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'Mi' NIST

PUBLICATIONS

United States Department of Commerce

Technology Administration

National Institute of Standaras arc Technclcgy

NIST Technical Note 1357
1
Coaxial Reference Standard for

Microwave Power

Fred R. Clague

Paul G. Voris

Electromagnetic Fields Division

Electronics and Electrical Engineering Laboratory

National Institute of Standards and Technology

325 Broadway

Boulder, Colorado 80303-3328

April 1993

Ntes o»

U.S. DEPARTMENT OF COMMERCE, Ronald H. Brown, Secretary

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Raymond G. Kammer, Acting Director
National Institute of Standards and Technology Technical Note

Natl. Inst. Stand. Technol., Tech. Note 1357, 52 pages (April 1993)

CODEN:NTNOEF

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1992

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
CONTENTS

1. INTRODUCTION 1

1.1 NIST Microwave Power Standards 1

1.2 Bolometer Mount/Microcalorimeter Operation 2

2. DESIGN CONSIDERATIONS and DECISIONS 4

2.

1

Mount Material 4

2.2 Mount Size 5

2.3 Microwave Leakage 5 2.4 Thermistor Bead Assembly 6

2.5 Effective Efficiency 6

3. PERFORMANCE 7

3.

1

Microwave Leakage 7 3.2 Input Reflection Coefficient 7

3.3 Dual Element Error 8 3.4 Mount Settling Time 9

3.5 Effective Efficiency 10

4. FABRICATION and ASSEMBLY 11

4. 1 Mechanical Design and Drawing Reference 11 4.2 Assembly Details 15

4.2. 1 End Cap Assembly Instructions 15 4.2.2 Body Assembly Instructions 16

4.2.3 Connector Assembly Instructions 19

4.2.4 Mount Assembly Instructions 21

4.2.5 Mount Operating Instructions 21

5. ACKNOWLEDGEMENTS 23

6. REFERENCES 23

APPENDIX A. Parts List Al

APPENDIX B. Part Drawings Common to Both Mounts Bl

APPENDIX C. Part Drawings Specific to Type N Mounts CI

APPENDIX D. Part Drawings Specific to APC-7 Mounts Dl

APPENDIX E. Drawings for Special Assembly Tools and Microwave Absorber Fabrication •. . El

APPENDIX F. Operating Manual Fl

111
TRADE NAME and SI UNITS DISCLAIMER

Certain commercial components used in the reference standard are identified in this document in o(der to adequately specify the design. Such use and identification does not imply recommendation or endorsement by

NIST nor does it imply that the identified items are necessarily the best available for the purpose.

The International System of Units (SI) is used except in the dimensioned part drawings found in Appendix B. The shop which made these parts was not equipped to use metric dimensions. Economic resources are not

currently available to convert the drawings to SI units.

IV
COAXIAL REFERENCE STANDARD for MICROWAVE POWER

Fred R. Clague and Paul G. Voris

National Institute of Standards and Technology

Boulder, Colorado 80303

Design and construction details are given for the bolometer (thermistor) mounts used by NIST as working reference standards for microwave power calibrations in coaxial transmission line. The

effective efficiency of these reference standards can be measured directly in the NIST coaxial

microcalorimeters. The standards are then used to calibrate other microwave power sensors. Two

versions are described: one with a Type N connector and one with an APC-7 connector. The

operating frequency range is O.OS to 18 GHz with either connector. Detailed drawings and

performance measurements are included.

Key words: bolometer mount; coaxial thermistor mount; microwave; microwave power

measurement; microwave reference standard; thermistor mount

1. INTRODUCTION

1.1 NIST Microwave Power Standards

The microwave power standards in use at the National Institute of Standards and Technology (NIST) consist of

microcalorimeters and associated reference standards [1-4]. Each power standard is made up of both a microcalorimeter and a reference standard. The reference standards are substitution type bolometric power

detectors.' Commercial bolometer mounts, especially coaxial units, are generally not suitable for use as the

reference standard. While they have been used by NIST in the past, the resulting calibration uncertainties were

higher because of it.

To meet the need in the microwave community for lower calibration uncertainty, a reference standard designed for use with the microcalorimeter is required. This technical note describes two coaxial bolometer mounts that have

features giving optimum performance with the microcalorimeter. Figure 1 . 1 shows the coaxial microcalorimeter

and the Type N thermistor mount used as the reference standard. Design and construction details for the coaxial

microcalorimeter may be found in reference [5]. This reference and those noted previously all include detailed

descriptions of the microcalorimeter and bolometer mount operation. However, for convenience a brief summary

follows.

'These detectors are generally called bolometer mounts or simply, mounts. In this document, the terms

'reference standard," "bolometer mount," and "mount" are used interchangeably.

1
1.2 Bolometa* Mount/Microcaloruneter Operation

The bolometric power detector uses a heat sensitive resistor

(bolometer) which terminates the transmission line and

absorbs the microwave energy. Two types of bolometers are

used: a platinum wire with a (msitive temperature coefficient

called a barretter, and a thermistor bead with a negative

temperature coefficient. The detectors are biased by an

external source of dc current (power meter) to an operating

resistance that produces a match with the characteristic impedance of the transmission line. Coaxial mounts typically use two bolometer elements which are connected in series for

the dc bias, but are in parallel for the rf. Thus, to match the 50 Q characteristic impedance of a coaxial transmission line,

the pair is maintained at a series resistance of 200 0. When

microwave energy is applied to the mount, the dc bias

supplied by the power meter is automatically reduced to maintain a constant operating resistance [6]. If all the microwave energy incident on the mount were absorbed by

the bolometer elements and if the elements were heated

identically by equal amounts of dc and rf power, then the microwave power would be equal to the amount by which the dc power is reduced. This is called a substitution type power

meter, because the rf F>ower replaces a portion of the dc bias

power. The substituted dc power (also called the bolometric

power) is calculated using the equation

Figure 1.1 Microcaiorimeter and coaxial

reference standard.

^* = V^ - K/

(1.1)

where V, is the power meter output voltage (the dc voltage across the bolometer elements) with no rf, Vj is the power meter output voltage with rf, and R^ is the dc operating resistance of the bolometer pair (200 for a coaxial

mount).

The microwave energy incident on a mount is not all absorbed by the bolometer elements. The dielectric and

conductor losses in the input connector, the input transmission line, and the bolometer mounting structure result in

a measurement error characterized by a correction factor called the mount efficiency. This correction is always less than unity. In addition, the bolometer elements are not heated identically by equal amounts of rf and dc power.

This is known as the rf-dc substitution error. The combination of these two effects, which is measured by the microcaiorimeter, is a correction factor defined as the effective efficiency 17,. The rf power absorbed by the mount
is calculated by dividing the substituted dc power by the effective efficiency. The effective efficiency of the mount

is independent of mismatch corrections, which are treated separately at the time of calibration transfer to an unknown mount.

The bolometer elements used in this application are thermistors. Thermistors are rugged and resist burnout in the

event of an rf overload. They are available commercially as a conveniently usable subassembly. Disadvantages

to using thermistors include a continuous drift in the bias current even in a constant temperature environment. Also,

thermistors are not usable in an alternative efficiency measurement technique known as the impedance method [7].

The microcalorimeter essentially measures the temperature rise of the bolometer mount connected to it. In the

coaxial microcalorimeter, the temperature increase of the mount is measured with a thermopile. During the measurement, the microcalorimeter is immersed in a stable temperature-controlled water bath [8, 9] to minimize

the effect of external temperature changes. The measurement determines the following at each frequency of interest:

the power meter and thermopile output voltages (V, and e,) with only dc applied to the mount, and then again (V^

and e^ with both rf and dc applied. The effective efficiency i;, is calculated at each frequency using the equation

1 -

Tl, =« (1.2)

The term ^ is a frequency dependent correction factor for the microcalorimeter-bolometer mount combination. It

is also known as the calorimetric equivalence correction. The imcertainty in the measurement is determined

primarily by the uncertainty in g. The determination of ^ is a major effort that is described in reference [10]. -cq

A typical reference standard calibration is done at qjproximately 125 frequencies from SO MHz to 18

GHz. Even with an automated system, the measurement takes about 40 h. Figure 1.2 shows a

typical thermopile output at a few frequencies. The

value of 7}, for one of the reference standards, measured

at 125 frequencies, is shown in figure 1.3. The

systematic and total uncertainty in the t;, measurement

as a function of frequency is shown in figure 1.4. Details of the automated measurement system and the uncertainty analysis are found in reference [10].

>

109 60 120 ELAPSED "nME. rrwi

180 240

Figure 1.2 Thermopile output versus time for seven frequencies (in GHz).
100

8 X) 15 FREQUENCY. GHz

Figure 1.3 Type N mount effective efficiency

measured at 125 frequencies.

0.5

t- 04

UJO

S 0.3

2

< 0.2

TOTAL UNCCHTAMTY

SYSTEMATIC UNCeRTAMTY

: ^^j.:-^-^^^---^-;

-' . . . ^ ^^ -< 01 r—

0.01 0.1 1 10 30 LOG FREQUENCY. GHz

Figure 1.4 The total and systematic uncertainties

for the Type N coaxial microcalorimeter when measuring the effective efficiency of a NIST Type N mount.

2. DESIGN CONSIDERATIONS and DECISIONS

The features of the bolometer mount described below are both desirable and necessary for the mount to be used as an optimum reference standard. The body of the mount and the internal thermistor bead assembly are both

considered.

2.1 Mount Material

As noted in the introduction, the primary function of the microcalorimeter is to measure the effect of all microwave

energy dissipated in the mount. To best accomplish this there should be minimal thermal resistance between the

heat sources and the measuring thermopile. Thus, the mount should be constructed of material with a high thermal

conductivity and the thermal paths be short as possible. Typical commercial mounts are constructed of nickel-plated or gold-plated brass and might also have stainless steel parts in the thermal path.

The transfer standard should have a high effective efficiency. This means a low rf-loss input transmission line constructed of a high electrical conductivity material with a good surface finish.

To meet these requirements, the mount body is constructed of tellurium copper, while the parts of the mount that involve the input transmission line (the outer conductor) are made of electroformed copper. The electrical

conductivity of copper is nearly 3 times better than brass and 30 times better than stainless steel. The thermal

conductivity is about 2.5 times better than either brass or beryllium copper and 26 times better than stainless steel. The electroformed parts provide a better outer conductor surface. than can be obtained by machining.

The disadvantage of these two materials is that they are softer than beryllium copper or brass. This is more of a

liability for the Type N mount (because of a vulnerable connector outer conductor) than for the APC-7 design. With
careful handling, it is not a major problem with either design. Experience with one of the Type N mounts reveals no visible connector damage after more than 100 connections. All parts of the mount are gold plated to prevent

deterioration of the surface characteristics, primarily thermal emissivity and electrical conductivity.

2.2 Mount Size

Valid measurements of the thermopile output and the power meter voltage cannot be made until the microcalorimeter

and mount are in thermal equilibrium with the water bath, a condition indicated by a stable thermopile output. The

time to reach stability may be lengthy: an average of 50 min per measurement frequency on the commercial mounts

because of their long thermal time constant. A typical calibration at 105 points can take about 90 h. To minimize

the effect of external temperature changes, all commercial mounts are typically massive and seek to thermally isolate

the thermistor bead structures. Such design objectives are the opposite of those desired for use in the

microcalorimeter. An effective way to speed Ihe measurements is to minimize the thermal mass (heat capacity) of

the bolometer mount by reducing the size and to eliminate the thermal isolation.

Both techniques are used in the new mounts. For example, the mass of the new Type N mount is approximately

one-third that of the commercial version previously used (53 g versus 142 g). The average measurement time per frequency for the new design is less than 30 min (see Section 3).

2.3 Microwave Leakage

The rf leakage from the bolometer mount is a first-order source of error in the measurement. The leakage energy, because it is not dissipated in the mount, is not detected by the bolometer elements or by the microcalorimeter

thermopile. Leakage may radiate or conduct through mechanical joints in the mount body, the dc bias leads, or the

rf input connector. Commercial mounts, which are adequate for their intended use, generally do not have low

enough leakage for this application, where errors on the order of 0.01 percent are of concern.

The effort to minimize leakage has focused on rf containment by the mount body and the dc bias circuit. The

shielding is accon^lished by totally enclosing the mount and minimizing any gap that might allow leakage at a mechanical joint. Residual leakage from threaded joints can be further reduced by painting the seam with

conductive epoxy or paint. Because of the thin wall of the mount body, the cap is not threaded. It is designed to be a tight press fit in the body; in fact, a special fixture is needed to remove the cap. A puller tool is described

in Appendix E. Once it is determined that a newly constructed mount is of>erating properly, the cap seam can also be sealed with conductive epoxy or paint.

The internal rf bypass structure consists of a tubular pi-section (a pair of capacitors with a ferrite inductor) low pass

filter with an added external ferrite bead in each of four leads. A cross section of the dc feed-through structure is shown later in figures 4. 1 and 4.2. The dc connection to the thermistor beads is through a miniature connector to allow the mount cap to be removed.
2.4 Thermistor Bead Assembly

As described earlier, the substitution type power meter measures power in terms of a change in the dc bias power.

Uncertainty in the bolometer dc resistance will be reflected as an error in the power calculation. Lead or contact

resistance in the dc bias circuit will generate such an error. The solution to this problem is a four-wire connection

from the bolometer elements to a power meter which uses external sense leads such as the NIST Type IV power

meter (made commercially by several manufacturers). The thermistor bead assembly used in the mount has the

required four-wire connection.

Q>axial bolometer mounts typically use a dual bolometer configuration. The elements are connected in series for

the dc bias and in parallel for the rf. This simplifies the dc bias connection and also provides a good rf match to

the SO Q transmission line. However, if the electrical characteristics of the two elements are not identical, a dc-rf

substitution error in the power measurement results. For thermistor mounts, the error increases in a nonlinear manner with rf power. The error is restricted to coaxial mounts, since in general, waveguide designs use a single

element. The effect can be minimized by proper matching of the element pair. The beads in the assembly used

are matched to 0.05 at 165 °C. The details of the dual-element error are presented in reference [11].

Another performance parameter for the mount, which is a function of the bead assembly, is the input reflection

coefficient. A low reflection coefficient is not necessary for the microcalorimeter measurement, but it is important

for reducing the uncertainty in the calibration transfer and, as a practical matter, for reducing the minimum power

requirement on the microwave source. The thermistor bead structure with its unique four-wire connection is a conunercial product. This greatly simplifies the construction of the mount.

2.5 EfTectiye Efficiency

As noted in Section 2. 1, the effective efficiency should

be high, at least above 90 percent. Another desirable

feature is that 77, be a slow, smoothly varying function

of frequency. Most thermistor mounts display resonances, or sharp narrow dips in 17,. Because 17, is changing very rapidly with frequency at these points,

the random uncertainty is greater, and interpolation

between measured points is not possible. As will be

described in Section 3.5, the resonances can be

suppressed. Figure 2. 1 is a plot of effective efficiency versus frequency for the same mount shown in figure

1.3, but without resonance suppression.

1.00

FREQUENCY. GHz

Figure 2. 1 . Type N moimt effective efficiency before resonance suppression.
3. PERFORMANCE

Material presented in this section reports the actual measured performance of several samples of the Type N mount

only. (At the time of this publication, customer interest in an APC-7 service has not been sufficient to warrant

constructing the mounts or evaluating the calorimeter. The parts, however, are in hand and can be assembled and

evaluated if needed in the future.) These measurements are thought to be typical and thus representative of future

units. The basis of these performance measures was presented earlier in Section 2.

3.1 Microwave Leakage

-40

<

<

UJ

-50 -

-60 -

-70

-80

-90

-100

-110

I I I t ? I III

Detection of microwave leakage is relatively easy; accurate measurement of its magnitude is not. Development of

special techniques and facilities such as the reverberation chamber and the TEM cell make such measurements

potentially possible [12]. A reverberation chamber can be used to measure the energy above about 300 MHz (the

low frequency limit is determined by the size of the

available chamber) that is radiated from the mount and

its connected dc bias cable. Energy that is conducted

from the mount on the connecting dc bias cable can be

measured using a vector voltmeter and a spectrum

analyzer. Measurements on early prototype mounts

show that most of the energy escaping from the mount

is conducted away on the connecting cable, rather than

being radiated. Therefore, measurements were not made in the reverberation chamber.

VECTOR VOLTMETER MEASURMENT

SPECTRUM ANALYZER KCASURKCNT

0.01 Results shown in figure 3.1 were obtained from

measurements on the mount using a vector voltmeter at

the low frequencies and a spectrum analyzer above 1 GHz. The objective was to keep total leakage from

the mount more than 40 dB below the input (less than

0.01 percent of the input). The figure indicates this was achieved.

3.2 Input Reflection Coefficient

As previously indicated, it is desirable for the magnitude of the input reflection coefficient to be small. The measurements made by an automatic vector network analyzer (45 MHz to 18 GHz) and by a six- port network analyzer (10 MHz to 50 MHz) on a

typical Type N mount are shown in figure 3.2. Themagnitude is under 0.1 from about 20 MHz to 16.5

GHz.

0.1 1 LOO FREQUENCY. GHz

Figure 3.1. Microwave leakage in decibels below the

input.

UJo

D

t-2o

<2

0.15

0.10

: : :•

;

''

005

: : ; ^/ ^^ 1 \/ ..——^ V

001 01 1 LOG FREQUENCY. GHz

<0 20

Figure 3.2. Type N mount reflection coefficient.
?i 3.3 Dual Elonent Error

First, if the mount is used at 10 mW, where it was calibrated, there is no error. However, if the mount is used

as a reference standard to calibrate another system at a different power, say 1 mW, then there may well be an

additional uncertainty in the measurement.

.

,

, an >

• •.

'

aoo

.1 • ..•

•• *•"'' '..••.

.

< ... OM 1 •

1' Ami M: WAVEOUnE MOUKT

• AfWaK WAVEOUOe MOUNT

•0.W 1 . . . . •10 10

pciwcn.«m

The only way to determine the magnitude of the dual-element error is by direct measurement. In theory, one

possible measurement method is to connect the coaxial mount to one arm of a nominally equal power splitter (such

as a 3 dB hybrid or a waveguide 'magic tee") and a single element waveguide mount to the other arm. The ratio of the two bolometric powers is determined at 10 mW and again at a randomly selected power between 10 mW and

0.1 mW. The change in the ratios as determined at the two powers is a measure of the dual-element error. The

process is repeated enough times to give a curve showing the nonlinearity as a function of power up to 10 mW.

The test of the procedure is to place identical model

waveguide mounts on each arm of the power splitter to

verify the linearity of the splitter and associated

instrumentation. Figure 3.3 shows results of such a measurement with two identical model waveguide

mounts at 9. 1 GHz. The increased spread of the data

as the p>ower decreases is typical of bolometric

measurements because of the small change in dc power

that occurs at low microwave power.

The result for a commercial coaxial mount compared

with one of the waveguide mounts is shown in figure

3.4. The error is very small at low power and

increases to about 0.035 percent at 10 mW.

Unfortunately, most of the data taken using this technique does not give results comparable to figures 3.3 and 3.4. Considerable time has been put into the

effort to reduce this approach to a reliable measurement

technique. Thus far, it has not been successful. Generally, the results of the power splitter linearity tests have not provided the desired verification, so the comparisons between the coaxial mount and a waveguide mount are not meaningful. The difficulty seems to be that when looking for deviations on the order of 0.01 percent, instrumentation problems such as the inability to locate the ground precisely where it

Figure 3.3. Change in the power ratio of two

waveguide mounts versus power.

aio

0J» -

0J»

-1—I I

I

; .:.'•:- i^WV <

"''"

'

•*

' ^^-.:^-^ ,^^

AMIM: COAXIAL UOUNT

ARM «K WAVEOUnC UOUNT

-10 10 rauEKt

Figure 3.4. Change in the power ratio of a

coaxial mount to a waveguide mount

versus power.
should be in the dc measurement circuit or the effect of stray thermal junctions are of the same order. At best, the comparison between the coaxial and waveguide mounts is in error by the amount of the apparent nonlinearity seen when comparing a waveguide mount to a waveguide mount.

Another way to determine the dual-element error is to measure the effective efficiency as a fiinction of power.

Figure 3.5 shows that measurement on a Type N mount. The significant nonlinearity above about 12 mW is largely

due to the dual-element error. At the lower power levels the measurement uncertainty becomes quite large so the shape of the curve is not necessarily accurate. A line fitted to the measured data between S mW and 12 mW is shown in figure 3.6. Based on this linear fit, the change in efficiency between 10 mW and 1 mW is less than 0.01

percent. This is a better estimate of the dual-element error than the power splitter method provides.

99.5

u.UJ

990 -

Q

ILU.UJ

UJ 98.5 h-

>

98.0

I I I I

I I

f I I I I

I I I I

I

'''*'* 10 POWER. mW

15 20

99.130

POWER. mW

Figure 3.5. Effective efficiency as a function of

power.

Figure 3.6. Linear fit to data of figure 3.5 from 5

to 12 mW.

3.4 Mount Settling Time

In figure 3.7, the upper trace is the output of a crystal detector monitoring a 10 GHz source as the rf is turned on for about 6 ms, and then turned off. The lower

trace is the power meter voltage of the coaxial

thermistor mount as it measures the same output. Note

the rather large "overshoot" excursions that occur for about 2 ms until a steady state is reached. These

excursions may occur because the current distribution in

the thermistor beads changes when rf is applied, so the

heat distribution must also change. It takes a few

milliseconds for a new thermal steady state to be

reached. Thus the measurement of the power meter

voltages should not be made until after the overshoot

1 A 1 —•^ -:--'-- - - •--.... 'V

\i_ 1

1 ; \] : :.:..:„.;

- i-J*** j^,J^ i

\w

^

4 e BAPSEDTIUEnM

10

Figure 3.7. Crystal detector and mount output as rf power is switched on and off. The

source output is 10 mW.
has subsided. The effect decreases with decreasing power and is independent of frequency.

3.5 EfTective EfficiaKy

A plot of the effective efficiency of one of the Type N

mounts was shown in figure 1.3. The efficiency is well

above 90 percent and decreases smoothly with

frequency. Figure 3.8 is a plot of the rj, of a mount

before and after suppression of the resonant behavior

described in Section 2.5. The resonance effect is the

result of microwave leakage past the thermistor beads

into the space that forms a cavity behind the thermistor

bulkhead. The effect can be reduced or even eliminated

by filling the cavity with two layers of magnetic

microwave absorber. The fill material is fastened in place to prevent movement which could change the t;,.

too H

Z

UJ 0.99

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'^ 0.98

(U 0.97 Q

ILlb 096

tu>

0.95 -

94 -

> 1 r- t , T 1 1 1

;^==^i.,^..

- : 1 /Nu

II \i

II V

... "^

: ir

uI

\

1

10 FREQUENCY. GHz15 20

Figure 3.8. Type N mount effective efficiency before

(dashed line) and after resonance

suppression.

10
4. FABRICATION and ASSEMBLY

4.1 Mechanical Design and Drawing Reference

Figure 4. 1 shows a cross section

of the Type N mount with the

parts identified. Figure 4.3 and

4.4A are exploded cross

sectional views that give an ID

designator for each part. The

parts are listed in tables in

appendix A. The items that can

be obtained commercially are

listed in table A. 1 . The supply

sources for these parts are listed

in table A.2. Table A.3

contains the parts that must be

fabricated. The first letter of

the figure number indicates in which appendix the

dimensioned part drawing can be

found. Included in appendix B

is figure B6, the wiring

convention for the dc bias

connector Jl.

DC B I AS

CONNECTOR

PC BOARD

(CONNECTOR

TO FILTER)

LOW PASS F ILTER

MICROWAVE

ABSORBER

FERR I TE BEAD

MINIATURE

CONNECTOR

PC BOARD

(CONNECTOR

HOLDER)

THERMI STOP

ASSEMBLY

BELLOWS CONTACT

AND DC BLOCKING

CAPAC I TOR

TYPE N RF INPUT

CONNECTOR

Figure 4.1. Cross section of the Type N thermistor mount.

11
Figure 4.2 shows a cross section

of the APC-7 mount with the

parts identified. Figure 4.3 and

4.4B are exploded cross

sectional views that give an ID

designator for each part. The

parts are listed in tables in

appendix A. The items that can

be obtained conmiercially are

listed in table A. 1 . The supply

sources for these parts are listed

in table A. 2. Table A.

contains the parts that must be

fabricated. The first letter of

the figure number indicates in which appendix the

dimensioned part drawing can be

found. Included in Appendix B

is figure B6, the wiring

convention for the dc bias

connector J 1 . Note that part D2

may be supplied with part

APCl. However, it cannot be

used because it is not made of

copper.

DC BIAS

CONNECTOR

PC BOARD

(CONNECTOR

TO F ILTER)

LOW PASS F I LTER

MICROWAVE

ABSORBER

FERRITE BEAD

MINI ATURE

CONNECTOR

PC BOARD

(CONNECTOR

HOLDER)

THERMISTOR

ASSEMBLY

BELLOWS CONTACT

AND DC BLOCK I NG

CAPAC I TOR

APC-7 RF INPUT

CONNECTOR

Figure 4.2. Cross section of the APC-7 thermistor mount.

12
PART J

PART Bl

PART PCI

PART LI

PART B2

PART E3

PART E4

PART L2

PART B3

PART J2

PART PC2

PART TBI

imr

I [\\\\M I kWWV

I \///i I W///A rJ'l V///A \YZ77\ A

l/A

I v///y///A

I l/A a

'k ! ra 1 1

1

1

.

1 y<f^(' m/m^

1

1

1 , ^

/

1

1 ^ / 1 '//. /// 1 /

1.,. /

1

1

Figure 4.3. Drawing and part reference for the parts common to both the Type N and the APC-7 thermistor

mount.

13
PART CI

PART C2

PART C3

PART N1

PART BL

PART C4

PART N2

PART N3

Figure 4.4A. Drawing and part reference for the parts specific to the Type N thermistor mount.

PART Dl

PART D2

PART APC1

O PART BL

I^ PART D3

mM

PART AP12

Figure 4.4B. Drawing and part reference for the parts specific to the APC-7 thermistor mount.

14
4.2 Assanbiy Details

The following section describes detailed steps for the assembly of the Type N coax mount. The APC-7 version is

not described separately because its assembly would differ only in minor ways with respect to the connector. The

items in parenthesis are part designations. Assembly of the mount is done in 4 stages. These stages are cap, body,

connector, and final mount assembly. Each stage is made up of several steps.

4.2.1 End Cap Assembly Instructions

The first stage of construction is to assemble the end cap. Refer to appendix A and figure 4.5 during this stage of

construction. The tools, supplies, and parts needed are listed below, followed by the assembly steps.

1. Soldering iron and associated tools

2. Solder, No. 24 S.W.G. 63% Sn/37% Pb

3. Trichloroethane technical

4. Ultrasonic cleaner

5. Deionized water

6. Hot plate

7. Conductive silver paint (S5)

8. Four-conductor miniature connector (Jl)

9. Lx>w pass filter (LI), four each

10. Pc board (PCI)

11. Low pass filter plate (B2)

12. End Cap (Bl)

Step 1. Attach miniature connector to end cap.

a. Heat hot plate to 232°C (450°F).

b. Remove rubber gasket from the miniature connector (Jl).

c. Wrap one loop of solder around the base of the miniature cotmector.

d. Push the connector into the end cap (Bl).

e. Place the end cap on the heated hot plate.

f. After solder flows remove end cap from the hot plate and allow to cool.

Step 2. Solder four low pass filters (LI) to each of the outer diameter holes on the pc board (PCI). Place each

filter so that the flange is facing away from the pc board.

Step 3. Insert the pc board with attached filters into the end cap, aligning the center holes on the pc board with the

four conductors of the miniature connector. The pc board should rest on the inside lower lip of the end

cap.

Step 4. Solder miniature connector leads to pc board.

15
MINIATURE

CONNECTOR

(J1).

END CAP

(B1)

PC BOARD

(PCI)

LOW PASS

FILTERS

(LI)

V//A \V^///AV\A f yyyyyi I VTTA

I A ! A

\i7 \v^

zzzzc DZZI

I

\

(0.35 in)

LOW PASS [zzn FILTER PLATE

(B2)

Figure 4.5. End cap assembly.

Step 5. Clean the inside of the end cap of all flux residue and deposits.

a. Soak the end cap in a trichloroethane ultrasonic bath for at least 15 min.

b. Rinse the end cap in deionized water and allow to air dry.

Step 6. Push filter plate (B2) into end cap until plate rests on the inside upper lip of the end cap.

Step 7. Trim the filter leads to 8.9 nun (0.35 in) from Alter plate.

Step 8. Attach and seal filter plate to end cap and filters with conductive silver paint (S5).

4.2.2 Body Assembly Instructions

The second stage of construction is the assembly of the mount body. Refer to Appendix A and figures 4.6 and 4.7

during this stage of construction. The list of tools, supplies, and parts needed are followed by the assembly steps.

1Soldering iron and associated tools

2. Wrench C, see figure El in Appendix E

3. Solder, No. 24 S.W.G. 63% Sn/37% Pb

16
FERRITE BEAD

(L2) 1—i— 1 i 1—i— i

BODY PART B (B3)

2^

PC SWAGE MOUNT

CONNECTOR

(J2)

PC BOARD (PC2) H

HEAT SHRINKBLE TUBING ;

THERMISTOR BULKHEAD ^^ (TBI)

BODY PART A (CI)

TT

i

THERMISTOR TWIN WIRE OUTPUT

13:

^ ^

H

/

I^^

Figure 4.6. Mount body assembly.

4. Ferrite shielding bead (L2), four each

5. Pc swage mount connector (J2), four each

6. Thermistor bulkhead (TBI)

7. Thermally conductive epoxy (S4)

8. Heat shrinkable tubing, 3/64 in diameter

9. Body part A (CI)

10. Body part B (B3)

17
MICROWAVE ABSORBER

LAYER 2

MICROWAVE ABSORBER

LAYER 1

SECURE MICROWAVE ABSORBER

TO BODY WALL WITH RTV

LAYER 2

LAYER 1

SECTION A-A

'mWi I mAW\

SECTION B-B

Figure 4.7. Molded RTV magnetic absorber parts.

11. Pc board (PC2)

12. Microwave absorbers (E3 and E4; for instructions to make them, see Appendix E)

13. Silicone rubber coating (SI)

Step 1. Solder four pc swage mount connectors (J2) to pc board (PC2).

Step 2. Cover protruding connector ends on imder side of PC board with heat shrinkable tubing.

Step 3. Place the pc board with attached connectors on the thermistor bulkhead (TBI), aligning the pc board with

the two threaded studs.

18
Step 4. Using two # 0-80 nuts, secure the pc board to the thermistor bulkhead studs.

Step S. Solder each thermistor lead wire to the bottom of its corresponding connector; see figure 4.6.

Step 6. Place thermistor bulkhead in body part A (CI).

Step 7. Using wrench C tighten body part B (B3) to body part A.

Step 8. Inspect the assembly under a microscope to see that the thermistor bulkhead is seated tightly against the outer conductor of body part A.

Step 9. Attach a ferrite bead (L2) with thermally conductive epoxy to each of the pc swage mount connecters.

Stq) 10. Place two microwave absorbers into mount body as shown in figure 4.7. Secure each of the

absorbers to the mount body wall with a small amount of RTV (SI). Let RTV cure for 24 h before final assembly.

4.2.3 Connector Assonbly Instructions

The third stage of construction is the assembly of the connector. Refer to Appendix A and figure 4.8 during this stage of construction. The tools, supplies, and parts needed are listed below, followed by the assembly steps.

1. Two collets, both sized to hold the 3.040 mm (0.1197 in) center conductor, with holders

(3.1 mm type D is suggested)

2. Wrenches A and B, see figure El in Appendix E

3. Type N male pin (N3)

4. Type N center conductor support bead (N2)

5. Type N conductor shell and coupling ring (Nl)

6. Connector body (C2)

7. Coupling nut (C3)

8. Center conductor extension (C4)

Step 1 . Insert the threaded end of the Type N male pin (N3) through the center of the center conductor support

bead(N2).

Step 2. Attach the center conductor extension (C4) to the threaded end of the Type N male pin. Orientate the

center conductor extension so that the thread relief is towards the center conductor support bead. Apply

sufficient torque to insure that the thread will not loosen by using the collets, either manually or in a lathe. Exercise care to not mar the center conductor surface or strip the threads.

Step 3. Place the pin with support bead and extension into the connector body (C2) making sure the support bead

is properly seated.

19
CENTER CONDUCTOR

EXTENSION

(CO

CENTER CONDUCTOR

SUPPORT BEAD

-THREAD RELIEF

(N2)

TYPE N MALE PIN

(N3)

CONNECTOR BODY

(B2)

CONNECTOR

COUPLING RING

COUPLING NUT

(C3)

CONNECTOR

SHELL

(N1)

208

211

in)

in)

Figure 4.8. Connector assembly.

20
Step 4. Slip the connector coupling ring (Nl) onto the coupling nut (C3) so that it rests in the coupling nut groove.

Step 5. Thread the connector (C2) body into the coupling nut.

Step 6. Push the connector shell (Nl) over the coupling nut and ring assembly.

Step 7. Using wrenches A and B tighten assembly.

4.2.4 Mount Assembly Instructions

The final stage of construction is the assembly of the mount utilizing the cap, body, and connector assemblies.

Refer to Appendix A and figure 4.9 during this stage of construction. The tools, supplies, and parts needed are

listed below, followed by the assembly steps.

1. Cap assembly

2. Body assembly

3. Connector assembly

4. Bellows contact and dc blocking capacitor (BL)

5. Wrenches B and C, see figure El in Appendix E

6. Mount assembly tool, see figure E2 in Appendix E

Step 1 . Place bellows on connector assembly center conductor extension.

Step 2. Tighten body to connector assembly using wrenches B and C; make sure to keep the bellows properly

seated.

Step 3. Press the cap into the body assembly using the mount assembly tool (figure E2), keeping the notch on the

miniature connector aligned with either one of the shorted internal connector pair as indicated in figure 4.9. Use an ohmmeter to identify the shorted pair.

Step 4. Check the Type N connector dimensions; the measurements should be between 5.28 mm (0.208 in) and

5.36 mm (0.211 in). See detail in figure 4.8.

4.2.5 Mount Operating Instructions

A copy of the mount operating manual is found in Appendix F. The Type N version of the mount has been

designated a Model CN and is so identified in the operating manual.

21
CAP ASSEMBLY

w^

Y^ '&r'frr>^

\i7

I SHORTED PAIR

I

M I CROWAVE

ABSORBER

\ \\m \^

1

)

/,

BODY

ASSEMBLY

BELLOWS CONTACT

AND DC BLOCKING

CAPACITOR

(BL)

CONNECTOR

ASSEMBLY

Figure 4.9. Final mount assembly.

22
5. ACKNOWLEDGEMENTS

The authors acknowledge the helpfulness of the early work and ideas of Morris E. Harvey upon which this effort

is based. Thanks also to Neil T. Larsen for his support and many helpful discussions and suggestions. This work

was partially funded by the Calibration Coordination Group of the Department of Defense.

6. REFERENCES

[I] MacPherson, A.C.; Kerns, D.M. A microwave microcalorimeter. Rev. Sci. Instrum. 26(1): 27-33; 1955

January.

[2] Engen, G.F. A refined x-band microwave microcalorimeter. J. Res. Nat. Bur. Stand. (U.S.). 63C(1): 77-82;

1959 July-September.

[3] Harvey, M.E. WR 15 microwave calorimeter and bolometer unit. Nat. Bur. Stand. (U.S.) Tech. Note 618;

1972 May. 33 p.

[4] Weidman, M.P.; Hudson, P. A. WR 10 millimeter wave microcalorimeter. Nat. Bur. Stand. (U.S.) Tech. Note

1044; 198IJune. 11 p.

[5] Clague, F.R. 7 mm coaxial microwave microcalorimeter. To be published as Natl. Inst. Stand. Technol.

Tech. Note 1358.

[6] Larsen, N.T. A new self-balancing dc-substitution rf power meter. IEEE Trans. Instrum. Meas. IM-25: 343-

347; 1976 December.

[7] Engen, G.F. A bolometer mount efficiency measurement technique. J. Res. Nat. Bur. Stand. (U.S.). 65C(2):

113-124; 1961 April-June.

[8] Larsen, N.T. 50 microdegree temperature controller. Rev. Sci. Instrum. 39(1): 1-12; 1968 January.

[9] Harvey, M.E. Precision temperature-controlled water bath. Rev. Sci. Instrum. 39(1): 13-18; 1968 January.

[10] Clague, F.R. A calibration service for coaxial microwave power reference standards. To be published as Natl. Inst. Stand. Technol. Tech. Note.

[II] Engen, G.F. A dc-rf substitution error in dual-element bolometer mounts. IEEE Trans. Instrum. Meas. IM-13:

58-64; 1964 June-September.

[12] Crawford, M.L.; Koepke, G.H. Design, evaluation, and use of a reverberation chamber for performing

electromagnetic susceptibility/vulnerability measurements. Nat. Bur. Stand. (U.S.) Tech. Note 1092; 1986 April.

146 p.

23
APPENDIX A. Parts List

These tables identify the parts and supplies that can be obtained commercially and those parts that must be

fabricated.

Table A.l. Commercial parts list

Part ID DcKription No./ mount Pan No, Manufacturer

APCl 7 mm connector auembly 1 No. 131-91051, 7 mm connector for air line Amphenol Connector Division

BL DC blocking capacitor with

bellowi

1 No. 08478-6001S, blocking capacitor Hewlett-Packard Con^iany

Jl 4-conductor miniature connector 1 No. DR-4S-4PC, printed circuit recepUcle (mating connector: DP-4S-1

straight plug) Microtech. Inc. Boothwyn. PA 19061. a15) 4S9-3566

J2 Single-conductor miniaUire connector4 No. MC72, pc swage mount SPC Technology

(Newark caulog No. 46N7630)

LI Low past filter 4 No. 1234-0000, pi section solder mount single muRata/Erie North America, Inc. (Newark caulog No. 90F2245)

L2 Ferrite bead 4 No. 52004-4S2, shielding bead

Ferroxcube, Phillips ComponenU, Discrete ProducU Div.

Nl Type N connector coupling ring 1 No. 8812S2, snap ring No. 881251. coupling nut Maury Microwave Corp. Onurio. CA 91746. (714) 987-4715

N2 Type N center conductor support bead1 No. S04O-O306, insulator, rf connector

Hewlett-Packard Co.

N3 Type N male pin 1 No. 1250-0917. rfconuct

Hewlen-Packard Co.

TBI Thermistor bulkhead 1 Model 8478B option KOI. thermistor bulkhead Hewlen-Packard Co.

Table A. 2. Supplies list

Supply ID Description Part No, Manufacturer |

SI Silicon nibber 3140 RTV Coating, Dow Coming

S2 Low viscosity silicon rubber RTV 61 5 A, Silicone Rubber Compound

GE Silicones, General Electric Co., Waterford. NY 12188 (518)237-3330

S3 Carbonyl iron powder Micropowder Iron. Grade S-5641 (caibonyl iron) International Specialty ProducU, 1361 Alps Rd., Wayne, NJ 07470,

(800) 622-4423

S4 Thermally conductive epoxy adhesive

(electrically insulating)

Thermalbond 4952

Thermalloy, Inc, PO Box 810839. DalUs, TX 75381-0839 a14) 243-4321

Al
Table A. 2. Supplies list (continued)

S5 Conductive silver paint Type 22-202, GC Electxx>nic« (Newark cauiog No. 0OZ869)

Table A. 3. Fabricated parts list

Part ID Description No./

mount

Figure

number

Bl End cap 1 Bl

B2 Low pass filter plate 1 B2

B3 Body part B 1 B3

PCI Connector/filter printed circuit board 1 B4

PC2 Thermistor bulkhead printed circuit board 1 B5

CI Body part A (Type N) 1 CI

C2 Connector body (Type N) 1 C2

C3 Coupling nut mounting ring (Type N) 1 C3

C4 Center conductor extension (Type N) 1 C4

Dl Body part A (APC-7) 1 DI

D2 Connector body (APC-7) 1 D2

D3 Center conductor extension (APC-7) 1 D3

El Special assembly wrench A, B and C - El

E2 Mount cap puller - E2

E3 Microwave absorber 1 E3

E4 Microwave absorber 1 E3

The material, plating, and other items specified on the drawing must be strictly complied with in the fabrication of

the part. The mount cannot be used as a transfer standard that is calibrated directly in the microcalorimeter if they

are not. The evaluation and error analysis of the microcalorimeter are not valid imless the mount to be used as the

transfer standard is made exactly to the NIST design as specified by the drawings.

A2
APPENDIX B. Part Drawings Common to Both Mounts

roO OOOO

OO >- + 1 — Q

O lO zm u3 U. O - 1^ i-Z — o o

U.O2

(JO

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1

(3) lO in

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m m

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TSl OO JO.<o

00 ia ^

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- Kl CD O

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X

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o

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o

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g

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« «» — - > M

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M I -' • • O C

.C X u b

« X — o

c • ^ o ..3 4

C f** • — o a, « o • •

St 3 u ^

Figure Bl. End cap, part Bl.

Bl
UJ

1 1—

CM < \

o

y- ^

"- o m ^

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r^ o m

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Figure B2. Low pass filter plate, part B2.

B2
(N

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f m in ^ S3o u

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B3
CM

00

• LU

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Ld X

^ Q

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B4
eno

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Figure B5. Printed circuit board, part PC2.

B5
BOTTOM VIEW (As seen from inside the mount cap)

PIN 1 P I N 2

P I N 3

P I N 4

WHITE. LO-SIDE CURRENT

GREEN, HI-SIDE CURRENT

RED. HI-SIDE POTENTIAL

BLACK, LO-SIDE POTENTIAL

KEYWAY LOCATION

Figure B6. Wiring convention for the dc bias connector, Jl.

B6
APPENDIX C. Part Drawings Spedfic to Type N Mounts

Figured. Body part A (Type N).

CI
Figure C2. Connector body (Type N), part C2.

C2
-K1

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1^ o

vn 00

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Figure C3. Coupling nut mounting ring (Type N)> part C3.

C3
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Figure C4. Center conductor extension (Type N), part C4.

C4
APPENDIX D. Part Drawings Specific to APC-7 Mounts

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ii

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g

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Dl
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D2
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D3
APPENDIX E.

Drawings for Special Assembly Tools and Microwave Absorber Fabrication

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Figure E2. Mount cap puller, part E2.

E2
Microwave Absorber Fabrication

The following describes the steps necessary for the fabrication of the magnetic microwave absorbers used in the

construction of the mount.

The microwave absorbers are made from a mixture of one part silicon rubber to four parts iron powder and are

cast in a mold made as shown in figure E3. The supplies (with Table A. 2 identification in parentheses), tools,

and parts needed are listed below, followed by the fabrication steps.

1. Silicon rubber (S2)

2. Iron powder (S3)

3. Teflon mold and plugs (see figures E3 and E4)

4. Oven or hot plate

5. Vacuum chamber such as a bell jar and pump

Step 1. Fill the six-mold array with plugs to obtain the configuration shown in figure E4. Use tape on bottom

of mold to keep plugs from falling through.

Step 2. Mix about S g of silicon rubber following the directions on the product data sheet.

Step 3. Add 4 parts by mass of iron and mix thoroughly.

Step 4. Place silicon/iron mixture in the vacuum chamber and pump until all or most outgassing has stopped.

Step S. Pour mixture into mold array, filling each cavity completely.

Step 6. Place the filled mold under vacuum until most of the air bubbles are removed. Add more mixture if

needed and level off top of mold. Remove as much excess as possible.

Step 7. Bake filled mold at 100°C for 1 h.

Step 8. Allow mold to cool, remove cured microwave absorbers by carefully pushing out the largest pegs from

the bottom. Trim off any excess silicon rubber.

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E4
Figure E4. Mold configuration for three sets of microwave absorbers, as viewed from above. Numbers

denote which of the plugs, shown in figure E3, to use.

E5
APFE^a)IX F. Operating Manual

MODEL CN COAXIAL MICROWAVE POWER REFERENCE STANDARD

National Institute of Standards and Technology

Boulder, Colorado 80303

1. GENERAL INFORMATION

The NIST Model CN coaxial microwave power reference standard is a 200 Q thermistor mount especially designed

to be calibrated directly in the NIST coaxial microcalorimeter. The mount is then used as the reference or transfer

standard to calibrate lower echelon transfer instruments. Its physical characteristics are the result of the

microcalorimeter-compatible design. These features are: a small size and mass so it can reach thermal equilibrium more quickly, a body made of copper with no thermal isolation (and no temperature compensation thermistors) for

better thermal transfer to the microcalorimeter, and a better low pass filter on the dc bias leads to minimize rf

leakage. In addition, four leads are brought into the mount very close to the thermistor beads to virtually eliminate

lead resistance errors when used with the N6S Type IV power meter. The copper body with no thermal isolation makes the standard more sensitive to ambient temperature changes, so that more care must be exercised in the use

of the mount than would be needed for a commercial general purpose thermistor mount. In addition, because of

the copper body, the standard must be protected against any mechanical abuse such as blows or being dropped.

2. SPECIFIC INFORMATION

The thermistor bead assembly (thermistor bulkhead) is a modified version of the bulkhead used in the HP Model

8478B thermistor moimt. A copy of the manual for the 8478B is included with this manual. All of the precautions

listed for mechanical shock, biasing, and maximum power input also apply to the Model CN. Note a difference

in the dc connections to the thermistor beads: in the 8478B one side is connected to the mount body (unbalanced),

while in the Model CN both sides float. This allows more flexibility to eliminate instrumentation ground loops.

Before mating the Model CN with any female Type N connector, be sure the critical dimension shown in figure

1 is within the indicated limits. Failure to observe the maximum limit could result in catastrophic damage to the

mount. Also inspect both connectors before use for dirt or damage. Clean or replace the female connector as

needed.

Fl
The mount connector, with its copper outer conductor,

can be easily damaged. However, taking care to

measure and inspect the mating connector, always

using a torque wrench (approximately 1. 13 N • m (10

Ibf • in)), keeping the connector clean, and not

allowing the mount to rotate when connecting or removing it, will give maximum connector life. One

NIST mount has well over 100 connections without

any evidence of wear or damage.

The mount is designed to operate with an NBS Type

IV power meter at a resistance of 200 0. Inadvertent

operation at 100 Q can result in damage to the

thermistors. A four-conductor dc bias cable is

supplied with the mount with either banana plugs or

the appropriate connector for the power meter. Figure

2 shows the pin-out for the mount connector.

, 207 I n 204- 1 n

'

Ty»« N 0lug

Figure 1 . Dimension limits on female Type N

connector.

TOP VIEW

(Aa taan fratn tha cobla I d« of th« connactor)

PIN I PIN 2 PIN 3 PIN

WHITE. LO-SIOE CURRENT

GREEN. HI -SIDE CURRENT

RED. HI -SIDE POTENTIAL

BLACK. LO-SIOE POTENTIAL

KEYWAY LOCATION

Figure 2. Mount bias connector pin-out.

Except for the cap, the mount is made of threaded

parts that are mated. Special wrenches are generally required for the assembly (or disassembly) of the mount.

However, none of the threaded parts are pinned to prevent turning, so it is possible for them to become loose. This

is especially true for the largest part, the mount body, because it cannot be assembled with a wrench. Should any

parts become loose, retighten the assembly by hand and exercise extra care to not torque the mount in such a way

as to loosen the body. If the problem persists, the mount can be returned to NIST to be checked and tightened.

The rear cap on the mount is a sliding fit with the body.

WARNING: Do not pull on or try to remove the cap!

Normally, it is not possible to remove the cap by hand. However, in some mounts the fit is not as tight, so an

inadvertent pull may partially or totally remove the cap. If the cap is partially removed, it can simply be pressed

back into the body. If the cap is completely removed, it must be replaced in the correct orientation. The notch

(keyway) on the miniature dc bias connector is aligned between either one of the shorted internal connector pairs.

S& figure 3. The shorted pairs are determined with an ohm-meter.

The operating frequency range is SO MHz to 18 GHz. The measured effective efficiency data are supplied for this

range. The effective efficiency measurement is valid only at the 10 mW power used in the microcalorimeter. When

using the mount to calibrate a transfer instrument it must be done at 10 mW. This is primarily because the

reference standard is a dual-element coaxial thermistor mount and subject to a power nonlinearity known as the duaiF2
element error. This error is included in the effective

efficiency as measured in the microcalorimeter at 10

mW, but at lower powers, such as 1 mW, it will add

a systematic uncertainty that cannot be calculated or

easily measured.

As p>art of the initial NIST tests on a transfer standard,

the reflection coefficient is measured using a network

analyzer. A copy of an SWR plot from this

measurement is included with the mount. This plot is

otdy intended to show that the mount is within the

manufacturer's specifications. The plot is not intended

as a means to calculate the calibration factor. If the calibration factor is required, you will need to make your own

measurement, adding the appropriate uncertainties.

SHORTED PAIR

(a)

CONNECTOR NOTCH

(b)

Figure 3. (a) End view of the mount with cap

removed, (b) End view of the cap.

The mount serial number is engraved on the cap. WARNING: Do not add marks or attach any labels to the mount/

Marks or labels on the outside of the mount change its thermal characteristics and will prevent it from being

calibrated in the microcalorimeter.

Because the moimt is made of copper and has no thermal isolation, it is very sensitive to external temperature

changes. However, these same factors and its small mass allow it come to thermal equilibrium with the equipment

it is connected to fairly quickly. The following should be done to minimize the temperature induced bias drift and

its effect:

(1) use the mount in a temperature controlled lab,

(2) keep it out of drafts,

(3) use the supplied external insulating sleeve,

(4) handle it with gloves,

(5) wait several minutes after connecting it before making measurements, and

(6) automate the mount voltage measurement so the drift can be corrected (make two rf-off readings, one

before and one after the rf-on reading, and use linear interpolation to calculate an rf-off value as it would

have been at the time of the rf-on reading).

Such measures have been adequate at NIST when using the mount with the six -port transfer instruments.

No schedule for calibration of the standard has been established. Until some history is accumulated, it is

reconunended the mount be recalibrated the first time within one year.

F3

,'n^TrvMrNT ^RfN'TTNC OFFTCC: 1 PP3-77^-025 /89008
NISTTechnical Publications

Periodical

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development in those disciplines of the physical and engineering sciences in which the Institute is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad

range of subjects, with major emphasis on measurement methodology and the basic technology underlying

standardization. Also included from time to time are survey articles on topics closely related to the

Institute's technical and scientific programs. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the Institute's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed

in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NIST, NIST annual reports, and

other special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

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engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

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properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NIST under the authority of the National Standard Data Act (Public Law

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for NIST by the American Chemical Society (ACS) and the American Institute of Physics (AIP).

Subscriptions, reprints, and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC

20056.

Building Science Series—Disseminates technical information developed at the Institute on building materials,

components, systems, and whole structures. The series presents research results, test methods, and

performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NIST under the sponsorship

of other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized

requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NIST administers this program in support of the efforts of private sector standardizing organizations.

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areas of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace.

Order the above N/57 publications from: Superintendent of Documents, Government Printing Office,

Washington, DC 20402.

Order the following NISTpublications—FIPS andNISTIRs—^from the National Technical Information Service,

Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the

official source of information in.the Federal Government regarding standards issued by NIST pursuant to the Federal Property and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1127),

and as implemented by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

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NIST for outside sponsors (both government and non-government). In general, initial distribution is handled

by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161,

in paper copy or microfiche form.
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