Agilent 346A Data Sheet

application

Noise Figure Measurement Accuracy

Application Note 57-2

2

3

Table of contents

Chapter 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Accurate noise figure measurements mean money . . . . . . . . . . . . . . . . . . .5

What will reading this note do for you? . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Chapter 2

What factors affect noise figure measurement accuracy? . . . . . . . . . . . . . . . .7

Sources of error that can be eliminated . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Sources of error that cannot be eliminated . . . . . . . . . . . . . . . . . . . . . . . . .12

Chapter 3

Methods to calculate accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Cascade noise figure accuracy equation . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Measurement simulation method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Chapter 4

A practical look at noise figure accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

The uncertainty versus measurement system noise figure (NF2) curve .15

Noise figure accuracy misconceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Chapter 5

Improving measurement accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

1. Eliminate all removable errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

2. “Increase” device gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

3. Reduce measurement system noise figure (NF2) . . . . . . . . . . . . . . . . . .18

4. Reduce individual uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Appendix

Amplifier and transistor curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Mixer and receiver curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

4

5

Chapter 1
Introduction

Accurate noise figure measurements mean money

Anyone involved in the low-noise microwave business
knows that noise figure is a “money number.” When
measuring and specifying noise figure, the more
accurate a noise figure measurement is, the smaller
the uncertainty guardband needed on the noise figure
specification. The smaller the uncertainty guardband,
the lower the noise figure specification. The lower
the noise figure specification the higher the price
charged.

Low-noise device and system manufacturers want
accurate noise figure measurements for higher
production yields. If a manufacturer of 2 dB noise
figure amplifiers measures to an accuracy of .5 dB,
the amplifiers must measure at most 1.5 dB to be
sure the customer gets 2 dB. If the measurement
accuracy can be tightened to 0.2 dB, amplifiers
measuring 1.8 dB can be shipped.

There are other reasons why accurate noise figure
measurements are important. In addition to improved
yield, manufacturers also want accurate noise figure
measurements so they can price their product higher.
Users of low-noise devices and systems want accurate
measurements to verify they get the performance
they paid for.

Although accurate noise figure measurements are
very important, measurement accuracy is seldom
calculated. Since many things affect a noise figure
measurement, calculating accuracy is complicated
and time consuming.

What will reading this note do for you?

This note is designed to show you these things:

1. Many things can affect the accurate measurement
of noise figure (Chapter 2).

2. You can estimate your measurement accuracy
using statistically-generated curves (Chapter 3).

3. Although it appears complicated, noise figure
accuracy can be practically understood (Chapter 4).

4. You can improve your noise figure measurement
accuracy in a systematic way (Chapter 5).

HP 8970B Noise Figure Meter (10 to 1600 MHz).

HP 8970T Noise Figure Measurement System (10MHz to 18 MHz).

6

7

Chapter 2
What factors affect noise figure measurement accuracy?

Because noise figure is an extremely sensitive (i.e.,
low-level) measurement, many more factors affect
its accurate measurement than other, higher power
measurements.
People measuring noise figure often make the mistake
of considering only one, two, or a few factors when
estimating measurement accuracy. Most often,
considering only a few factors does not adequately
represent true accuracy.

This chapter discusses many error sources in noise
figure measurements. These error sources can be
divided into two groups.

1. Sources of error that can be eliminated

2. Sources of error that cannot be eliminated

Sources of error that can be eliminated include:

a. Dirty or bad connectors (they cause reflections

and make the measurement susceptible to stray
signals)

b. EM susceptance (stray signals are measured as

noise power)

c. Impedance change between “on” and “off”

(especially a problem with transistor
measurements)

d. Using insertion gain instead of available gain (this

causes an error when correcting for second stage
noise contribution)

e. Noise figure and gain discontinuities in the

measurement system (this can cause an error if
the noise figure meter does not tune exactly to
the same frequency between calibration and
measurement)

f. Jitter (the random nature of noise makes one

noise reading different than the next)

g. Double-sideband measurements (a problem with

devices whose noise figure and gain response
varies abruptly with frequency)

Sources of error that cannot be eliminated are
combined and represent the overall accuracy of a
noise figure measurement. They include:

a. Device Noise Figure and Gain (the higher these

are, the more accurate the measurement)

b. Individual Uncertainties–mismatch, ENR, and

instrumentation uncertainty (the lower these are,
the more accurate the measurement)

c. Measurement System Noise Figure (the lower this

is, the more accurate the measurement)

Sources of error that can be eliminated

Before the days of automatic noise figure meters,
eliminating some sources of measurement error was
difficult. If those sources were not minimized, they
were simply ignored and the errors accepted. Today,
with automatic meters like the HP 8970A and 8970B,
many error sources are conveniently eliminated.

There are some sources of error, however, only good
measurement practice can eliminate. Here are those
error sources.

Dirty or Bad connectors: It only takes a small
amount of dirt in a connector to cause insufficient
contact and allow extraneous signals to couple into
the measurement. (And it only takes one dirty
connector to spread dirt to many.)

If there is visible dirt on your connectors, clean them.
A cotton swab and isopropyl alcohol work well.

Connectors do not last forever; they wear. Connectors
with worn plating on the inner or outer conductors
should be replaced. This eliminates the possibility of
loose, intermittent connections.

To learn more about proper connector care, ask your
HP sales representative for Service Note 346B-4
“HP 346B Noise Source RF Connector Care”
(literature Number 00346-90023).

EM Susceptance: Most measurements are made
in environments where stray signals are present.
Since few noise figure measurers have the luxury
of screen rooms, many times these stray signals get
coupled into the measurement. Signals emitted
from computers and other instruments, fluorescent
lights, local broadcast stations, etc., can get coupled
into a measurement through non-threaded connectors
or non-shielded cables.

The HP 8970B Noise Figure Meter eliminates many sources of possible
measurement error—noise contribution from the measurement system,
noise source “off temperature” different than 290K, and compensation
for losses before or after the device under test.

8

Stray signals can cause several tenths of a dB
difference from one measurement sweep to the next
(thus appearing as an unstable measurement).

Stray signals can be easily traced. Shake the
connectors in the measurement signal path and see
if the noise figure changes significantly. If so, you
may have a bad or dirty connector susceptible to
stray signals. Another test is to attach an “antenna”
(wire, etc., ) to a spectrum analyzer and look for
stray signals at the measurement frequency. A third
test, when measuring with an HP 8970A or 8970B, is
to connect to 20 MHz IF output on the HP 8970 rear
panel to a spectrum analyzer. A stray signal will
show up as a spike on the 20 MHz passband.

How are stray signal problems avoided? First, use
threaded connectors in the signal path whenever
possible (non-threaded connectors, like BNC, are
very susceptible to stray signals). Second, use double
shielded cables. Third, enclose the device you are
measuring in a shielding container (this is especially
important if you are measuring noise figure on an
open PC board).

When down-converting measurements, avoid setting
your noise figure meter to intermediate frequencies
(IFs) that could be radiated in your work environment.
Avoid computer clock frequencies. Avoid paging
system frequencies. Avoid common multiple-often
IFs (10, 20, 30 MHz); instead, use IFs like 26 or 27 MHz.

Impedance change between “on” and “off” of
the noise source: When a noise source turns on, the

noise-generating avalanche diode appears as a short
circuit. When off, it appears as an open. Most noise
sources have a matching pad at their output to
minimize the on-to-off impedance difference. In
some measurements, this pad does not provide
sufficient matching and the small impedance
difference can cause errors.

One measurement where this can cause errors is
transistor characterization. In this measurement, the
device-under-test (DUT) is subjected to multiple
input impedances and the corresponding noise
figures and gains are measured. After measuring
at several input impedances, circles of constant
noise figure are plotted and the impedance giving
minimum noise figure is calculated. Since the input
impedance needs to be care-fully controlled, an
on-to-off impedance change from the noise source
is undesirable. Transistor characterization
measurements are generally made using specially­designed noise sources with very small on-to-off
impedance changes (like the HP 346A pictured below).

The HP 346A Noise Source exhibits a much

lower impedance change between on and

off than normal noise sources (for

transistor characterization and

other impedance-sensitive

measurements.)

Stray signals can be seen on a spectrum analyzer.

Figure 2.1 Signals can get coupled into a noise figure
measurement from many different sources (a) flourescent lights
(b) computer and other instruments (c) local tv/radio stations
(d) remote paging systems (e) land-mobile radio.

(b)

(a)

(c)

(e)

(d)

9

Using insertion gain instead of available gain: A
noise figure meter measures noise figure and insertion
gain1. The equation to correct for second stage
contribution requires available gain2, not insertion
gain. An automatic noise figure meter assuming the
insertion gain IS the available gain, uses insertion
gain in the second stage correction equation. This
assumption results in an error.

This error is generally considered to be a mismatch
error and is figured into the overall noise figure
measurement uncertainty. The error can be removed
by measuring the reflection coefficients of the device
output ( o), the source ( s) and the load ( l) and
substituting it into the equation for available gain

Available gain is then substituted into the cascade
gain equation to calculate the noise figure of the
DUT (F1).

F12is the combined DUT/measurement system noise
figure, F2is the measurement system noise figure.
All terms in the above two equations are linear, not
dB, terms. (More about Eq. 2.2 in Chapter 3.)

Noise figure and gain discontinuities in the
measurement system: Occasionally, there is a

component in the measurement system (the down­converting mixer, an amplifier, etc.) that has a noise
figure or gain discontinuity (see Figure 2.2).

Although measurement system noise figure and gain
is measured during the calibration and factored-out
during the measurement, a sharp discontinuity can
cause problems. If the measurement system does not
perfectly tune to the same frequency from calibration
to measurement, it can measure the discontinuity
during calibration and not during measurement. The
noise figure meter then corrects for more second
stage noise than actually present. This results in a
measurement error.

There are a few ways to avoid this problem. First,
see that your measurement system noise figure
and gain response is flat. To do this, measure
system noise figure and gain in very small frequency
increments (1 to 5 MHz). If the response looks fairly
flat, there should be no discontinuity problems.
Second, if a discontinuity is present, use a high gain,
low-noise preamplifier at the measurement system
input. The preamplifier reduces the noise figure
contribution of the measurement system, including
discontinuities. Third, calibrate at the frequencies
you want to measure and approach the measurement
frequency in the same direction as the calibrated
frequency (i.e., from low to high frequency). This
helps avoid non-repeatable tuning due to hysteresis
of any YIG oscillator or YIG filter in the measurement
system.

Jitter: All noise measurements, because of the
random nature of noise, exhibit some degree of
instability, or jitter. The amount of jitter is a function
of the device measured (its noise figure and gain)
and the design of the measuring instrument.

Eq. 2.1

Eq. 2.2

Frequency

(a) Tuning for Calibration (b) Tuning for Measurement

Measurement
System Noise

Figure (or Gain)

Noise Figure Meter
IF Filter

Frequency

Measurement
System Noise

Figure (or Gain)

1. Insertion gain: The gain is measured by inserting the DUT between a generator and load. The numerator of
the ratio is the power delivered to the load while the DUT is inserted. The denominator, or reference power,
is the power delivered to the load while the source is directly connected.

2. Available gain: The ratio of power available from the output of the network to the power available from
the source.

Figure 2.2 If the measurement system has noise figure or gain discontinuities, non-repeatable tuning between (a) calibration and (b)
measurement can cause errors when correcting for second stage contribution.

Figure 2.3 Microwave noise figure measurement set-up
(double-sideband measurement).

Figure 2.4 Double-sideband measurements (1) can cause sideband averaging errors, (2) allow 3rd harmonics to be down-converted
and (3) allow other spurious signals to be coupled into the measurement.

10

Jitter is minimized by averaging many measurements.
(With the HP 8970A or 8970B, jitter can be reduced
to less than .02 dB.) Averaging, or smoothing,
decreases jitter at the expense of decreased
measurement speed.

Since jitter can be reduced to such a small value
(.02 dB), it will not be considered when we calculate
accuracy. If you noise figure meter cannot minimize
jitter to such a small value, you will need to add an
additional jitter error term when determining
uncertainty.

Double-sideband measurements: This section dis­cusses down-converted microwave measurements of
amplifiers and transistors (i.e., non-frequency trans­lating devices).

When a noise bandwidth is down-converted from a
microwave frequency to the tunable range of a noise
figure meter, the desired noise band is not the only
noise down-converted. There are two main noise
bands down-converted plus possible harmonic noise
bands. If a measurement system allows both main
noise bands to be down-converted, it is a double­sideband (DSB) measurement system. If the mea­surement system prevents one sideband (commonly
known as the image band ) and allows the other
noise sideband (the desired band) to be down­converted, it is a single-sideband (SSB) measurement
system. Because DSB measurements allow more
than one band of noise to be down-converted, errors
may be introduced in the measurement.

One source of error in DSB measurements involves
the two main down-converted noise bands (fLO+ f

IF

and fLO- fIF). The noise figure meter, tuned to the IF,
measures the combined noise from the two down­converted frequencies. The noise figure meter does
not “know” the noise it measures is from two bands.
Because of this, the noise figure value displayed is
an average of the two down-converted bands. If the
device response between the two sidebands is not
linear, the average value can differ from the actual
value. (see (1) in Figure 2.4). (If the device mea­sured has a flat frequency response, like a broadband
amplifier, there will probably not be much sideband­averaging error.)

RF IF

LO

Output

Input

Noise

Source

Calibratioin

DUT

Local

Oscillator

HP-IB

Noise Source

Drive

Noise Figure Meter

> (1)

Device

Input

(3) Spurious Signal

Leaks Through Mixer

Noise Output
From Device

Downconverted Noise

(2)

Frequency

fLO – f

IF

fLO + f

IF

f

LO

3fLO – f

IF

3fLO + f

IF

3f

LO

11

The fLO± fIFnoise sidebands, although dominant, are
not the only down-converted noise bands a DSB sys­tem measures. A down-converting mixer generates
harmonics of the local oscillator (2fLO, 3fLO, etc.) In
double balanced mixers, the even harmonics (2fLO,
4fLO, etc. )are usually well suppressed; the odd
harmonics (3fLO, 5fLO, etc.) are not. As a result, odd
harmonics mix with and down-convert RF noise just
like the fundamental LO frequency (see (2) in Figure

2.4). The 3rd harmonic is the dominant odd harmon-

ic—its mixing products can be as large as only 10 dB
down from the fundamental responses. As in the
case of image noise, these signals are averaged into
the final result and, if large enough, cause errors.

Other spurious signals can also be coupled into a
DSB measurement through the IF and cause
measurement errors (see (3) in Figure 2.4).

Three aspects of a DSB measurement can cause
problems when characterizing transistors. First,
since two different input frequencies are being
measured in a DSB measurement, characterization is
taking place at two different input impedances.
Second, the physical distance between the device
and tuner causes a phase shift as the two noise side­bands travel from the device, reflect from the tuner
and return to the device input (since in a transistor
characterization measurement, you want to
characterize impedance in terms of phase as well as
magnitude, a phase measurement error will result).
Third, an adjustable tuner creates a sharp noise
figure (or gain) variation. Due to its averaging
nature, a DSB measurement will tend to smooth out
the dip (or peak), giving an inaccurate reading.

Single-sideband measurements eliminate double­sideband problems by pre-selecting the desired noise
sideband before it is down-converted. This way, all
undesirable signals are removed before they are
down-converted.

Single-sideband measurements are made either with
a fixed filter (for narrowband systems), a tunable
YIG filter (like the one in the HP 8971B pictured
below for broadband systems), or an image-reject
mixer. Filtering allows only the desired measurement
band frequency to be downconverted (see Figure

2.5); an image reject mixer does not eliminate 3rd
order harmonic mixing or spurious responses.

> (1)

Device

Input

(3)

Noise Output
From Device

Downconverted Noise

(2)

Frequency

fLO – f

IF

fLO + f

IF

f

LO

3fLO – f

IF

3fLO + 3f

IF

3f

LO

SSB
Filter

Figure 2.5 A single-sideband filter gets rid of double-sideband problems: (1) sideband averaging errors, (2) 3rd order harmonics and
(3) other spurious signals.

The HP 8971B Noise Figure Test Set (middle instrument) uses a
temperature-compensated YIG-tuned filter to make single­sideband measurements. In the HP 8970T system configuration
pictured here, the HP 8970B Noise Figure Meter (top) acts as
the controller for both the HP 8971B and HP 8671B Synthesized
CW Generator (bottom).

12

Suppliers and users of low noise devices all want a
standard way to measure noise figure so their
answers are accurate and agree. The accuracy of a
DSB measurement depends on the flatness of the
DUT noise figure and gain response; the accuracy of
a SSB measurement is independent of DUT flatness.
This makes SSB the only standard way to make
down-converted noise figure measurements.

Sources of error that cannot
be eliminated

There are a few noise figure measurement error
sources that cannot be eliminated. (They can be
reduced, but not eliminated.) Listed below are these
errors. In Chapter 3, a noise figure measurement
accuracy is calculated from these errors.

These non-removable factors can be divided into
three groups:

1. Device under test (DUT) noise figure and gain

2. Individual uncertainties:

Noise figure and Gain Instrumentation
uncertainty: Noise figure instrumentation

uncertainty is typically the linearity of the noise
figure meter’s detector. Gain instrumentation
uncertainty is typically the detector and attenuator
linearity of the meter. They are given as noise
figure meter specifications.
ENR uncertainty: The uncertainty between the
calibrated and actual (National Bureau of
Standards) value. This is and uncertainty only
given for calibrated points; it does not take
into account ENR variation with frequency
between the calibrated points.
Mismatch uncertainty: There are typically three:
(1) mismatch between the noise source and
DUT input (2) mismatch between the DUT
output and the measurement system input and
(3) mismatch between the noise source output
and the measurement system input (during
calibration).

3. Measurement system noise figure: The
measurement system noise figure includes not
only the noise figure meter itself, but also any
external devices used for down conversion and
filtering. It typically ranges from 4 to 28 dB.

13

Calculating noise figure accuracy is not a simple,
straight-forward calculation. There are several
reasons for this. One, as stated previously, many
sources of error affect noise figure measurement
accuracy (ENR uncertainty, instrumentation uncer­tainty, mismatch uncertainty, etc.) Two, the noise
power measurement results are not readily available
from a noise figure meter to let someone calculate
noise figure accuracy based on the power measure­ments. Three, the results that are available (DUT
noise figure and gain, measurement system noise
figure) are dependent on one another, the sensitivity
of how one variable affects another needs to be
taken into account.

This chapter discusses two methods of calculating
measurement accuracy.

The first method is the cascade noise figure
equation method. This method provides good intu­itive understanding of noise figure accuracy but
makes simplifying assumptions that are not always
valid; we will use it as an instructional tool.

The second method is the statistically-based
measurement simulation method. This method
provides a better representation of noise figure
measurement accuracy than the cascade method.
Several statistically-generated uncertainty curves
are provided in the appendix to help you estimate
the accuracy of your measurement. (These curves
are Uncertainty versus DUT Noise Figure and Gain
curves; the curves we will describe in this chapter
are Uncertainty versus Measurement System Noise
Figure curves. Uncertainty versus Measurement
System Noise Figure curves are useful in explaining
noise figure measurement accuracy theory. Un­certainty versus DUT Noise Figure and Gain curves
are more useful in calculating a real-life measure­ment accuracy because while DUT noise figure and
gain vary a lot in a typical measurement situation,
measurement system noise figure does not.)

Cascade Noise figure accuracy equation

A noise figure meter measures the combined noise
figure of the DUT and the measurement system.
(See Figure 3.1).

Figure 3.1 Typical noise figure measurement setup. Device and
measurement system noise figures combine according to the
cascade gain equation.

To determine the noise figure of the DUT alone, an
automatic noise figure meter (like the HP 8970B)
subtracts the noise contribution of the measurement
system (i.e., the HP 8970B itself) from the cascaded
DUT/measurement system noise figure3:

F2, the measurement system noise figure, is measured
during calibration. F12is the DUT-plus-measurement­system measurement. G1is the device available gain.
G1is calculated by taking a noise power ratio
between the measurement (F12) and calibration (F2).
(These are linear, not dB, terms.)

The measurement of DUT noise figure (F1) can be
thought of as a calculation based on three separate
measurements—F12measurement, F2measure-ment,
and G1measurement. (G1is actually not a measure­ment but a derivation from the F2and F12measure­ments.) If we know how F1varies with changes in
the F12, F2, and G1measurements, we can calculate
an overall accuracy for F1based on how errors in
each of those measurements affect F1.

By taking the partial derivatives of F12, F2and G

1

with respect to F1in the Eq. 3.1, we can calculate
how sensitive F1is to the three measurements. This
partial-derivative equation, in dB terms, is:

Overall uncertainty, ∆NF

1

, is then calculated by
squaring each item, adding them, then taking the
square root (i.e., root-sum-of-squares or RSS).

3. This equation is based on the cascade noise figure
equation. See page 17 of HP Application Note 57-1
for more about second stage noise contribution.

Noise

Source

DUT

Measurement System

(HP 8970B, downconverter,

Filters, Switches, etc.)

F1, G1 F2

F12 = F1 +

F2 – 1

G1

Chapter 3
Methods to calculate accuracy

Eq. 3.1

Eq. 3.2

14

The cascade noise figure accuracy equation gives a
good picture of how the error-causing factors affect
overall accuracy (e.g., as G1increases, each term
in the equation decrease. When the terms are then
added in a root-sum-of-squares manner, you can see
that overall uncertainty decreases). Eq. 3.2 is not,
however, recommended when calculating accuracy—
it makes the assumption that gain is a separate
measurement (remember, G12is only a derivation).
This assumption makes the resulting uncertainty
unrealistically large.

Measurement simulation method

The measurement simulation method uses a computer
to simulate probable measurement conditions. It uses
those conditions to simulate probable measurement
results and then calculates a realistic uncertainty based
on many such simulated measurements.

The simulation method practically assumes that
each source of measurement error (instrumentation
uncertainty, ENR uncertainty, etc.,) is distributed in a
Gaussian (bell-shaped) probability distribution. The one
exception is reflection coefficient phase; this is assumed

to be uniformly distributed between 0 and 2π.

The standard deviations for the simulated
measurement conditions are derived from instrument
specifications. The instrument specifications are
assumed to be at 3 standard deviations (this is very
conservative for HP instrumentation).

The computer first generates a random variate
corresponding to each measurement condition.
It then determines the actual noise figure measure­ment result based on those conditions. After many
“measurements” (300 to 400), the computer then
calculates boundaries in which a certain percentage
of the “measurements” lie (95% boundaries were
used for the curves in the appendix). These
boundaries define the measurement uncertainty.

The appendix shows several uncertainty curves
generated with the measurement simulation method.
If your measurement conditions are close to those
of the curves, use these curves to calculate your
measurement uncertainty. (Keep in mind these are
uncertainty versus DUT noise figure plus gain curves,
not uncertainty versus measurement system
noise figure.)

The measurement simulation method gives a realistic
representation of measurement accuracy. It, like the
cascade noise figure method, has some drawbacks.
One, it can be complicated to program and two, it can
be computationally time-consuming. The curves in the
appendix, however, should be sufficient in showing
you the accuracy of many of your measurements.

Enter

System

specifications

(a) (b) (c)

(d)

Generate

Measurement

Conditions

Calculate

Measurement

Result

Calculate

Uncertainty

300–400

Measurements

Measurement System Noise Figure (dB)

0 5 10 15 20 25 30

3.0

2.5

2.0

1.0
.09

.08
.07

.06
.05

.04

.03

.02

.01

Measurement Uncertainty (dB)

(a)

(b)

Figure 3.2 Flow graph of measurement simulation method of
calculating noise figure accuracy. (a) Programmer enters mea­surement system specifications into the computer. (b) Computer
generates typical measurement conditions based on system
specifications and a Gaussian probability distribution.
(c) Computer calculates the measurement result. After 300 to 400
of these measurements, (d) the computer calculates uncertainty
boundaries where 95% of the simulated measurements fall
within those boundaries.

Figure 3.3 Comparison of (a) cascade noise figure accuracy
equation and (b) measurement simulation method for a typical
DUT and measurement system.

15

This chapter discusses a number of noise figure
accuracy issues on a practical level. This should
give you a better understanding of noise figure
measurement accuracy so you are more comfortable
making and specifying the measurement.

Specifically, this chapter (1) shows a practical
way to think about noise figure accuracy and
(2) discusses and dispels some noise figure
accuracy misconceptions.

The uncertainty versus measurement system
noise figure (NF2) curve

A good way to get an intuitive understanding of
noise figure accuracy is to study a graph. One such
graph is total measurement uncertainty versus
measurement system noise figure (Figure 4.1).

Figure 4.1 The Uncertainty (DNF1) versus Measurement System
Noise Figure (NF2) curve

Each of the three error sources mentioned in
Chapter 2 (device noise figure and gain, individual
uncertainties, and NF2) affect the uncertainty curve
differently.

Device noise figure and gain: Changing these
factors shifts the curve left or right. Higher device
gain and/or noise figure shifts the uncertainty curve
to the right (see Figure 4.2) This means higher
device gain (and/or noise figure) gives better
measurement accuracy for a given NF2. In short, a
device with high gain or high noise figure can be
measured with greater accuracy than one with lower
gain or noise figure.

As a general rule, the more device or input noise power
measured, with respect to measurement system noise
power, the more accurate the measurement will be.
Therefore, if a device has high gain, a lot of amplified
input noise will be measured; as a result, measurement
accuracy will be good. If a device has a high noise
figure, a lot of DUT noise will be measured; again,
accuracy will be good.

Figure 4.2 High gain or noise figure devices shift the curve to
the right (lower uncertainty results).

Individual uncertainties: Changing the ENR,
instrumentation, and mismatch uncertainties lowers
or raises the uncertainty curve. (See Figure 4.3.)
(Changing these uncertainties also tends to decrease
or increase the curve’s slope.) Measurement accuracy
can be improved by lowering one or more of the
individual uncertainties.

NF2 (dB)

∆NFI (dB)

NF2 (dB)

∆NFI (dB)

Higher
Device
Gain
Noise
Figure

Lower

Uncertainty

Chapter 4
A practical look at noise figure accuracy

16

Figure 4.3 Lower ENR, mismatch, and instrumentation
uncertainties shift the curve downward (lower overall
uncertainty results).

Measurement system noise figure (i.e., NF2):

Changing the noise figure of the measurement
system moves the measurement uncertainty along

the curve. Figure 4.4 shows that lowering measure-
ment system noise figure can have a large effect on
measurement accuracy, much more so than lowering
the individual uncertainties. (Chapter 5 explains how
to reduce measurement system noise figure.) When
measuring low gain/low noise figure devices (like
transistors), a low system noise figure is necessary
to make an accurate measurement.

Noise figure accuracy misconceptions

The uncertainty versus NF2 curve does more than
just give an intuitive feel of how the sources of error
affect overall accuracy. It also helps to visualize
accuracy in a way to clearly dispel some common
misconceptions about noise figure accuracy. Here
are two such misconceptions.

“Instrumentation uncertainty is VERY significant”

Many people measuring noise figure mistakenly
consider the noise figure meter’s instrumentation
uncertainty as the main indicator of measurement
accuracy. The truth is that instrumentation
uncertainty contributes very little to the overall
measurement uncertainty.

NF2 (dB)

∆NFI (dB)

Lower
Overall
Uncertainty

Lower Measurement
Uncertainties

Figure 4.4 Lower measurement system noise figure (NF2) moves
the uncertainty along the curve (lower uncertainty results).

NF2 (dB)

∆NFI (dB)

Lower
Uncertainty

Lower
System
Noise
Figure

NF2 (dB)

0 5 10 15 20 25 30

3.0

2.5

2.0

1.0
.09

.08
.07

.06
.05

.04

.03

.02

.01

∆NFI (dB)

∆F = 0.1 dB

∆G = 0.15 dB

F = 0
G = 0

Figure 4.5 Comparison of effect of normal and zero
instrumentation uncertainty on overall uncertainty.

17

The uncertainty versus NF2 curve shows how little
the instrumentation uncertainty contributes to mea­surement inaccuracy. Figure 4.5 compares overall
measurement accuracy using the HP 8970A or 8970B
instrumentation accuracy (0.1 dB) to the overall
measurement accuracy if the instrumentation
uncertainty were zero. For this particular DUT noise
figure and gain and a NF2 of 6 dB, the difference in
overall uncertainty is only about 0.03 dB (and that is
comparing the HP 8970 to a perfect meter!) You can
see that very little is gained in accuracy when
instrumentation uncertainty is eliminated, much
less just reduced.

“Measurement system noise figure is NOT
significant”

Most people do not even consider measurement
system noise figure as having an effect on their
measurement accuracy. Earlier we learned that
low noise/low gain devices shifted the uncertainty
curve to the left. This means that even for moderate
measurement system noise figures (8 to 10 dB), the
total uncertainty lies on the upward slope of the
curve. Reducing NF2 by several dB can improve
measurement uncertainty by several tenths of a dB
to a dB or two.

In every measurement, it is advantageous to minimize
NF2’s effect on measurement accuracy. Reducing JNF2
is discussed in the next chapter.

18

Knowing a systematic way to improve measurement
accuracy is just as important as knowing how to
improve the sources of error. This chapter discusses
a logical order for improving measurement accuracy:

1. Eliminate all removable errors

2. “Increase” device gain

3. Reduce NF2

4. Reduce individual uncertainties

1. Eliminate all removable errors

These factors were mentioned in Chapter 2. Refer to
Chapter 2 to find out how to eliminate them.

2. “Increase” device gain

Device noise figure and gain usually cannot be
changed to get a more accurate measurement. The
DUT can be “chosen,” however, for best possible
measurement accuracy. In a receiver front end, the
downconverting mixer is followed by an IF amplifier.
Typically the combination mixer?IF amplifier noise
figure is the important noise figure specification of
the receiver. Because of the added IF amplifier gain,
a better measurement uncertainty results if the mix­er/IF amplifier combination is measured, rather than
the mixer alone.

As a general rule, for a more accurate measurement,
“choose” the device under test for as much gain as
possible.

3. Reduce measurement system noise figure

(NF2)

In many cases, reducing NF2 improves accuracy
more than any of the other steps.

Figure 5.1 Uncertainty versus NF2 graph showing systematic
approach to measurement accuracy improvement: (1) reduce
(minimize) NF2 then (2) reduce individual uncertainties.

As NF2 gets smaller, the uncertainty versus NF2
curve flattens out to a base. If NF2 is reduced so the
uncertainty lies on the curve base, NF2’s effect on
accuracy has been virtually negated.

Here is a simple approximation that helps determine
the largest value NF2 can be and still be on the curve
base:

(This approximation is determined by observation
of the uncertainty curves in the appendix.) NF2
can be reduced to this minimized level with a low
noise preamplifier in the measurement system. If
your current NF2 meets the above condition, your
uncertainty lies on the curve base and a preamplifier
is not needed. It is important to note, however, that
even if the measurement system has a noise figure
that seems low (6 dB, for example), the minimized
NF2 value depends on the noise figure and gain of
the DUT.

1. In other HP documentation, this equation uses
a 15 dB instead of a 5 dB difference. The 15 dB
difference is derived, by observation, from the
cascade noise figure accuracy equation; the 5 dB
difference is derived, by observation, from the
measurement simulation curves in the appendix.

Chapter 5
Improving measurement accuracy

NF2 (dB)

∆NFI (dB)

(1)

(2)

Eq. 5.1

19

Figure 5.2 Measurement system set-up with preamp.

Next, once the minimized NF2 is calculated, calculate
the noise figure and gain of the preamplifier needed.

A preamplifier will lower F2 (NF2) according to the
cascade gain equation:

where Fpaand Gpaare the preamplifier’s noise
figure and gain, F2

current

is the current measurement

system noise figure and F2

reduced

is the new
(reduced) measurement system noise figure. (All
terms in this equation are linear, not logarithmic.)

The first step in choosing a preamplifier is choosing
its noise figure. Eq. 5.2 shows that F2

reduced

can
never be lower than the preamplifier noise figure
(Fpa). Therefore, if NF2 needs to be reduced to 3 dB
(F2

reduced

= 2), a less-than 3 dB noise figure

preamplifier is needed.

Once the preamplifier noise figure is determined, its
gain is calculated according to the cascade gain
equation mentioned above:

The noise figure and gain of the preamplifier can also
be determined graphically (see Figure 5.3). To use
the graph:

1. Choose the preamplifier’s noise figure on the left

side of the graph (i.e., choose a NFpacurve lower
than NF2

reduced

).

2. Follow the NFpacurve to the right until it

intersects with the grid line representing the
NF2

reduced

value.

3. Follow the vertical grid line at the intersection up

(or down) until it intersects with the NF2

current

on the diagonal lines.

4. Follow the intersecting horizontal grid line to the

right to get the preamplifier gain needed.

Figure 5.3 Graph to calculate preamp noise figure and gain.
(Procedure for use is given in text.) Example shown: To reduce
NF2

current

(25 dB) to NF2

reduced

(4 dB), a 2 dB noise figure,

25 dB gain preamplifier is needed.

If you already have a preamplifier, you can use the
graph in the opposite direction to calculate how
much it will reduce the NF2.

A few more words about reducing measurement
system noise figure. First, always try to reduce
measurement system noise figure, even if your
preamplifier does not reduce it to the curve’s base
(every little bit helps). Second, if you have two
devices with gain, use one as a measurement
system preamplifier and measure the other. Third,
the preamplifier input impedance becomes the
measurement system’s input impedance. A
preamplifier’s input match is typically not very
good. Improving mismatch is part of the next topic.

There is an upper limit to the preamplifier gain in a
measurement system. Too much power at the noise
figure meter input could overload it, causing inaccu­rate measurements or damage. The input power to
the noise figure meter is:

Input

Noise

Source

Calibratioin

DUT

Noise Source

Drive

Noise Figure Meter

Low Noise

Preamplifier

Measurement

20

18

16

14

12

10

8

6

4

2

0

18

16

14

12

10

8

6

4

2

0NF

pa

= dB

NF

reduced

(dB)

40

36

32

28

24

20

16

12

8

4

0

35 dB

30 dB

25 dB

20 dB

15 dB

10 dB

NF2

current

= 5 dB

Pin = -174 dBm/Hz + ENR(dB) + 10 log

(BWpreamp HZ) + NF1(dB)
+ G1(dB) + Gpreamp (dB)

Eq. 5.2

Eq. 5.3

Eq. 5.4

20

In the case of the HP 8970T, Pin should not exceed
the -20 dBm maximum operating limit. As an example,
a 6-18 GHz, 20 dB gain system preamplifier is used in
a HP 8970T measurement system to measure a 5 dB
noise figure, 20 dB gain, 6-18 GHz amplifier. The
noise source has 15.2 dB ENR.

This power is higher than the HP 8970T input rating.
Use a 10 dB pad at the preamplifier output to reduce
the HP 8970T’s input power below its maximum
operating limit.

Another preamplifier specification needing consider­ation is the gain compression point. The preamplifi­er’s gain compression should be 9 dBm or greater.
This helps keep the measurement system linear, pre­venting further measurement errors.

Preamplifiers meeting the specifications outlined in
this section can be purchased from several manufac­turers. Two such manufacturers are: Avantek, in
Santa Clara, CA (408-727-0700) and Miteq, in
Hauppauge, NY (516-543-8873).

4. Reduce individual uncertainties

Once NF2 is reduced to the uncertainty curve base,
measurement accuracy is further improved by
reducing the individual uncertainties. (See Figure 5.1.)

Reduce Mismatch (add an isolator to

measurement system input): An isolator at the

measurement system front end reduces mismatch
and, in turn, measurement uncertainty. An isolator
between the noise source and DUT also helps to
reduce measurement uncertainty but may introduce
other problems (like out of band resonances and
reflections from lower quality connectors).

Since an automatic noise figure meter cannot
calibrate out loss before the DUT, the isolator loss
needs to be compensated during the measurement.

Pads (attenuators) also reduce mismatch. Pads,
however, have high noise figures. The accuracy
improvement gained in improved match is often
lost in NF2 degradation. An isolator provides a
match as good or better than a pad with lower
noise contribution.

Reduce ENR uncertainty (have the noise
source calibrated as accurately and as often as
possible): The HP 346 noise source you buy is 2 or 3

calibration generations removed (depending on
frequency) from the National Bureau of Standards.
Each level of calibration adds a small amount of
uncertainty.

Noise source ENR uncertainty can be improved
by eliminating one or more calibration generations.
HP Standards Lab offers noise source re-calibration
services. This typically eliminates one calibration
generation. (Contact the nearest HP service center
for more details.)

The National Bureau of Standards also has noise
source calibration services. For more details, contact
the NBS directly.

Summary

This note has shown you that:

1. Many things can affect the accurate measurement
of noise figure (Chapter 2).

2. You can estimate your measurement accuracy
using statistically-generated curves (Chapter 3).

3. Although it appears complicated, noise figure can
be practically understood (Chapter 4).

4. You can improve the accuracy of your noise figure
measurement in a systematic way (Chapter 5).

This application note was designed to give you
the information needed to maximize your noise
figure measurement time and money. Above all,
Hewlett-Packard wants you to make the most
accurate, and profitable, noise figure measurements
possible.

Pin = –174 dBm/Hz + 15.2 dB + 10 log

(18 x 109 – 6 x 10

9Hz

)

+ 5 dB + 20 dB + 20 dB

Pin = –13 dBm

21

The following are Uncertainty versus DUT Noise
Figure and Gain graphs. (DUT noise figure and gain
is simply the dB sum of the device-under-test noise
figure and gain.) All curves assume an HP 346 Noise
Source is used (SWRout = 1.25; ENR uncertainty =
.1 dB). They also assume that an HP 8970A or 8970B
Noise Figure Meter, or HP 8970T Noise Figure
Measurement System (or HP 8970B Noise Figure
Meter, 8971A Noise Figure Test Set, and recommended
LO) is used. Figures Ax.x are for amplifiers and
transistors; figures Bx.x are for mixers and receivers.

Note: The following graphs seem to show that
the HP 8970B measures more accurately than the
HP 8970T system. Keep in mind that the HP 8970T
system eliminates many errors due to double sideband
measurements. These errors are NOT accounted for
in the HP 8970B accuracy calculation; it is assumed
that the user completely eliminates these errors in
the user’s measurement system.

Appendix

Figure A 1.1

Device under test: Amplifier or transistor

SWR input = 1.0
SWR output = 1.0

Measurement system: HP 8970A or 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 1.2

Device under test: Amplifier or transistor

SWR input = 1.5
SWR output = 1.5

Measurement system: HP 8970A or 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Amplifier and Transistor Curves

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

NF2 = 5 dB 10 dB 15 dB 20 dB 25 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB

15 dB 20 dB 25 dB

NF2 = 5 dB

22

Figure A 1.3

Device under test: Amplifier or transistor

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970A or 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 1.4

Device under test: Amplifier or transistor

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970A or 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 2.1

Device under test: Amplifier or transistor

SWR input = 1.0

SWR output = 1.0
Measurement system: HP 8970A or 8970B (with iso­lator)

SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dBNF2 = 5 dB 15 dB 20 dB 25 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

NF2 = 5 dB 10 dB 15 dB 20 dB 25 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

NF2 = 5 dB 10 dB 15 dB 20 dB 25 dB

23

Figure A 2.2

Device under test: Amplifier or transistor

SWR input = 1.5

SWR output = 1.5
Measurement system: HP 8970A or 8970B

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 2.3

Device under test: Amplifier or transistor

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970A or 8970B

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 2.4

Device under test: Amplifier or transistor

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970A or 8970B

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB

15 dB 20 dB 25 dB

NF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dBNF2 = 5 dB 15 dB 20 dB 25 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

NF2 = 5 dB 10 dB 15 dB 20 dB 25 dB

24

Figure A 3.1

Device under test: Amplifier or transistor

SWR input = 1.0
SWR output = 1.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB
Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 3.2

Device under test: Amplifier or transistor

SWR input = 1.5
SWR output = 1.5

Measurement system: HP 8920T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB
Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 3.3

Device under test: Amplifier or transistor

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB
Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

NF2 = 5 dB 10 dB 15 dB 20 dB 25 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

25

Figure A 3.4

Device under test: Amplifier or transistor

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB
Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 4.1

Device under test: Amplifier or transistor

SWR input = 1.0
SWR output = 1.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 4.2

Device under test: Amplifier or transistor

SWR input = 1.5
SWR output = 1.5

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

26

Figure A 4.3

Device under test: Amplifier or transistor

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure A 4.4

Device under test: Amplifier or transistor

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 1.1

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 1.0

Measurement system: HP 8970A or HP 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

Mixer and Receiver Curves

27

Figure B 1.2

Device under test: Mixer or receiver

SWR input = 1.5
SWR output = 1.5

Measurement system: HP 8970A or HP 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 1.3

Device under test: Mixer or receiver

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970A or HP 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 1.4

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970A or HP 8970B

SWR in = 1.7
Noise figure instrumentation

uncertainty = .1 dB

Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

28

Figure B 2.1

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 1.0

Measurement system: HP 8970A or HP 8970B;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB
Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 2.2

Device under test: Mixer or receiver

SWR input = 1.5
SWR output = 1.5

Measurement system: HP 8970A or HP 8970B;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB
Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 2.3

Device under test: Mixer or receiver

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970A or HP 8970B;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB
Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 15 dB 20 dB 25 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dBNF2 = 5 dB 15 dB

29

Figure B 2.4

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970A or HP 8970B;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .1 dB
Gain instrumentation

uncertainty = .15 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 3.1

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 1.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 3.2

Device under test: Mixer or receiver

SWR input = 1.5
SWR output = 1.5

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dBNF2 = 5 dB 15 dB

Figure B 3.3

Device under test: Mixer or receiver

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 3.4

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO
SWR in = 2.0
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 4.1

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 1.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

30

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

31

Figure B 4.2

Device under test: Mixer or receiver

SWR input = 1.5
SWR output = 1.5

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 4.3

Device under test: Mixer or receiver

SWR input = 2.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

Figure B 4.4

Device under test: Mixer or receiver

SWR input = 1.0
SWR output = 2.0

Measurement system: HP 8970T or HP 8970B, 8971B,

recommended LO;

(with isolator)
SWR in = 1.2 (isolator SWR)
Noise figure instrumentation

uncertainty = .25 dB

Gain instrumentation

uncertainty = .45 dB

Noise source: HP 346

SWR out = 1.25
ENR uncertainty = .1 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

DUT Noise Figure + Gain (dB)

0 5 10 15 20 25 30

3
2

1

.5
.4
.3

.2

.1

Measurement Uncertainty ∆NFI (dB)

10 dB 20 dB 25 dB15 dBNF2 = 5 dB

For more information about
Hewlett-Packard test and measurement
products, applications and services,
and for a current sales office listing,
visit our web site, http://www.tmo.hp.com.
You can also contact one of the following
centers and ask for a test and
measurement sales representative.

United States:

Hewlett-Packard Company
Test and Measurement Call Center
P.O. Box 4026
Englewood, CO 80155-4026
1 800 452 4844

Canada:

Hewlett-Packard Canada Ltd.
5150 Spectrum Way
Mississauga, Ontario
L4W 5G1
[phone]

Europe:

Hewlett-Packard
European Marketing Centre
P.O. Box 999
1180 AZ Amstelveen
The Netherlands
(31 20) 547 9900

Japan:

Hewlett-Packard Japan Ltd.
Measurement Assistance Center
9-1, Takakura-Cho, Hachioji-Shi,
Tokyo 192, Japan
Tel: [phone]
Fax: [phone]

Latin America:

Hewlett-Packard
Latin American Region Headquarters
5200 Blue Lagoon Drive, 9th Floor
Miami, Florida 33126, U.S.A.
[phone]/4220

Australia/New Zealand:

Hewlett-Packard Australia Ltd.
31-41 Joseph Street
Blackburn, Victoria 3130, Australia
1 800 629 485

Asia Pacific:

Hewlett-Packard Asia Pacific Ltd.
17-21/F Shell Tower, Times Square,
1 Matheson Street, Causeway Bay,
Hong Kong
Tel: [phone]
Fax: [phone]

Data Subject to Change
Copyright© 1998
Hewlett-Packard Company
Printed in U.S.A. 11/88
5952-3706