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11941A

CLOSE-FIELD

PROBE

July

1987

Copyright

©

Hewlett-Packard

Company

1212

Valley

House

Drive

Rohnert

Park,

CA

949284999

U.S.A

CERTIFICATION

Hewlett-Packard

Company

certifies

that

this

product

met

its

published

specifications

at

the

time

of

ship¬

ment

from

the

factory.

Hewlett-Packard

further

certifies

that

its

calibration

measurements

are

traceable

to

the

United

States

National

Bureau

of

Standards,

to

the

extent

allowed

bv

the

Bureau's

calibration

facili-

n.

and

to

the

calibration

facilities

of

the

other

International

Standards

Organization

members.

WARRANTY

This

Hewlett-Packard

instrument

product

is

warranted

against

detects

in

material

and

workmanship

for

a

period

of

one

year

from

date

of

shipment.

During

the

warranty

period,

Hewlett-Packard

Company

will

at

Its

option,

either

repair

or

replace

products

which

prove

to

be

defective.

For

warranty

service

or

repair,

this

product

must

be

returned

to

a

service

facility

designated

by

HP.

Buyer

shall

prepay

shipping

charges

to

HP

and

HP

shall

pay

shipping

charges

to

returri

the

product

to

Buyer.

However,

Buyer

shall

pay

all

shipping

charges,

duties,

and

taxes

for

products

returned

to

HP

from

another

country.

HP

warrants

that

its

software

and

firmware

designated

by

HP

for

use

with

an

instrument

will

execute

its

programming

instructions

when

properly

installed

on

that

instrument.

HP

does

not

warrant

that

the

opera¬

tion

of

the

instrument,

or

software,

or

firmware

will

be

uninterrupted

or

error-free.

LIMITATION

OF

WARRANTY

The

foregoing

warranty

shall

not

apply

to

defects

resulting

from

improper

or

inadequate

maintenance

by

Buyer,

Buyer-supplied

software

or

interfacing,

unauthorized

modification

or

misuse,

operation

outside

of

the

environmental

spiecifications

for

the

product,

or

improper

site

preparation

or

maintenance.

NO

OTHER

WARRANTY

IS

EXPRESSED

OR

IMPLIED.

HP

SPECIFICALLY

DISCLAIMS

THE

IMPLIED

WARRANTIES

OF

MERCHANTABILITY

AND

FITNESS

FOR

A

PARTICULAR

PURPOSE.

EXCLUSIVE

REMEDIES

THE

REMEDIES

PROVIDED

HEREIN

ARE

BUYER’S

SOLE

AND

EXCLUSIVE

REMEDIES

HP

liable

FOR

ANY

DIRECT,

INDIRECT,

SPECIAL,

INCIDENTAL,

OR

CONSE¬

QUENTIAL

DAMAGES.

WHETHER

BASED

ON

CONTRACT,

TORT.

OR

ANY

OTHER

LEGAL

THEORY.

ASSISTANCE

Product

maintenance

agreements

and

other

customer

assistance

agreements

are

available

for

Hewlett-

Packard

products.

For

any

assistance,

contact

your

nearest

Hewlett-Packard

Sales

and

Service

Office.

Addresses

are

provid¬

ed

at

the

hack

of

this

manual.

CONTENTS

1-

1

.

General

Information

..*

^

1-2.

Description

...

^

1-4.

Accessories

Supplied.

^

1-6.

Options

..

^

1-11.

Initiallnspection.

^

2-

1

.

Specifications.

^

3-

1.

Operation

.

^

3-2.

Theory

of

Operation....

^

3-4.

Antenna

Factors.

^

3-7.

Power

Density

and

Electric

Field

Calculations..

4

3-9.

Localized

Field

Source.

^

A

3-11.

Test

Setups.

^

3-

1

6

.

Measurement

Techniques.

8

4-

1.

Operation

Verification..

4-

5.

Calibration

Cycle..

4-8.

Output

Impedance

Measurement

Test

..*.10

4-9.

Insertion

Loss

Measurement

Test

.1^

5-

1

.

Replaceable

Parts

.

1

^

5-

3.

SMA

Adapter

Replacement

Procedure.lb

5-4.

SMA

Rotary

Joint

Installation

Procedure

(Option

001)

.16

5-5.

Ordering

Information.

1

^

5-7.

Direct

Mail-Order

System.1^

6-

1

.

Factory

Returns

.

1

^

SAFETY

SYMBOLS

The

following

safety

symbols

are

used

throughout

this

manual

and

in

the

instrument.

Familiarize

yourself

with

each

of

the

symbols

and

its

meaning

before

operating

this

instrument.

A

Instrurtion

manual

symbol.

The

instrument

will

be

marked

with

this

symbol

when

it

is

necessary

for

the

user

to

refer

to

the

instruction

manual

in

order

to

protect

the

instrument

against

damage.

Location

of

pertinent

information

within

the

manual

is

indicated

by

use

of

this

symbol

in

the

table

of

contents.

Indicates

dangerous

voltages

are

present.

Be

extremely

careful.

^UTiOIM

1

CAUTION

sign

denotes

a

hazard.

It

calls

attention

to

a

procedure

which,

if

correctly

performed

or

adhered

to,

could

result

in

damage

to

or

destruction

of

the

instrument.

Do

not

proceed

beyond

a

CAUTION

sign

until

the

indicated

conditions

are

fully

understood

and

met.

rWARNING

I

WARNING

sign

denotes

a

hazard.

It

calls

attention

to

a

procedure

which,

^.

I

if

correaly

performed

or

adhered

to,

could

result

in

injury

or

loss

of

life.

Do

not

proceed

beyond

a

WARNING

sign

until

the

indicated

conditions

are

fully

understood

and

met.

HP

11941

OPERATION

NOTE

1-1.

GENERAL

INFORMATION

1-2.

Description

1-3.

The

HP

11941A

Close-Field

Probe

is

a

hand-held

electromagnetic

field

sensor

designed

to

make

repeatable,

calibrated

magnetic

field

measurements

from

9

kHz

to

30

MHz.

It

is

optimized

for

the

location

and

measurement

of

sources

of

electromagnetic

interference

(EMI)

in

electronic

equipment

The

HP

11941A

can

also

be

used

as

a

localized

magnetic

field

source

when

operated

in

conjunction

with

an

appropriate

signal

generator,

thereby

allowing

circuit-board-level

susceptibility

testing

of

instruments.

1-4.

Accessories

Supplied

1-5.

The

following

three

accessories

are

included

with

the

probe:

•

One

2m

(6.6

ft.)

double-shielded

RF

cable

with

two

SMA

(male)

end

connector,

HP

Part

Number

8120-4811

•

One

Type

N

(male)

to

SMA

(female)

adapter,

HP

Part

Number

1250-1250

•

One

BNC

(male)

to

SMA

(female)

adapter,

HP

Part

Number

1250-1700

The

double-shielded

cable

(RG-223),

reduces

measurement

errors

in

high

field

impedance

environments

by

minimizing

current

leakage

through

the

braided

coaxial

outer

conductors.

For

less

demanding

applications,

the

use

of

a

more

flexible

single-shielded

cable

type

Is

sufficient

(e.g.,

RG-58,

RG-174).

1-6.

Options

1-7.

Three

options

are

available

for

the

HP

11941

A.

1-8.

Option

001

includes

a

factory-installed

SMA

RF

Rotary

Joint

connector,

HP

Part

Number

0955-0323,

Check

Digit

5,

(See

figure

17.)

The

connector

increases

handling

flexibility

of

the

probe

by

removing

any

rotational

torque

from

the

interconnect

cable.

The

rotary

joint

is

especially

useful

when

making

measurements

using

the

double-shielded

cable.

Section

5-4

includes

instructions

on

installing

the

rotary

joint

1-9.

Option

003

consists

of

the

HP

11941A

Close-Field

Probe

without

the

double-shielded

cable

or

the

two

adapters.

1-10.

Option

910

includes

an

additional

Operation

Note.

1-11.

Initial

Inspection

1-12.

If

the

shipment

contents

are

incomplete

or

damaged,

notify

the

nearest

Hewlett-Packard

office.

If

the

shipping

container

is

damaged,

or

the

cushioning

material

shows

signs

of

stress,

notify

the

carrier

as

well

as

the

Hewlett-Packard

office.

Keep

the

shipping

materials

for

the

carrier’s

inspection.

The

HP

office

will

arrange

for

repair

or

replacement

without

waiting

for

a

claim

settlement

1-13.

See

Paragraph

4-1

for

Operation

Verification.

1

HP

11941

OPERATION

NOTE

2-1.

SPECIFICATIONS

2>2.

Specifications

for

th~e

HP

11941A

are

listed

in

table

1.

An

asterisk

(*)

placed

after

an

entry

indicates

a

supplemental

characteristic.

Supplemental

characteristics

are

not

specifications,

but

are

characteristics

included

as

additional

information

for

the

user.

2-3.

Figure

1

illustrates

the

characteristic

frequency

response

for

the

HP

11941A

Close-Field

Probe.

See

section

3-4,

Antenna

Factors,

for

additional

information.

3-1.

OPERATION

3-2.

Theory

of

Operation

3-3.

The

HP

11941A

is

a

balanced

magnetic-field

sensor

that

provides

an

output

voltage

proportional

to

the

strength

of

the

magnetic

field

at

its

tip.

Radiated

magnetic

fields

couple

directly

to

the

HP

11941A

and

produce

an

output

signal;

radiated

electric

fields

also

couple

to

the

HP

1194

lA^

but

do

not

produce

an

output

voltage

due

to

the

construction

of

the

probe.

The

HP

11941A

uses

a

dual-loop

sensor

and

a

balun

to

reject

electrically-coupled

signals.

These

loops

are

illustrated

in

figure

2,

which

shows

the

probe

with

its

non-removable

protective

tip

cover

cut

away

for

clarity.

The

probe

does

not

rectify

the

input

signal;

it

provides

both

amplitude

and

frequency

information.

It

is

ideally

suited

for

use

with

a

spectrum

analyzer.

The

HP

11941A

circuitry

is

passive

and

therefore

only

contributes

thermal

noise

to

any

measurement

system.

Inspect

the

probe

tip

for

damage

before

using,

and

do

not

use

the

probe

if

the

protective

tip

cover

is

missing

or

damaged.

3-4.

Antenna

Factors

3-5.

The

specific

antenna

factors

of

each

HP

11941A

are

measured

to

within

±2

dB

at

five

frequencies:

9

kHz,

100

kHz,

1

MHz,

10

MHz,

and

30

MHz.

This

calibration

Information

is

listed

on

the

bottom

cover

of

each

probe.

The

antenna

factors

are

given

in

the

units

of

dB(uA/m/uV).

To

calculate

the

magnetic

field

strength

in

dB(UA/m)

at

a

specific

frequency,

add

the

amplitude

of

the

measured

voltage

in

dB{uV)

(as

indicated

on

the

spectrum

analyzer)

to

the

antenna

factor

for

that

specific

frequency.

To

compensate

for

cable

losses

and

preamplifier

gains,

add

the

losses

and

subtract

the

gains

(in

dB).

Refer

to

the

following

equation:

_

H-Field

Strength

(dB

=

Vsa

+

AF

+

K

V

m

where

VsA

=

voltage

in

dBuV

measured

on

analyzer

AF

=

HP

11941A

Antenna

Factor

in

K

=

loss

or

gain

in

dB

between

HP

11941A

and

spectrum

analyzer

(Positive

value

if

loss,

negative

value

if

gain.)

2

HP

11941

OPERATION

NOTE

Table

1.

HP

11941A

Specifications

3

HP

11941

OPERATION

NOTE

3-6.

Use

the

data

included

in

figure

1

for

interpolating

antenna

factors

between

the

five

calibration

frequencies

included

in

the

probe’s

calibration

table.

3-7.

Power

Density

and

Electric

Field

Calculations

3-8.

The

HP

11941A

measures

magnetic

field

strength.

An

estimate

of

the

magnitude

of

the

associated

electric

field

can

be

made

if

a

field

impedance

is

assumed.

An

example

is

given

below

using

a

377-ohm

field

impedance.

Radiated

power

density

can

also

be

estimated,

assuming

that

the

fields

are

in

phase

and

that

the

field

impedance

is

377

ohms.

E-Field

Strength

(dB

Vsa

+

AF

+

K

+

20

log(377)

”

***

AF

+

K

+

51.5

Power

Density

7

^

Vsa

+AF

+

K

-104.3

EXAMPLE:

\

cm^

where

VsA

=

voltage

in

dBfxV

measured

on

analyzer

AF

=

HP

11941A

Antenna

Factor

in

K

*

loss

or

gain

in

dB

between

HP

11941A

and

spectrum

analyzer

(Positive

value

if

loss,

negative

value

if

gain.)

At

10

MHz,

measured

Vsa

“

65.3

dB/itV.

Let

K

*

0

and

AF

*

39

then

E

65.3

+39+

51.5=

155.8

dB^V/m

^

61.7

V/m

s(dB^)=

65.3

+

39-

104.3

=

0dB2^

=

1

^

\

cmy

cm^

cm*

3-9.

Localized

Field

Source

3-10.

The

probe

can

also

be

used

as

a

localized

magnetic

field

source

for

locating

susceptible

components

on

a

circuit

board.

It

is

a

reciprocal

device:

that

is,

a

current

fed

into

the

probe

will

generate

a

magnetic

field

at

the

dual-loop

sensor.

The

specified

antenna

factors

cannot

be

used

to

estimate

the

magnitude

of

the

output

field.

Table

2

lists

characteristic

field

strengths

developed

1

mm

(0.040

in.)

away

from

the

probe

tip,

using

an

incident

power

of

0

dBm

into

50

ohms.

CAUTION

Power

applied

to

the

probe

must

not

exceed

the

maximum

Input

power

listed

In

table

1

or

damage

to

the

probe

will

result.

4

HP

11941

OPERATION

NOTE

DUAL

LOOPS

Figure

2,

Magnetic

Field

Orientation

for

Maximum

Coupling

Table

2.

Characteristic

Magnetic

Field

Strengths

Frequency

(MHz)

Input

Power

(Into

son)

Magnetic

Field

Strength

(fi),

dB

(pA/m)

0.009

0

dBm

122

0.100

0

dBm

120

1

120

10

0

dBm

no

30

OdBm

101

3*11.

Test

Setups

3*12.

The

HP

11941A

operates

as

either

a

localized

magnetic

field

probe

or

localized

magnetic

field

source.

The

following

paragraphs

describe

different

applications

and

test

setups

for

the

probe.

Table

3

lists

the

recomrhended

test

setup

equipment

used

in

these

examples.

Any

equipment

that

satisfies

the

critical

specifications

listed

in

table

3

may

be

substituted

for

the

recommended

equipment

When

used

as

a

probe,

be

sure

to

add

the

antenna

factors

and

cable

losses

to

the

signal

levels

indicated

on

the

spectrum

analyzer.

If

a

preamplifier

is

used

to

increase

measurement

sensitivity,

subtract

its

gain

from

the

displayed

signal

level

I

WARNING

I

The

dielectric

material

on

the

tip

of

the

probe

has

a

characteristic

breakdown

voltage

of

1

kV.

To

prevent

damage

to

the

probe

and/or

personal

Injury

to

the

user,

the

probe

should

not

be

used

where

a

potential

of

over

1

kV

Is

available.

5

HP

11941

OPERATION

NOTE

3-13.

Localized

Emissions

Test

Setup:

figure

3

illustrates

a

typical

configuration

used

for

localizing

EMI

emissions.

See

section

3-16

for

proper

probe

placement

HP

8530A

SPECTRUM

ANALYZER

DEVICE

UNDER

TEST

00^0

GO

aoooD

■

■■

Qoaoa

nn

•

“

•

■■

nt-ir-inn

“

“

♦

O

B

*0

HP

11941A

AMPLIFIER

(RECOMMENDED)

OUTPUT

Figure

3.

Localized

Emissions

Test

Setup

Table

3.

Recommended

Test

Setup

Equipment

instrument

Critical

Specifications

Recommended

Model

Spectrum

Analyzer

Frequency

Range:

9

kHz-30

MHz

HP

8562A

(100

Hz-2.9

GHz)

HP

8566B

(100

Hz-300

GHz)

HP

8567A

(10

kHz-1.5

GHz)

HP

8568B

(100

Hz-1.5

GHz)

HP

8590A

(10

kHz-1.5

GHz)

Option

H51,

Close-Field

EMC

Feature

Set

HP

71

lOOA

(100

Hz-2.9

GHz)

Option

002

Tracking

Generator

'

Mt-.

Frequency

Range:

9

kHz-30

MHz

HP

8444A

(0.5-1500

MHz)

Option

059.

For

use

with

HP

8566B,

HP

8567A,

and

HP

8568B

HP

70300A

(100

Hz-2.9

GHz)

For

use

with

HP

71

lOOA

Signal

Generator

Frequency

Range:

9

kHz-30

MHz

HP

8660C

(10

kHz-2.6

GHz)

HP

8662A

(10

kHz-1280

MHz)

Preamplifier*

Frequency

Range:

9

kHz-30

MHz

RF

Gain:

>20

dB

HP

8447A

(9

kHz-50

MHz)

Option

H64

HP

8447F

(9

kHz-1.3

GHz)

Option

H64

*

An

HP

85685A

RF

Preselector

may

be

substituted

if

an

HP

8566B,

HP

8567A,

or

HP

8568B

spectrum

analyzer

is

used.

6