Keysight 8478B Operating And Service Manual

Keysight 8478B
Thermistor Mount

Operating and Service Manual

Notices

© Keysight Technologies

1981-2018

No part of this manual may be
reproduced in any form or by any
means (including electronic storage
and retrieval or translation into a
foreign language) without prior
agreement and written consent from
Keysight Technologies, Inc. as
governed by United States and
international copyright laws.

Manual Part Number

08478-90015

Edition

Edition 3, March 2018

Printed in:

Printed in Malaysia

Published by:

Keysight Technologies
Baya n Lepas Free Industrial Zone,
11900 Penang, Malaysia.

Technology Licenses

The hardware and/or software
described in this document are
furnished under a license and may be
used or copied only in accordance
with the terms of such license.

Declaration of Conformity

Declarations of Conformity for this
product and for other Keysight
products may be downloaded from
the Web. Go to

http://www.keysight.com/go/confor
mity. You can then search by product

number to find the latest Declaration
of Conformity.

U.S. Government Rights

The Software is “commercial
computer software,” as defined by
Federal Acquisition Regulation
(“FAR”) 2.101. Pursuant to FAR

12.212 and 27.405-3 and
Department of Defense FAR
Supplement (“DFARS”) 227.7202, the
U.S. government acquires
commercial computer software
under the same terms by which the
software is customarily provided to

the public. Accordingly, Keysight
provides the Software to U.S.
government customers under its
standard commercial license, which
is embodied in its End User License
Agreement (EULA), a copy of which
can be found at

http://www.keysight.com/find/sweul
a The license set forth in the EULA

represents the exclusive authority by
which the U.S. government may use,
modify, distribute, or disclose the
Software. The EULA and the license
set forth therein, does not require or
permit, among other things, that
Keysight: (1) Furnish technical
information related to commercial
computer software or commercial
computer software documentation
that is not customarily provided to
the public; or (2) Relinquish to, or
otherwise provide, the government
rights in excess of these rights
customarily provided to the public to
use, modify, reproduce, release,
perform, display, or disclose
commercial computer software or
commercial computer software
documentation. No additional
government requirements beyond
those set forth in the EULA shall
apply, except to the extent that those
terms, rights, or licenses are
explicitly required from all providers
of commercial computer software
pursuant to the FAR and the DFARS
and are set forth specifically in
writing elsewhere in the EULA.
Keysight shall be under no obligation
to update, revise or otherwise modify
the Software. With respect to any
technical data as defined by FAR

2.101, pursuant to FAR 12.211 and

27.404.2 and DFARS 227.7102, the
U.S. government acquires no greater
than Limited Rights as defined in FAR

27.401 or DFAR 227.7103-5 (c), as
applicable in any technical data.

Warranty

THE MATERIAL CONTAINED IN THIS
DOCUMENT IS PROVIDED “AS IS,”
AND IS SUBJECT TO BEING
CHANGED, WITHOUT NOTICE, IN
FUTURE EDITIONS. FURTHER, TO
THE MAXIMUM EXTENT PERMITTED
BY APPLICABLE LAW, KEYSIGHT
DISCLAIMS ALL WARRANTIES,
EITHER EXPRESS OR IMPLIED WITH
REGARD TO THIS MANUAL AND
ANY INFORMATION CONTAINED

HEREIN, INCLUDING BUT NOT
LIMITED TO THE IMPLIED
WARRANTIES OF
MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE.
KEYSIGHT SHALL NOT BE LIABLE
FOR ERRORS OR FOR INCIDENTAL
OR CONSEQUENTIAL DAMAGES IN
CONNECTION WITH THE
FURNISHING, USE, OR
PERFORMANCE OF THIS
DOCUMENT OR ANY INFORMATION
CONTAINED HEREIN. SHOULD
KEYSIGHT AND THE USER HAVE A
SEPARATE WRITTEN AGREEMENT
WITH WARRANTY TERMS
COVERING THE MATERIAL IN THIS
DOCUMENT THAT CONFLICT WITH
THESE TERMS, THE WARRANTY
TERMS IN THE SEPARATE
AGREEMENT WILL CONTROL.

Safety Notices

A CAUTION notice denotes a hazard. It
calls attention to an operating
procedure, practice, or the like that,
if not correctly performed or adhered
to, could result in damage to the
product or loss of important data. Do
not proceed beyond a CAUTION
notice until the indicated conditions
are fully understood and met.

A WARNING notice denotes a hazard.
It calls attention to an operating
procedure, practice, or the like that,
if not correctly performed or adhered
to, could result in personal injury or
death. Do not proceed beyond a
WARNING notice until the indicated
conditions are fully understood and
met.

Keysight 8478B Thermistor Mount

Operating and Service Manual

Certification

Keysight Technologies certifies that this product met its published
specifications at the time of shipment. Keysight further certifies that its
calibration measurements are traceable to the United States National Institute
of Standard and Technology (formerly National Bureau of Standards), to the
extent allowed by that organization’s calibration facility, and to the calibration
facilities of other International Standards Organization members.

General Warranty

The material contained in this document is provided “as is,” and is subject to
being changed, without notice, in future editions. Further, to the maximum
extent permitted by applicable law, Keysight disclaims all warranties, either
express or implied with regard to this manual and any information contained
herein, including but not limited to the implied warranties of merchantability
and fitness for a particular purpose. Keysight shall not be liable for errors or for
incidental or consequential damages in connection with the furnishing, use, or
performance of this document or any information contained herein. Should
Keysight and the user have a separate written agreement with warranty terms
covering the material in this document that conflict with these terms, the
warranty terms in the separate agreement shall control. Duration and
conditions of warranty for this product may be superseded when the product is
integrated into (becomes a part of) other Keysight products. During the
warranty period, Keysight will, at its option, either repair or replace products
which prove to be defective. The warranty period begins on the date of delivery
or on the date of installation if installed by Keysight.

Warranty Service

For warranty service or repair, this product must be returned to a service facility

designated by Keysight. For products returned to Keysight for warranty service,
the Buyer shall prepay shipping charges to Keysight and Keysight shall pay
shipping charges to return the product to the Buyer. However, the Buyer shall
pay all shipping charges, duties, and taxes for products returned to Keysight
from

another country.

3

-

Certification
Limitation of Warranty

Limitation of Warranty

The foregoing warranty shall not apply to defects resulting from improper or
inadequate maintenance by the Buyer, Buyer-supplied products or interfacing,
unauthorized modification or misuse, operation outside of the environmental
specifications for the product, or improper site preparation or maintenance.

The design and implementation of any circuit on this product is the sole
responsibility of the Buyer. Keysight does not warrant the Buyer’s circuitry or
malfunctions of Keysight products that result from the Buyer’s circuitry. In
addition, Keysight does not warrant any damage that occurs as a result of the
Buyer’s circuit or any defects that result from Buyer-supplied products.

To the extent allowed by local law, Keysight makes no other warranty,
expressed or implied, whether written or oral with respect to this product and
specifically disclaims any implied warranty or condition of merchantability,
fitness for a particular purpose, or satisfactory quality.

Exclusive Remedies

To the extent allowed by local law, the remedies provided herein are the
Buyer’s sole and exclusive remedies. Keysight shall not be liable for any direct,
indirect, special, incidental, or consequential damages (including lost profit or
data), whether based on warranty, contract, tort, or any other legal theory.

4 Keysight 8478B Thermistor Mount

Certification
Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC

Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC

This instrument complies with the WEEE Directive (2002/96/EC) marking
requirement. This affixed product label indicates that you must not discard this
electrical or electronic product in domestic household waste.

Product category

With reference to the equipment types in the WEEE directive Annex 1, this
instrument is classified as a “Monitoring and Control Instrument” product.

The affixed product label is as shown below.

Do not dispose in domestic household waste.

Sales and Technical Support

To contact Keysight for sales and technical support, refer to the support links
on the following Keysight websites:

• www.keysight.com/find/powersensors
(product-specific information and support, software and documentation
updates)

• www.keysight.com/find/assist
(worldwide contact information for repair and service)

Keysight 8478B Thermistor Mount 5

-

Certification
Sales and Technical Support

6 Keysight 8478B Thermistor Mount

Table of Contents

Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

General Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Warranty Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Limitation of Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Exclusive Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC . . . . . . . . . . . . . . . 5

Product category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Sales and Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1. General Information

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Instruments Covered By Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Incoming Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Contents

2. Operation

Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Mechanical Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Biasing Thermistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Maximum Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Average Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Pulse Energy and Peak Power for 8478B/432 Combination. . . . . . . . . . . . . . . . . . . . . . . 17

Pulse Energy and Peak Power for 8478B/431 Combination. . . . . . . . . . . . . . . . . . . . . . . 17

Drift Precaution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Operation with 431A/B/C or 430 Power Meters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Zero Set. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

RF Power Turned Off for Zero-Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Unbalanced Operation with Model 431A/B/C and 430 Power Meters. . . . . . . . . . . . . . . 20

Balanced Operation with Model 431C Power Meter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8478B/432 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Mount Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Calibration Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Effective Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Calibration Data Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Thermoelectric Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Thermoelectric Effect Error Correction for 8478B/431 Combination . . . . . . . . . . . . . . . . 23

Thermoelectric Error for 8478B/432 Combination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Keysight 8478B Operating and Service Manual 7

Contents

3. Operating Principles

General Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Operation with 432 Power Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Operation with 431 Power Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

432 Power Detection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

431 Power Meter Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

4. Maintenance

Mechanical Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Performance Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

SWR Measurement, 8GHz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

SWR Measurement, 15 and 18GHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Thermistor Resistive Match Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Thermistor Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Repair and Recalibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

A.Manual Changes

CHANGE A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

CHANGE B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

CHANGE C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

8 Keysight 8478B Operating and Service Manual

Keysight 8478B Thermistor Mount

Operating and Service Manual

1 General Information

Introduction 10
Specifications
Instruments Covered By Manual
Incoming Inspection

10

10

11

This chapter contains information about initial inspection and overview of the
Keysight 8478B Thermistor Mount.

9

1-

General Information
Introduction

Introduction

The Keysight Model 8478B Coaxial Thermistor Mount is designed for use with
Keysight Model 431 and 432 Power Meters to measure microwave power from
1μW to 10mW. Design of the mount minimizes adverse effects from
environmental temperature changes during measurement. For increased
measurement accuracy, Effective Efficiency and Calibration Factor are
measured for each mount at selected frequencies across the operating range;
the results are marked on the label of the instrument (see “Mount Calibration”

on page 21). The Model 8478B can be used over the 10MHz to 18GHz

frequency range. Throughout the range, the mount terminates the coaxial
input in a 50-ohm impedance, and has a SWR of not more than 1.75 without
external tuning.

Each mount contains two series pairs of thermistors, which are matched to
cancel the effects of drift with ambient temperature change. Thermal stability
is accomplished by mounting the leads of all four thermistors on a common
thermal conductor to ensure a common thermal environment. This conductor
is thermally insulated from the main body of the mount so the thermal noise or
shocks applied externally to the mount, such as those from handling the mount
manually, cannot significantly penetrate to disturb the thermistor. This thermal
immunity enables the thermistors to be used in the measurement of microwave
power down to the microwatt region.

The 8478B operates directly with 431C and 432 Power Meters. Model 11527A
adapter is used for operation with 431A/B Power Meters. Model 11528A is
used for operation with 430 Power Meters.

Specifications

The specifications are listed in “Specifications” on page 15. These
specifications are the performance standards against which the Thermistor
Mount/Power Meter operation is compared.

For operation with the 431 Power Meter, add the following uncertainties to
those indicated in Table 2-1: for 0.3mW range, ±0.3%; for 0.1mW range,
±0.7%; for 0.03mW range, ±1.5%; for 0.01mW range, ±2.8%. The power range
in which the 431/8478B operates is 1μ

Instruments Covered By Manual

This manual applies directly to instruments with serial numbers prefixed
2106A. With the backdating found in Appendix A, the manual also applies to
instruments with serial number prefixed 2030A and below.

W to 10mW.

10 Keysight 8478B Thermistor Mount

General Information
Incoming Inspection

Incoming Inspection

Inspect the Model 8478B upon receipt for mechanical damage. Also check it
electrically; if the mount was subjected to severe mechanical shock during
shipment, the match between the thermistors may be affected. To check
thermistor match, proceed as described in “Performance Tests” on page 32.

If any damage is found, inform the carrier and your nearest Keysight sales and
Service office immediately.

Keysight 8478B Thermistor Mount 11

1-

General Information
Incoming Inspection

12 Keysight 8478B Thermistor Mount

Keysight 8478B Thermistor Mount

Operating and Service Manual

2 Operation

Precautions 14
Specifications
Drift Precaution
Zero Set
Mount Calibration
Calibration Data Application
Thermoelectric Effect

15

20

19

21

22

23

This chapter contains information about specifications and operation of the
Keysight 8478B Thermistor Mount.

13

2-

Operation
Precautions

Precautions

Mechanical Shock

DO NOT SUBJECT THE MOUNT TO MECHANICAL SHOCK. Shock may
destroy the match between thermistors and increase susceptibility to drift.

Biasing Thermistors

Before connecting the 8478B to a 431C or 432-series Power Meter, set the
MOUNT RES switch to the 200Ω
prefixed below 1833A, set the MOUNT RES switch to 200Ω BAL (431) or
200Ω (432).

When using the 8478B with 431A/B or 430 Power Meter, use Model
11527A or 11528A Adapter respectively and set MOUNT RES switch to
200Ω position. Connecting a 200-ohm mount to a power meter set for a
100-ohm mount can result in thermistor damage.

position. For Mounts with serial numbers

14 Keysight 8478B Thermistor Mount

Operation
Specifications

Specifications

Frequency Range: 10MHz to 18GHz

Table 2-1 Uncertainty of Calibration Factor Data

Frequency (GHz)

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.4

13.0

14.0

15.0

16.0

Sum of Uncertainty

±2.60%

±2.60%

±2.70%

±2.70%

±2.70%

±2.70%

±3.10%

±3.30%

±3.40%

±3.60%

±3.70%

±3.70%

±4.00%

±4.00%

±4.40%

1

Probable Uncertainty

±1.60%

±1.60%

±1.60%

±1.60%

±1.60%

±1.60%

±1.80%

±1.80%

±2.00%

±2.00%

±2.20%

±2.20%

±2.20%

±2.50%

±2.50%

2

17.0

18.0

1. Includes uncertainty of reference standard and transfer uncertainties.
Directly traceable to NBS.

2. Square root of the sum of the squares of the individual uncertainties
(RSS).

±5.20%

±5.10%

±3.20%

±3.20%

Input Impedance: 50 ohms

Operating Resistance: 200 ohms, unbalanced

Power Range with Model 432:

1μ

W to 10mW

Maximum Peak Power: 200W

Maximum Average Power: 30mW

Maximum Energy per Pulse: 10W-μs for a PRF ≥1 k H z ;

5W-μs for a PRF <1kHz

Keysight 8478B Thermistor Mount 15

2-

Operation
Specifications

Figure 2-1 SWR Limits

Maximum
Reflection
Coefficient:

10 to 30MHz: 0.273(1.75SWR, 11.3 dB return loss)

30MHz to 100MHz: 0.15 (1.35 SWR, 16.5 dB return loss)

100MHz to 1GHz: 0.048 (1.1 SWR, 26.4 dB return loss)

1 to 12.4GHz: 0.15 (1.35 SWR, 16.5 dB return loss)

12.4 to 18GHz: 0.230 (1.6 SWR, 12.8 dB return loss)

Elements: Thermally balanced thermistor assembly. Thermistor

assembly is field adjustable so that full zero-set capability can
be restored in the event of inadvertent overload.

RF Connector: Stainless steel type N male (APC-7 also available- see Option

11 below).

Output Connector: Mates with power meter cable (operates directly with 432).

Weight: Net 140g (5 oz).

Option 11: 8478B Thermistor Mount supplied with APC-7 RF connector.

16 Keysight 8478B Thermistor Mount

Operation
Specifications

Maximum Input

The Model 8478B/431 and 8478B/432 combinations respond to the
average RF power applied. The maximum signal applied to the thermistor
mount should not exceed the limitations for 1) average power, 2) pulse
energy, and 3) peak pulse power. Excessive input can permanently
damage the Model 8478B by altering the match between the RF and
compensation thermistors (resulting in excessive drift or zero shift) or
cause error in indicated power.

Average Power

UNDER NO CIRCUMSTANCES APPLY MORE THAN 30mW AVERAGE
POWER TO THE MOUNT. The 8478B/431 and 8478B/432 combinations
can measure average power up to 10mW (ranges 1µ W to 10mW). To
measure power in excess of 10mW, insert a calibrated directional coupler
such as one of the Model 790 series or one of the 8491 series coaxial
attenuators between the mount and the source.

Pulse Energy and Peak Power for 8478B/432 Combination

For pulses shorter than 250µs, energy per pulse must not exceed 10 W-µs
and peak power should never exceed 200 watts. (For example, a 40mW,
250µs pulse contains 10 W-µs of energy.) Pulses longer than 250µs are
allowed to contain more energy but peak power must not exceed 200
watts. Figure 2-2 and Figure 2-3 interpret these limits in graphical form.
(For lack of space, the mount nameplate lists only a 5 W-µs limit, a rating
which applies to the 8478B/432A combination.)

Pulse Energy and Peak Power for 8478B/431 Combination

The limitations of this combination are basically the same as the 8478B/432
with the exception that at pulse repetition rates less than 1kHz, energy per
pulse must not exceed 5 W-µ and peak power must not exceed 10mW. These
limits are also interpreted in Figure 2-2 and Figure 2-3.

Keysight 8478B Thermistor Mount 17

2-

Operation
Specifications

Figure 2-2 Maximum Power Meter Reading vs PRF for Pulses Shorter than 250µs

Figure 2-3 Maximum Power Meter Reading vs Duty Cycle for Pulses Longer than 250µs

Square-wave modulation is a special case of pulse modulation, and maximum
power meter reading versus square-wave frequency is illustrated in Figure 2-4.
This figure also holds for sinewave modulation.

Figure 2-4 Maximum Power Meter Reading vs Square and Sine-Wave Frequency

18 Keysight 8478B Thermistor Mount

Drift Precaution

Operation
Drift Precaution

In the discussions above, the primary consideration is maximum power or
energy. However; for modulation frequencies less than 100 Hz, the low
repetition frequency itself causes errors in indicated power. These errors may
be as large as two percent regardless of range or reading.

When RF is switched by pulse-gating (coaxial solid state switches),
consideration must be given to the RF energy contained in the switching pulse
itself. This energy must be added to actual RF pulse power when estimating
the RF power dissipated in the thermistor mount. PIN diode modulators of
Model 8741A/8716A Modulators and 8614A/8616A Signal Generators,
however, are not subject to this consideration because output filtering
prevents transmission of modulating signals.

Thermistors are inherently temperature sensitive devices. A cold thermistor
mount connected to a warm piece of equipment, or vice versa, produces rapid
drift. FOR MINIMUM DRIFT on sensitive ranges, make sure that the mount and
the equipment connected to it are at nearly the same temperature before
making a measurement.

Let the power sensor warm up at least 30 min before perform COARSE and
FINE ZERO.

Operation with 431A/B/C or 430 Power Meters

If the 8478B is used with a 430 Power Meter, a Model 11528A Adapter is
required.

Because the mount is unbalanced, a large amount of 10kHz audio bias signal
may be coupled from the power meter to the RF source output. The RF source
10kHz output impedance forms a parallel circuit shunt across one of the
detection thermistor elements. If the RF source presents a 10kHz impedance of
15k ohms or greater, the audio bias voltage appearing at the RF input
connection is typically 1.3 Vrms. For an RF source 10kHz impedance of 50
ohms, the audio bias voltage is greatly reduced to typically 5 mVrms: The
presence of a large 10 kHz audio bias voltage at the RF source output may
affect solid state RF sources and RF voltmeter measurements. To minimize or
eliminate these effects, use a high-pass filter at the RF source output.

A variation in 10kHz impedance at the RF input connection affects the power
meter RF detection bridge circuit. This causes a shift in the power meter zero
setting. Refer to the following section for the proper power meter zero
procedure.

Keysight 8478B Thermistor Mount 19

2-

Operation
Zero Set

Zero Set

It is necessary to electrically zero-set the Power Meter before making a power
measurement. To preserve the same zero reference through the measurement,
maintain the same thermal environment when RF power is applied.
Recommended setups for 430 and 431 zero-settings are presented in

“Unbalanced Operation with Model 431A/B/C and 430 Power Meters” and
“Balanced Operation with Model 431C Power Meter”. The recommended

setup for zero-set in the 432 is shown in “8478B/432”.

RF Power Turned Off for Zero-Set

There is minimum zero drift when the zero is set with the RF system connected
to the thermistor mount and the RF power switch off or greatly attenuated by
the generator attenuator. After allowing time for the mount to stabilize
thoroughly, follow zero-set procedures in the Power Meter manual.

Unbalanced Operation with Model 431A/B/C and 430 Power Meters

When the RF source presents a high 10kHz output impedance of 100k ohms or
greater, the power meter may be zeroed with the 8478B disconnected from the
RF source and unterminated as explained in the previous section. If the RF
source presents a low 10kHz impedance of 1k ohm or less, a zero setting made
with the 8478B disconnected from the RF source and unterminated will not be
the proper zero setting for power measurement. This error can be eliminated by
terminating the 8478B in an impedance that approximates the RF source
impedance at 10kHz while zeroing the power meter. For example, if the RF
source 10kHz impedance is 50 ohms, terminate the RF input connection to the
8478B with a 50 ohm resistor.

Balanced Operation with Model 431C Power Meter

When using a balanced mount, if it is inconvenient to turn off RF power in the
RF source, connect the 8478B to the RF source and set 431C Power Meter
RANGE switch to obtain an approximate midscale reading. When the reading
does not drift, disconnect the 8478B from the source, zero the power meter,
and immediately reconnect the mount to the RF source for the power
measurement.

8478B/432

When it is inconvenient to turn the RF power off while using the 8478B/ 432
combination simply remove the mount from the source, and using the COARSE
and FINE ZERO, zero the 432.

20 Keysight 8478B Thermistor Mount

Operation

PdcSubstituted

P

wave

Incident

----------------------------------=

PdcSubstituted

P

wave

Dissipated

-----------------------------------------

Mount Calibration

Mount Calibration

The calibration points imprinted on the label of each 8478B allow power
measurements to be made with increased accuracy. Values of Calibration
Factor and Effective Efficiency are given at seven frequencies between 10MHz
and 18GHz. The mounts are tested on a swept-frequency basis to assure
accurate interpolation between calibration points. Calibration Factor and
Effective Efficiency values are traceable to the National Bureau of Standards to
the extent allowed by the Bureau's calibration facilities.

Calibration Factor

Calibration Factor is the ratio of substituted audio or dc power in a thermistor
mount to the microwave RF power incident upon the mount.

Calibration Factor

Calibration Factor is a figure of merit assigned to a thermistor mount to correct
for the following sources of error:

1. RF reflected by the mount due to mismatch.

2. RF loss caused by absorption within the mount but not in the detection
thermistor elements.

3. dc-to-microwave power substitution error.

Calibration Factor is applied as a correction factor to all measurements made
without a tuner. When these factors and thermoelectric effect (refer to

“Thermoelectric Effect Error Correction for 8478B/431 Combination” on
page 23) are taken into consideration, the power indicated is the power that

would be delivered by the RF source to the characteristic impedance of the
transmission line. The total SWR in the transmission line determines a region of
uncertainty about the measured power. This subject is discussed in Application
Note 64-1, available from any Keysight Sales and Service office.

Effective Efficiency

Effective Efficiency is the ratio of substituted audio or dc power in a thermistor
mount to the microwave RF power dissipated within the mount.

Keysight 8478B Thermistor Mount 21

Effective Efficiency

Effective Efficiency corrects for power absorbed in parts of the mount other
than the detection thermistor elements and dc-to-microwave power
substitution error in the thermistor mount. Effective Efficiency is applied as a

2-

Operation
Calibration Data Application

correction factor when a tuner is used to match the thermistor mount to the
transmission line or RF source. In this case, all of the RF power incident upon
the mount is absorbed in the mount. Since all power is absorbed in the mount,
measurement uncertainty due to mount SWR is eliminated; however, losses in
the tuner must be considered.

Calibration Data Application

When the 8478B is used with the Model 431 or 432 Power Meters, Calibration
Factor or Effective Efficiency corrections can be made by setting a front panel
switch. With the proper setting, the 431 or 432 compensates for the
Calibration Factor or Effective Efficiency in the 8478B. If the 8478B is used with
a power meter other than the 431 or 432, Calibration Factor or Effective
Efficiency corrections can be made by dividing the measured power by the
Calibration Factor or Effective Efficiency value respectively.

22 Keysight 8478B Thermistor Mount

Operation
Thermoelectric Effect

Thermoelectric Effect

When using 431 Power Meters, thermoelectric errors must be taken into
consideration. Mount calibration uncertainties given in Table 2-1 on page 15
include inaccuracies caused by thermoelectric effect error. Calibration Factor
uncertainty of ±1.5% and Effective Efficiency uncertainty of ±2.5% can be
maintained on the three lowest power ranges of the Model 431 series Power
Meters by correcting for the measurement error introduced by thermoelectric
effect. An error correction procedure is given in “Thermoelectric Effect Error

Correction for 8478B/431 Combination”.

A mild thermocouple exists at each point of contact where the connecting
wires join to the thermistor elements. Each thermocouple creates a dc voltage.
Thus, two thermocouple voltages of opposite relative polarity are formed, one
at each junction to each thermistor element.

Ideally, each thermocouple voltage would be equal in magnitude so that they
cancel with no resultant effect on the accuracy of power measurement. In
practice, however, each point of contact does not have identical thermocouple
characteristics, and in addition, the temperatures at each junction may not be
the same. These differences cause an incomplete cancellation of the
thermoelectric voltages, resulting in a voltage that causes a thermoelectric
effect error. The magnitude of the error is important when making dc
substitution measurements on the 0.1mW, 0.03mW, and 0.01mW ranges with
one of the Model 431 series Power Meters. On other ranges, the effect is
negligible. Maximum error introduced by thermoelectric effect is about 0.3µW
and is typically 0.1µW on the 0.01mW range. Refer to “Specifications” on

page 15.

Thermoelectric Effect Error Correction for 8478B/431 Combination

Use the following technique to correct for thermoelectric effect error.

1. Measure power.

2. Connect a HP Model 8402B Power Meter Calibrator to the power meter DC
CALIBRATION AND SUBSTITUTION connector.

3. Zero and null power meter.

4. By dc substitution (refer to procedure in 431 Manual), duplicate power
measurement made in step 1. Calculate and record substituted power as P

5. Reverse connection polarity between the calibrator and power meter.

6. Re-zero and re-null power meter, if necessary.

7. By dc substitution, duplicate lower measurement made in step 1. Calculate
and record substituted power as P2.

1.

Keysight 8478B Thermistor Mount 23

2-

Power

P1P2+

2

---------------=

Operation
Thermoelectric Effect

8. Calculate arithmetic mean of the two substitution powers P1 and P2. This
mean power includes a correction for thermoelectric effect error.

Thermoelectric Error for 8478B/432 Combination

The thermoelectric errors present in the 431 are minimized in the 432 since the
thermoelectric voltage is negligible compared with the dc voltage used to bias
the thermistor bridges.

24 Keysight 8478B Thermistor Mount

Keysight 8478B Thermistor Mount

Operating and Service Manual

3 Operating Principles

General Operation 26

This chapter contains information about operating principles and general
operation of the Keysight 8478B Thermistor Mount.

25

3-

Operating Principles
General Operation

General Operation

Two matched pairs of thermistor elements are used in the 84 78B. Each pair is
connected in series and the two pairs are mounted in a common thermal
conducting block. The thermistor pairs are used in the bridges of the power
meter. One pair, the detection thermistors, is used as an arm of the RF
detection bridge. The other pair, the compensation thermistors, is used as an
arm of the compensation and metering bridge.

Operation with 432 Power Meter

With the 8478B attached to the 432 Power Meter the detection thermistors are
part of the RF bridge and the compensation thermistors are part of the
compensation bridge. Since the two pairs of thermistors show the same
thermal environment, any change in temperature which affects the RF bridge
simultaneously affects the metering bridge; this allows the power meter circuit
to compensate for changes in temperature and thus minimize drift.

During operation sufficient amounts of dc current are supplied from 432 Power
Meter to heat the thermistors until their resistances are reduced to
approximately 2000 per series pair. Capacitor C1 is practically a short to RF.
This causes “D” to appear series connected to the dc bridge, parallel
connected to RF. In this manner, “D” appears to the dc bridge in the 432 Power
Meter as a 2000 resistance that terminates the coaxial cable into 50Ω.
Capacitor C1 blocks any dc and audio power that may be present in the
incoming signal and passes only RF power.

Operation with 431 Power Meter

The RF detection bridge balance is affected by RF power input to the 8478B,
and the bridge is balanced by the application of 10kHz audio bias power. The
compensation and metering bridge is indirectly, but equally affected, by the
application of RF power. Deviation from a near-balance condition is caused by
an equal change in the 10kHz audio bias power to the compensation
thermistor pair, as initiated by the RF detection bridge. The compensation and
metering bridge is returned to near-balance by the application of dc power.

During 8478B/431 operation, sufficient amounts of dc and 10kHz bias currents
are supplied from the 431 Power Meter to heat the thermistors until their
resistances are reduced to approximately 2000 per series pair. Capacitor C3
offers high impedance to 10kHz, but is practically a short to RF. This causes
“D” to appear series connected to 10kHz, but parallel connected to RF. In this
manner, “D” appears to the audio bridge of the 431 Power Meter as a 2000
resistance, but terminates the coaxial cable in 50Ω. Capacitor C1 blocks any dc
and audio power that may be present in the incoming signal, and passes only
RF power.

26 Keysight 8478B Thermistor Mount

Operating Principles
General Operation

432 Power Detection

Under normal operation, the total power applied to heat thermistor pair “D”
(see Figure 3-1) consists of:

1. RF signal

2. heat from the environment

3. dc bias

The total power supplied to heat thermistor “C” consists of:

1. dc bias

2. heat from the same environment

As “D” and “C” are matched thermally, the total amounts of heat applied to
reduce their series resistance equally must be equal.

Figure 3-1 8478B Connected to a 432A Power Meter

Keysight 8478B Thermistor Mount 27

3-

Operating Principles
General Operation

431 Power Meter Detector

Under normal operation, the total power supplied to heat thermistor pair “D”
(see Figure 3-2) consists of:

1. RF signal

2. 10 kHz bias

3. heat from the environment

The total power supplied to heat thermistor pair “C” consists of:

1. dc bias

2. an equal amount of 10kHz bias

3. heat from the same environment

As “D” and “C” are matched thermally, the total amounts of heat applied to
reduce their series resistance equally must be equal.

Figure 3-2 8478B Connected to a 431C Power Meter

28 Keysight 8478B Thermistor Mount

Keysight 8478B Thermistor Mount

Operating and Service Manual

4 Maintenance

Mechanical Shock 30
Performance Tests 32
Troubleshooting 37
Thermistor Compensation 38
Repair and Recalibration 42

This chapter contains information about maintenance and troubleshooting of
the Keysight 8478B Thermistor Mount.

29

4-

Maintenance
Mechanical Shock

Mechanical Shock

The Model 8478B is a precision instrument. A void dropping or other
mechanical shocks. Such shocks destroy the resistive match between
thermistor elements, or otherwise degrade performance.

Test equipment and accessories required to perform maintenance are listed in

Table 4-1. Equipment other than recommended models can be used provided

the critical specifications are satisfied.

The following procedures apply to the 8478B/ 432 combination. The same
procedures can be used for the 431 except that the COARSE ZERO and
FINE ZERO controls are replaced by the ZERO/VERNIER control.

Table 4-1 Recommended Test Equipment

Instrument
Type

Sweep
Oscillator

SWR Meter Sensitivity: 0.15μV for full scale deflection

Critical Specifications Recommended

HP Model

Accuracy: ± 1% full scale for all RF Units

Leveling Capabilities

Frequency Range: 8GHz to 18GHz

8690A,

8694A,

8695A

415E

Accuracy: ±0.05 dB/10 dB step

Range: 70 dB in 10 dB steps

Directional
Detector

Directional
Coupler

Frequency Range: 8.0 to 12.4GHz

Maximum SWR: 1.25:1

Frequency Range: 12.4 to 18GHz 10 dB Coupler

SWR: <1.05:1

789C

P752C

Carriage Accepts HP 816A Slotted Line 809C

Slotted Line Frequency Range: 8 to 18GHz

816A

Impedance: 50 ohms ±0.2 ohms

SWR: <1.06:1, 8 to 18GHz

Probe Frequency Range: 8 to 18GHz 447B

Passband

Passband Frequency: 12.4 to 18GHz P362A

Filter

Crystal

Frequency Range: 12.4 to 18GHz P424A

Detector

30 Keysight 8478B Thermistor Mount

Maintenance
Mechanical Shock

Table 4-1 Recommended Test Equipment

Instrument
Type

Waveguide to
Coax Adapter

Power Meter Power Range: 10mW

Critical Specifications Recommended

HP Model

Frequency Range: 12.4 to 18GHz

P281B

Connector - Type N

432A

Accuracy: ± 1% of full scale

Digital
Voltmeter

Input Impedance: 10 Megohm

Resolution: 4 significant digits

3466A

Accuracy: ±0.05%

Power Supply Output Voltage: 29 Vdc 6217A

Cables 1.Coax-Type N connectors

2. BNC-BNC - male connectors

11500A

10502A

Battery Voltage +2.0 to 3.1 Vdc See “Thermistor

Resistive Match
Test”

Resistor 2.2K ohm 5% 0698-4262

Keysight 8478B Thermistor Mount 31

4-

Maintenance
Performance Tests

Performance Tests

SWR Measurement, 8GHz

SPECIFICATION: SWR at 8GHz = <1.35:1

DESCRIPTION: SWR measurement using standard SWR measurement

techniques.

Figure 4-1 SWR Measurement Test, 8GHz

Procedure:

1. Connect the test equipment as shown in Figure 4-1. Make sure all
connections are secured tightly.

2. Set the instrument controls as follows:

8690B/8692A

SWEEP SELECTOR: CW

FUNCTION: START/STOP

ALC: IN

AMPLITUDE MOD: INT SQ WAVE

START/CW: 8GHz

POWER LEVEL: Adjust to maximum with the UNLEVELED light

off

32 Keysight 8478B Thermistor Mount

Maintenance
Performance Tests

415E

INPUT: XTAL IMPED - HIGH

RANGE-DB/EXPAND: 30/NORM

GAIN /VERNIER: Centered

432

MOUNT RESISTANCE: 200 ohms

RANGE: 10mW

3. Adjust the HP 8690B Sweep Oscillator INT SQ WAVE FREQ for a maximum
reading on the HP 415E SWR meter.

4. Adjust the HP 447B Probe penetration for a half scale reading on the SWR
meter.

5. Move the HP 809C Carriage adjustment for a maximum reading on the
SWR meter.

6. Use the 415E GAIN/VERNIER controls to set the SWR meter reading to 1.0
SWR on the 415E meter.

7. Move the 415E RANGE-DB/EXPAND switch to 0. Adjust the GAIN/VERNIER
controls for a 1.0 SWR reading.

8. Move the 809C carriage adjustment for a minimum SWR reading on the
415E. The SWR at 8GHz should be less than 1.35:1.

HP 415E (8GHz)_________<1.35:1

9. Repeat steps 1 through 8 to determine the SWR at 12.4GHz. The SWR at

12.4GHz should be less than 1.35:1.

HP 415E (12.4 GHz) _________<1.35:1

Keysight 8478B Thermistor Mount 33

4-

Maintenance
Performance Tests

SWR Measurement, 15 and 18GHz

SPECIFICATION: SWR at 15 and 18GHz = 1.6:1 maximum

DESCRIPTION: SWR measurement using standard SWR measurement

techniques.

Figure 4-2 SWR Measurement, 15 and 18GHz

Procedure:

1. Replace the RF unit, filter and directional detector in the 12GHz test setup
with the instruments shown in Figure 4-2.

2. Repeat steps 1 through 8 to determine the SWR at 15GHz. The SWR at
15GHz should be 1.6:1 maximum.

HP 415E (15GHz)________l.6:1 maximum

3. Move the 8690B START/CW control to 18GHz. Repeat steps 1 through 8 to
determine the SWR at 18GHz. The SWR should be 1.6:1 maximum.

HP 415E (18GHz)________1.6:1 maximum.

34 Keysight 8478B Thermistor Mount

Maintenance
Performance Tests

Thermistor Resistive Match Test

SPECIFICATION: Thermistor match ±0.5 ohm.

DESCRIPTION: The voltage drop across each thermistor is measured to

check thermistor match.

Figure 4-3 Thermistor Resistive Match Test

EQUIPMENT REQUIRED:

POWER SUPPLY: HP 6217 A Power Supply

DIGITAL VOLTMETER: HP 3466A Digital Voltmeter

BATTERY: See Note

RESISTOR (2.2K ±5%): HP 0698-4262

The small battery connected in series with the DVM is in opposition to the
power supply. The value of this reverse voltage should be selected to
provide voltmeter resolution of 0.001 volt.

Keysight 8478B Thermistor Mount 35

4-

Maintenance
Performance Tests

1. Connect the equipment as shown in Figure 4-3. Set instrument controls as
follows:

6217A

METER RANGE: 30 VDC

VOLTAGE ADJUST: 29VDC

3466A

RANGE: AUTO

2. Connect point A to pin 3 of the thermistor mount jack and point B to pin 4 of
the thermistor mount jack.

3. Record the DVM Reading.
3466A_____________

4. Connect point A to pin 1 of the thermistor mount jack and point B to pin 2 of
the thermistor mount jack.

5. Record the DVM Reading.
3466A_____________

6. Thermistor match (±0.5Ω) is satisfactory if the two readings do not differ by
more than 0.03 volt.
Difference ______________ <0.03 volt

36 Keysight 8478B Thermistor Mount

Maintenance
Troubleshooting

Troubleshooting

Exceeding the CW or pulse power limits of the Model 84 78B Thermistor Mount
may result in damage such that the mount will no longer zero on the power
meter.

Before adjusting the mount in any way, make sure that the mount is the cause
of the problem. An open or short indication, using the performance test or the
check in below means that the mount is not repairable by the procedure
outlined in the following paragraphs. However, the mount may be
nonoperative, but still repairable. Test for this by using the thermistor resistive
match test procedure, or by connecting the mount to a power meter and cable
which are known to be good. A faulty cable will not have continuity through the
respective connector pins, or may have poor contact at the mount connector.
Poor contact will show up as intermittence or a great deal of noise (visible on
the power meter) when the cable is gently flexed near the connector end.

To troubleshoot a damaged mount, proceed as follows:

1. Connect mount to Model 432.

2. Set:

MOUNT RES: 200Ω

RANGE: COARSE ZERO

POWER: ON

3. Rotate COARSE ZERO from one limit to the other.

If meter remains pegged upscale, the thermistor elements have been
damaged. However, it may be possible to re-compensate the thermistors and
return the mount to operation; otherwise they must be replaced. In either case,
the Effective Efficiency and Calibration Factor data on the nameplate are no
longer valid (refer to “Repair and Recalibration”).

If meter remains pegged downscale, measure resistance between pins 1 and 2,
and pins 3 and 4. The resistance should measure between 1000 and 5000
ohms. An open or shorted reading indicates the need for replacement of the
thermistors.

Under no conditions should the mount be required to carry a current
higher than 14mA.

Keysight 8478B Thermistor Mount 37

4-

Maintenance
Thermistor Compensation

Thermistor Compensation

If the resistance reading is satisfactory, it may be possible to re-compensate
the mount, and return it to service. The drift with temperature changes will be
higher because of the damage to the thermistors, but it will be possible to zero
the meter and to make accurate measurements. The Effective Efficiency and
Calibration Factor imprinted on the label will no longer be valid (refer to

“Repair and Recalibration”). There are two adjusting screws which permit

re-compensation within limits.

Figure 4-4 Printed Circuit Board

Refer to Figure 4-5 and proceed as follows:

1. Remove the three screws (A).

2. Slide terminal shield away from instrument.

3. Plug connector J2 into Model 432A.

4. Connect mount to 50Ω load.

5. Set:

MOUNT RES: 200Ω

POWER: ON

If meter is pegged downscale:

1. Set RANGE to COARSE ZERO.

2. Set COARSE ZERO and adjustment to mid range.

38 Keysight 8478B Thermistor Mount

Maintenance
Thermistor Compensation

3. Turn screws (B) clockwise, 1/8 turn alternately.

The compensating screws are in very close proximity to the thermistors
themselves. Thermistor damage can easily occur if the screws are forced
in any way.

If there is a sudden jump in meter indication when advancing either screw,
back off 1/8 turn, and do not advance that screw further. Check resistance
as in “If meter remains pegged downscale, measure resistance between

pins 1 and 2, and pins 3 and 4. The resistance should measure between
1000 and 5000 ohms. An open or shorted reading indicates the need for
replacement of the thermistors.” on page 37. If either screw bottoms, do

not apply force. Thermistor replacement is indicated.

4. When meter pointer rises, trim to zero with each adjusting screw.

5. Replace terminal shield and three screws (A). The instrument is now
operative.

Keysight 8478B Thermistor Mount 39

4-

Maintenance
Thermistor Compensation

Figure 4-5 Thermistor Mount Assembly

40 Keysight 8478B Thermistor Mount

Maintenance
Thermistor Compensation

If meter is pegged upscale:

1. Set RANGE to highest position which will not peg the meter. If meter pegs
on all ranges, set RANGE to 10mW.

2. Turn one of the screws (B) counterclockwise to obtain a meter reading half
that observed in step 2.

3. Turn the other screw (B) counterclockwise to zero the meter. If it is
impossible to zero the meter, replace the thermistors.

4. Set RANGE to COARSE ZERO; set COARSE ZERO adjustment to mid-range.
If necessary, readjust compensation serials to zero the meter.

The compensating screws are in very close proximity to the thermistors
themselves. Thermistor damage can easily occur if the screws are forced
in any way. If there is a sudden jump in meter indication when advancing
either screw, back off 1/8 turn, and do not advance that screw further.
Check resistance as in “If meter remains pegged downscale, measure

resistance between pins 1 and 2, and pins 3 and 4. The resistance should
measure between 1000 and 5000 ohms. An open or shorted reading
indicates the need for replacement of the thermistors.” on page 37. If

either screw bottoms, do not apply force. Thermistor replacement is
indicated.

5. Replace cover and three screws (A). The instrument is now operative.

The three cover screws must be tight (use lock washers) for proper
operation with 432A. If these screws are not tight noisy operation will
occur.

Keysight 8478B Thermistor Mount 41

4-

Maintenance
Repair and Recalibration

Repair and Recalibration

If repair or recalibration of the mount is desired, the instrument may be
returned to Keysight for repair and recalibration, or for recalibration only.
Arrangements can be made with any Keysight Sales and Service office.

42 Keysight 8478B Thermistor Mount

Keysight 8478B
Thermistor Mount

Operation and Service Manual

A Manual Changes

To adapt this manual to your instrument, refer to Table A-1 and make all of the
manual changes listed opposite your instrument serial number. Perform these
changes in the sequence listed.

If your instrument serial number is not listed on page 2 of this manual or in

Table A-1 below, it may be documented in a yellow MANUAL CHANGES

supplement.

Table A-1 Manual Changes by Serial Number

Serial Number or Prefix Make Manual Changes

CHANGE A

Below 1833A C,B,A

1833A C,B

2030A C

1. Change “Operating Resistance:” on page 15 to “200 ohms Balanced”.

2. Replace the section title “Operation with 431A/B/C or 430 Power Meters”

on page 19 to “Unbalanced Operation with 431A/B or 430 Power Meters"

and its first paragraph with following:

If the 8478B is used with a Model 431 Power Meter, a Model 11527 A
Adapter is required. If the 8478B is used with a 430 Power Meter, a Model
11528A Adapter is required. The use of an adapter breaks the balanced
circuit and an unbalanced circuit results. In this unbalanced condition, a
large amount of IO kHz audio bias signal may be coupled from the power
meter to the RF source output.

3. Delete first sentence of “Because the mount is unbalanced, a large amount

of 10kHz audio bias signal may be coupled from the power meter to the RF
source output. The RF source 10kHz output impedance forms a parallel
circuit shunt across one of the detection thermistor elements. If the RF
source presents a 10kHz impedance of 15k ohms or greater, the audio bias
voltage appearing at the RF input connection is typically 1.3 Vrms. For an
RF source 10kHz impedance of 50 ohms, the audio bias voltage is greatly
reduced to typically 5 mVrms: The presence of a large 10 kHz audio bias

Keysight 8478B Operating and Service Manual-43

-

Manual Changes
CHANGE A

voltage at the RF source output may affect solid state RF sources and RF
voltmeter measurements. To minimize or eliminate these effects, use a
high-pass filter at the RF source output.” on page 19.

4. Change the section title of “Unbalanced Operation with Model 431A/B/C

and 430 Power Meters” on page 20 to “8478B with Model 43IA/B and 430

P o w e r M e t e r s ” .
And add the following to the next paragraph, “The Model 11527A or
11528A Adapter is required when operating the 8478B with 43IA/B or 430
Power Meters respectively.”

5. Replace Figure 3-1 and Figure 3-2 with Figure A-2 and Figure A-2
respectively.

Figure A-2 84788 Connected to a 432A Power Meter (P /0 Change A)

- 44 Keysight 8478B Operation and Service Manual

Manual Changes
CHANGE A

Figure A-2 84788 Connected to a 431 C Power Meter (P /0 Change A)

6. Replace Figure 4-4 on page 38 to Figure A-3.

Figure A-3 Printed Circuit Board (P/0 CHANGE A)

Keysight 8478B Operation and Service Manual -45

-

Manual Changes
CHANGE B

CHANGE B

1. Replace Figure 3-1 and Figure 3-2 with Figure A-4 and Figure A-5
respectively.

Figure A-4 84788 Connected to a 432A Power Meter (P/0 Change B)

Figure A-5 84788 Connected to a 431 C Power Meter (P/0 Change B)

- 46 Keysight 8478B Operation and Service Manual

Manual Changes
CHANGE C

6. For Figure 4-4 on page 38, Return C6 as it is shown in the manual (it was
deleted by “CHANGE C”).

CHANGE C

1. Replace Figure 3-1 and Figure 3-2 with Figure A-6 and Figure A-7
respectively.

Figure A-6 8478B Connected to a 432A Power Meter (P /0 Change C)

Keysight 8478B Operation and Service Manual -47

-

Manual Changes
CHANGE C

Figure A-7 84788 Connected to a 431 C Power Meter (P /0 Change C)

2. Replace Figure 4-4 on page 38 to Figure A-8.

Figure A-8 Printed Circuit Board (P/0 Change C)

- 48 Keysight 8478B Operation and Service Manual

This information is subject to change without notice.

© Keysight Technologies 1981-2018

Edition 3, March 2018

*08478-90015*

08478-90015

www.keysight.com