHz to 399 MHz at 2 MHz steps, dwell time of 2 seconds at each frequency point (after proper power leveling), test signal is an unmodulated CW signal

• When the BCI sweep is complete, apply post processing to the captured buffer data to determine the ADC capture level at each frequency point

• Connect an RF signal generator set at a known reference level (-20 dBm) to the MDI port and perform the same above sweep, buffer capture, and post processing to determine ADC capture level at each frequency point; this is the MDI port reference level sweep

• Determine the MDI port voltage from the BCI test by comparing and scaling the ADC capture levels from the BCI test to the corresponding data from the MDI port reference level sweep

• Scale the measured RF ingress voltage data to match a selected BCI test current condition template (e.g. GMW3097) with the difference between the test current level and test condition template and add any modulation level offset; plot the final result

• Note: The continuous ADC sample buffer procedure defined above does not require any synchronization connection with the EMC lab test equipment

4

Test Setup for BCI RF Ingress Measurement on Automotive Cable

5

Aquantia

PHY

Ev aluation

Board

Ground plane

table (90 cm

above floor)

GP

IB

RF Power Amplifier

(AR 50W-1000A)

Shielded chamber

Signal

Generator50

50

GPIB GPIB

50

Insulating cable

support

(~5 cm thick)

Bulk current injection

(BCI) probe

(FCC F-130-1)

Ferrite

clamp

INOUT

50

Directional

Coupler (40 dB)

FWD

CPL

Spectrum

Analyzer / RF

Power Meter

50

GPIB Control

Host PCGP

IB

Evaluation

Board Control

PC

US

B

Automotive cable channel

(UTP or coax)

The spectrum analyzer is used to monitor the

signal power to the BCI probe. At each frequency,

the signal generator output is adjusted to match

the calibration level at that frequency.

Unmodulated

CW signal

USB

Cable

Adapter

d

Shielded enclosure(Sits on 2 cm of

insulating material)

BCI probe calibrated as per Annex

A of ISO 11452-4 to 50 mA

(substitution method)

Sweep with BCI probe 45 cm from

the PHY platform (d = 45 cm), 30

MHz to 400 MHz

The DUT PHY transmitter and

echo canceller are disabled

(quiet) while the receiver is set

for continuous ADC buffer

capture. The contents of each

buffer capture is sent to the

control PC during the BCI

sweep.

The ingress levels at each

frequency are obtained from

post-processing of the

captured ADC buffer data.

Termination Block(Common ground

connected to ground

plane table)

120 VAC to +12 VDC

power supply inside

shielded enclosure

(+12 VDC is f loating)

+12

VDC

Power

Line Filter

Isolation

Transformer

120

VAC

Power

Converter

Filtered

Power

Mains

120

VAC

Earth ground

disconnected

To determine the actual MDI

port voltage, we perform a

reference capture sweep by

connecting a signal generator

with a known signal level (-20

dBm) directly into the MDI port

of the Evaluation Board.

Test Setup for BCI RF Ingress Measurement on Automotive Cable

6

7

Observations

• The observed RF ingress coupling from single-shielded coaxial cable (RG174) is considerably worse than double-shielded coaxial cable (PE-C100) and actually on par with UTP cable

• The induced MDI port voltage with (double-shielded) coaxial cable is at least 20 dB less than the corresponding MDI port voltage with UTP cabling at most frequency points

–Shield construction and termination matters !!

• The BCI test current was set at 50 mA to due to test equipment limitations

–Use of reduced test currents simplifies test setup by allowing simple copper cable interconnects instead of fiber optics

–This is permissible since we can simply scale the final measured results for a desired test template condition

• The different peak/null pattern in the UTP measurement is due to the longer cable sample that was tested (5m for UTP vs. 1.9m for coaxial cable samples)

8

Tests > 400 MHz

• Need to define a standard methodology to measure the RF ingress from different cable samples from 1 MHz to at least 3 GHz;

–BCI test methods to 400 MHz as shown here

• Need radiative immunity test for higher frequencies

• Existing standard ALSE (ISO 11452-2) test methods are recommended

9

ALSE Test Setup to Measure RF Ingress from 400 MHz to 3 GHz

10

Ground plane

table (90 cm

above floor)

1 meter

1.5 meters

DUT cable harness total

length < 2 meters

GPIB Control

Host PC GP

IB

Balun

RF Power

Amplifier

Antenna

(1 meter height)

Absorber-lined

shielded chamber

(ALSE)

Signal

Generator50

50

GPIB GPIB

50

Insulating cable

support

(5 cm thick)

DUT cable harness

must be 10 cm from the

edge of the table

Signal generator calibrated to

generate a known E-field level. This

eliminates the need for the E-field

sensor and field strength meter.

Control PC

GP

IB

Shielded

coaxial cable

Test field strength:

10 V/m to 30 V/m from 400 MHz to 2000 MHz (CW)

Use of test field strengths lower than that specified on

actual test (e.g 10 V/m) allows use of simple copper cable

interconnects in the scope capture interface (eliminates

need to use fiber optics). Measured result can be scaled

as necessary for higher field strengths.

Termination Block(Common ground

connected to ground

plane table)

0.1

meter

Shielded

enclosure

Shielded enclosure(Sits on 2 cm of

insulating material)

Cable

Adapter

Board

Digital Storage

Oscilloscope

(> 5GHz BW) GP

IB

The DSO is set to continuously

capture digitized input waveform

records and send them to the

control PC throught the GPIB

during the frequency sweep.

The ingress levels at each

frequency are obtained from

post-processing of the captured

data.

Use of DSO eliminates

bandwidth limitations of

PHY receiver

>1.5 meters

To determine loss or scaling

effects from cable adapter

board, we perform a reference

capture sweep by connecting

a signal generator with a

known signal level (-20 dBm)

directly at the Cable Adapter

Board MDI port

Next Steps

• Identify cable samples for future testing:

–STP cable, UTP cable in bundles

–Automotive cable setup input appreciated from OEMs

• Perform RF ingress measurement on cable samples up to 3 GHz using the BCI tests as here + absorber-lined shielded enclosure (ALSE) methodology defined in ISO 11452-2

11

Thank you.