HP 8901A User Manual

HP 8901A Modulation Analyzer

H

150 kHz to 1300 MHz

Product Overview

Measurements*

Frequency

Range: 150 kHz to 1300 MHz
Resolution:

10 Hz below 1000 MHz,
100 Hz above 1000 MHz

Input Level:

Automatic Mode: −20 dBm to
+30 dBm
Manual Mode: Typically

−

60 dBm to +30 dBm

Power

Display: Peak envelope power
Range: 1 milliwatt to 1 watt
Accuracy: Typically ±1.5 dB

Input Power Protection:

>25 watts

Outstanding signal
characterization

Applications

Mobile Radio

The HP 8901A Modulation Analyzer combines all the capabilities
necessary for making accurate transmitter measurements. It
can be used in making all the tests listed below. It can also be
used to test modules and subassemblies from either the trans­mitter or receiver. For reliability, input power protection reduces
the chance of accidentally damaging the modulation analyzer by
connecting it directly to a high power transmitter.

• Carrier power

• Carrier frequency and stability

• AM depth

• FM deviation

• Hum and noise

• Incidental AM or FM

• Modulation limiting

- Instantaneous

- Steady state

• Audio frequency response

Modulation

Frequency Modulation

Rates: 20 Hz to 200 kHz
Deviations: to 400 kHz
Accuracy: ±1% of reading ±1 digit

for rates 30 Hz to 100 kHz

Amplitude Modulation

Rates: 20 Hz to 100 kHz
Depths: to 99%
Accuracy: ±1% of reading ±1 digit

for rates 50 Hz to 50 kHz and
depths >5%

Phase Modulation

Rates: 200 Hz to 20 kHz
Deviations: to 400 radians
Accuracy: ±3% of reading ±1 digit

Maintenance and Metrology

Accurately measuring modulation has long been a problem for
metrology laboratories. The HP 8901A Modulation Analyzer
helps solve this problem two ways. First, it provides an extremely
accurate method of measuring AM depth and FM deviation, and
it recovers the modulation with little degradation for making
measurements such as modulation distortion. Second, the optional
calibrators provide a precise modulation source for calibration.
There are many metrology and maintenance uses for the modula­tion analyzer. They include:

• Signal generator calibration

• Modulation calibration standard

• VCO and VCXO characterization

*All parameters describe performance in automatic operation or properly set manual conditions. Specifications
describe the instrument’s warranted performance. Supplemental characteristics (shown in italics) are intended to
provide information useful in applying the instrument by giving typical, but non-warranted, performance parameters.

FeaturesApplications, cont.

Research and
Development

The accuracy and versatility
of the modulation analyzer
make it a very useful labora­tory instrument for charac­terizing a wide variety of
devices and assemblies.
When used with a modulated
signal source the modulation
analyzer can make stimulus­response measurements for
direct measurement of a
device’s effects on such
signals. Because of its wide
frequency range, it can
measure the performance
of both RF and IF assemblies.
Characterizing modulated
sources for sensitivity,
distortion, and incidentals,
and measuring the noise
performance of local
oscillators is also possible.

• Mixer and Amplifier com­pression

• Local oscillator residual FM

• Modulator characterization

• Incidental AM or FM

• RF and IF characterization

Complete Signal
Characterization

The HP 8901A Modulation Analyzer
brings together in one instrument
several RF signal measurement
capabilities. It is more than just a
high quality modulation meter. It
accurately measures carrier fre­quency and peak input power in
addition to completely characteriz­ing modulation. This unique combi­nation of capabilities makes the
HP 8901A Modulation Analyzer an
extremely powerful tool for analyz­ing signals. In normal use it elimi­nates the need to frequently connect
and disconnect several instruments,
such as counters and power meters.
The modulation analyzer is fully
programmable and can be used as
part of an automatic system to make
all these measurements under
remote control.

Single Key Measurements

The HP 8901A Modulation Analyzer
features easy to use controls. In
automatic operation, all major func­tions are selected by pushing a
single key. No manual tuning or
range selection is needed. The modu­lation analyzer automatically tunes
to the input signal, adjusts for proper
signal level, selects the appropriate
measurement range, makes the mea­surement, and displays the result.

High Performance

The HP 8901A Modulation Analyzer
offers a significant advancement in
modulation measurements. Modula­tion depth and deviation are mea­sured with unprecedented 1 percent
accuracy. To complement this capa­bility, optional calibrators with 0.1
percent depth or deviation accuracy
can be included in the analyzer.

A significant improvement has also
been made in the area of residual
noise. The extremely low internal
noise of the modulation analyzer
makes possible residual AM and FM
measurements even on very stable
signals. Accurate measurement of
signals with small incidental AM
or FM modulation are now easily
performed. Residual AM in a 50 Hz
to 3 kHz bandwidth is <0.02 percent,
and residual FM in the same band­width is <8 Hz at 1300 MHz
decreasing to <1 Hz below
100 MHz.

For certain measurements manual
operation may be more desirable.
When selecting a specific signal in
the presence of others or for special
applications, the operator can easily
use the modulation analyzer’s key­board to set any or all measurement
parameters. Functions not selected
manually remain in automatic mode.
This greatly increases the modulation
analyzer’s versatility.

2

The HP 8901A Modulation Analyzer
is a complete measurement system for
accurately characterizing signals in the
150 kHz to 1300 MHz frequency range.

It can make more than just a
single form of measurement; it
combines the capabilities of
three separate instruments. The
HP 8901A Modulation Analyzer
has the capability of a frequency
counter for measuring carrier
frequency. It can measure RF
peak power with typical measure­ment accuracy of ±1.5 dB. It can
also accurately measure modula­tion and recover the modulating
signal. This allows the user to
make those measurements most
commonly needed to totally char­acterize a signal. The modulation
analyzer can measure a signal’s
frequency, frequency drift, peak
power level, AM, FM, or φM, and
AM and FM noise components.
It recovers the modulating signal
with very low added distortion for
audio analysis.

Besides combining several mea­surements in one instrument the
HP 8901A Modulation Analyzer
makes a second contribution to
signal analysis—extremely pre­cise modulation measurements.
Its ability to make highly precise
depth and deviation measure­ments coupled with very low in­ternal noise enables the analyzer
to characterize very accurate
signal sources. Modulation depth
or deviation accuracy is generally
<1 percent of reading. Residual
noise in a 50 Hz to 3 kHz band­width is 0.02 percent for AM and
<8 Hz for FM at 1300 MHz carrier
frequencies, decreasing to <1 Hz
below 100 MHz.

The modulation analyzer is fully
automatic and all major measure­ments can be made by pushing a
single key. The modulation
analyzer’s large digital display
shows measurement results with
excellent resolution and is easy
to read. All measurements can
be easily controlled remotely
and data transferred via the
Hewlett-Packard Interface
Bus (HP-IB).*

Frequency Measurements

In automatic operation the
HP 8901A Modulation Analyzer
has the performance of a high
quality 150 kHz to 1300 MHz
frequency counter. Resolution
is 10 Hz below 1000 MHz and
100 Hz above 1000 MHz. Sensi­tivity is −25 dBm (12 mVrms)
below 650 MHz and −20 dBm
(22 mVrms) above 650 MHz.

Besides normal frequency
measurement capabilities the
analyzer’s counter has several
additional capabilities. Like most
frequency counters it will mea­sure signals over a wide dynamic
range, >50 dB (22 mVrms to
7 Vrms), and is protected from
damage for signals up to 35 Vrms.
Unlike many frequency counters,
however, it automatically adjusts
itself as the input level changes.
There is no need to manually set
or adjust any input attenuator.
Because the modulation analyzer
is usually used to measure modu­lated signals, its frequency
counter accurately measures
signals with significant levels
of AM modulation.

The modulation analyzer uses an
indirect technique for measuring
RF frequencies. Instead of count­ing directly, the input signal is
down-converted to an interme
diate frequency (IF) using a mixer
and a local oscillator (LO). By
counting the frequency of both
the IF and LO and calculating
their difference, the modulation
analyzer can determine the
frequency of the input signal.
In automatic operation the ana­lyzer automatically tunes to the
largest input signal and measures
its frequency.

In manual operation the user de­termines the frequency to which
the modulation analyzer tunes.
When more than one signal is
present it is thus normally pos­sible to select which signal is
counted. Entering the approxi­mate frequency on the keyboard
causes the IF filter to eliminate
all but very close interfering sig­nals. This allows the modulation
analyzer to selectively count sig­nals other than the largest. Also,
because of the large IF gain of the
modulation analyzer, it is possible
to measure very low-level signals.
In manual operation the modula­tion analyzer has sensitivity of

0.22 mV
of >90 dB (0.22 mV

* HP-IB is Hewlett-Packard's implementation

of IEEE standard 488.

, and dynamic range

rms

to 7 V

rms

rms

).

3