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R E S E A R C H into the fields of electrical engineering, physics,
chemistry and all phases of science is greatly aided by the use of
modern electronic measuring devices. The accuracy with which
measurements are made is the yardstick of progress. Time is always
an important element. Thus, electronic instruments should com-
bine speed of operation with accuracy. It was with this idea in mind
that -hp- instruments were developed. In all -hp- instruments the
accent is on speed combined with accuracy. Speed is obtained by
simplicity of operation-accuracy by advanced design and con-
struction.
On the following pages is a comprehensive description of the
-hp- instruments which are now in use by leading organizations
throughout the country. Continual engineering and research in
the -hp- laboratory is resulting in newer developments and addi-
tional instruments to answer the increasing number of problems
encountered in the field of electronic research and production.
Revolutionary Resistance-Tuned P r i n c i p l e
Provides Audio Frequency Oscillators
With Many Outstanding Advantages
T h e purpose of an Audio Oscillator is lator is much more stable and produces less
to generate a stable signal which can be distortion than the common types of vari-
accurately controlled. This signal is used able frequency audio oscillators on the
to check the performance of audio ampli- market today. Low temperature coefficient
fiers, broadcast t r a n s m i t t e r s and other elements in the resistance network keeps
equipment. Minimum of distortion, low thermal drift at the very minimum. Further-
thermal drift and constant output over a more, this thermal drift is not magnified as
wide frequency range are attributes which is the case with the beat frequency oscillator.
such instruments should possess.
A unique balancing circuit automatically
The -hp- Resistance-Tuned Audio Oscil- selects the proper operating point for the
lator utilizes a network of resistors through oscillator and keeps the distortion at a low
which regeneration is supplied. The effec- level a t all times. Thus no manual adjust-
tive "Q' of this network is maintained in ment of the operating point is necessary.
a high order by the negative feedback in The principles of this new development by
the amplifier so that the frequency is stable. the Hewlett-Packard Company a r e dis-
Fundamentally the Resistance-Tuned Oscil- closed in U. S. Patent No. 2268872.
`I
Relatively few circuit elements are required in these Thermal drift is kept at a minimum by low tempera-
oscillators. View above is of sub-chassis. Note the ture co-efficient elements in the resistance network
clean-cut arrangement of the elements and simplicity The frequency is tuned over a 1 0
of wiring in the view of the sub-chassis above. of the variable condenser. The
by selection of the proper resistor with the pan
switch.
The -hp- Resistance-Tuned principle is excellent for many special purposes. The frequency can he
extended several decades to the lower radio frequency range. Because the frequency is stable over 5
long periods, -hp- resistance-tuned oscillators are ideal for operation at very low frequencies. Special
problems in audio or super-sonic oscillators will he given careful attention and the proper instrument
developed to meet your need. Standard Model 200C [above] has a frequency range of 20 cps to 200 kc.
All -hp- instruments are available for relay Special instruments can be supplied in many cases
rack mounting as well as in cabinet models to meet your exact requirements. Above oscillator
Above is Model 200BR resistance tuned Audio a special No. 200D delivers frequencies from 2 cps
Oscillator for relay rack. to 70 kc with a nearly constant output voltage.
6
SIMPLICITY i s
-hp- Instruments are a s Revolution
GAIN speed of operation without sacrifice of accuracy,
all -hp- instruments are designed to operate with a minimum
of adjustment. For the first time a variable frequency audio
frequency oscillator which does not require a zero adjustment
is available. The -hp- vacuum tube voltmeter is as simple to
A Model 205AG is connected to measure the operate as a multi-range d-c instrument.
gain of an amplifier.
The use of audio oscillators is not by any means limited to
the electrical engineering field. One interesting application
of -hp- Resistance-Tuned Oscillators is in the determination
of Young's Modulus of samples of concrete. In this measure-
ment the output of the oscillator is connected to a magnetic
driver to which the concrete sample is secured. The oscilla-
tor frequency is adjusted to determine the resonate frequency
of the sample. From this measurement and other data, the
characteristics of the concrete are determined.
Of course, the large group of applications for -hp- oscillators
is in communications and electronic fields, where the use
and importance of an audio oscillator is well known. Va-
rious oscillators have been designed to meet specific require-
ments generally encountered in this field.
Model 400A is being used for measurements
on a Radio Compass.
Curve below shows the output voltage versus frequency on the model
Below; A Model 205AG is being used on a research project 200C. Note that the frequency response is under 1 DB over 4 decades.
at the Stanford University Communications Laboratory.
7
the KEYNOTE
a s the One-Dial Radio Receiver
Another method -hp- uses to increase the speed of measure-
ment work is to provide equipment to do the complete job
all in one cabinet. The Model 205AG is a good example of
this all-in-one combination of instruments. This instrument
incorporates a resistance-tuned audio oscillator, input meter,
output meter, attenuator and impedance matching system
all in a single unit. This Model 200B oscillator is being used to
check the resonate frequency of a speaker.
The fact that -hp- Resistance-Tuned Oscillators are very
stable makes them particularly suitable for frequency meas-
urements at the lower frequencies. In certain applications it
is important to have the resonate frequency of speaker cones
fall within a very narrow band. Many -hp- oscillators are
made for measurements of this type because the frequency
calibrations can be depended upon over long periods. With
these instruments the inconvenience of continuously re-
adjusting to zero beat is avoided.
In checking frequency of mechanical equipment, these oscil-
lators are invaluable. Such measurements include a wide
range of application from measurements of natural vibra-
tion of mechanical parts to the measurements of output
frequency of rotating equipment, such as generators and
dynamotors.
Frequency of the output voltage of a dyna-
motor is being measured with a Model 200B.
Curve below shows total harmonic distortion vs. frequency on the Model
200C. Note that the distortion is well below 1% over the entire range. Below: Models 205AG and 300A make an
ideal combination for general laboratory use.
For Distortion Measurements
TWO types of -hp- instruments are available for
distortion measurements, the 300A and 320 series.
Model 300A is a tuned voltmeter and its primary
purpose is to measure the individual components
of a complex wave. This instrument is also useful
in analyzing vibration components in a mechanical
system. It is useful in making performance meas-
urements on wave filters and in many other
applications where the exact voltage of a particu-
lar frequency is to be measured.
Where measurements of the total harmonic dis-
tortion present are required, the 320 Distortion
Analyzer provides a simple and direct answer.
These analyzers are most useful instruments in
development work on audio frequency systems.
When used in combination with an oscilloscope,
a direct picture of distortion components can be
obtained while circuit changes are being made.
Where the problem is production testing, these
analyzers provide the quickest means for making
8 distortion measurements.
Model 300A Wave Analyzer being used to measure
the individual harmonics present in the output volt-
age of an amplifier.
Model 320B Distortion Analyzer is easy to operate The 325B Distortion Analyzer i s bring used to mea-
and provides a rapid and accurate check of distortion sure the total harmonic distortion of a Model 200B
in audio frequency apparatus. on the production test bench.
The S q u a r e W a v e M e t h o d
O N E of the most recent approaches to the problem
of measuring the response of amplifiers and net-
Square Wave Distortion from poor high frequency works is to apply a square wave voltage and
response. observe shape of t h e wave which is transmitted. A
sharp wavefront contains a large number of fre-
quencies. This wavefront is distorted when all of
the frequencies originally present are not trans-
mitted. The frequencies contained in a uniform
square wave are given by the relation:
wt 3 + 1/5 sin 5 wt
In practice a wave which appears to he perfectly square
will contain thirty harmonics or more and when the ampli-
Square Wave Distortion from poor low-frequency tude or phase relation of the harmonics is disturbed the
sponse. (Phase shift of law frequency components wh square wave will he distorted.
always accompanies cut-off.)
Thus the application of a square wave to a circuit shows up
any irregularities in the amplitude or phase transmission
of that circuit not only at the square wave frequency but
also at frequencies far removed from the test point.
Because a square wave observation will indicate circuit
performance over a wide frequency range in one observa-
Square Wave Distortion f r o m poor response at both low tion, it is a very important test to use with other standard
and high frequency (A typical amplifier oscillogram.) point by point measurements which are often not sufficient
alone.
The square wave test is particularly important in feedback
circuits where the circuit performance outside the normal
transmission hand is generally of interest. The application
of a square wave test to a feedback amplifier will show in
a single observation whether the amplifier is close to the
oscillation point.
Both as a general purpose instrument for laboratory work
and as a time saver in production testing a square wave
Square Wave test on a feedback amplifier showing ampli-
fication peak at 9 times square wave frequency A normal generator is an important instrument in the electronic
frequency response measurement shows flat response field.
from 20 cps to 20KC)
The -hp- model 210 Square Wave Generator provides an
excellent square wave and is more useful than other in-
struments of this type because the frequency can he accu-
rately set for quantitative measurements of decrement fac-
tor, time and other quantities in transient analysis.
Attenuator leakage a t high frequencies shows up in this
oscillogram.
Square wave applied t o two amplifiers, output of one on Came as left. One amplifier defective shows up immedi-
horizontal plater, output or other vertical plates for rapid ately whereas without square wave a long point by point
comparison test. Nearly straight line obtained when am- frequency response would be required to discover devia-
plifiers have nearly identical characteristics. tion from standard.
9
Accurate Voltage Measurement
OF the many electronic instruments, one of the
most useful is the Vacuum Tube Voltmeter. There
are many types available today, most of which
have certain important features in common, two of
which are . . . high input impedance and wide
frequency response.
High input impedance is a feature not obtainable
in an ordinary A . C . voltmeter. This important
characteristic is obtainable in an electronic volt-
meter. It enables one to measure voltage without
disturbing the current under test. The wide fre-
quency response which can be obtained makes it The 400A is unexcelled for production applica-
tions such as these shown; where accurate high
possible to measure voltage at high frequencies frequency measurements can be made without
with good accuracy. High sensitivity and good particular precautions.
accuracy are other characteristics highly desirable
for laboratory and production work.
The -hp- Model 400A Vacuum Tube Voltmeter,
a recent development of the -hp- laboratories, pos-
sesses all the important desirable features. It is one
of the best available for measurements below 1
megacycle.* It is extremely easy to operate, yet its
accuracy is unexcelled and it has extreme sensitiv-
ity over a wide frequency range. One of the
outstanding features of the -hp- 400A is that the
voltage indication is proportional to the average
value of the full wave. This is a feature not found
in most electronic meters on the market today.
*At frequencies above 1 megacycle the dipole voltmeter
is generally satisfactory. If properly designed it will
provide good accuracy t o 100 mc, but with some sacrifice
Of sensitivity
10
M O D E L 200C
RESISTANCE-TUNED A U D I O O S C I L L A T O R S
Low distortion N o zero setting
e Constant output a Small size
e Logarithmic scale High output
USES : Resistance-Tuned Oscillators are suitable for
almost every type of work. Their low distortion makes
them particularly valuable in making distortion measure-
ments on audio amplifiers, broadcast transmitters, and
other equipment. They provide an excellent source of
voltage for accurate bridge measurements. The output is
sufficient to drive signal generators and other equipment
requiring considerable power. Their wide frequency
range also makes them suitable for work in the super-sonic Arrangement beneath chassis gives goad accessi-
bility to all parts.
region.
Top of chassis view showing main tuning condenser.
There are only three controls on the panel: the main
frequency dial, the range selecting switch, and the output
voltage control. The usefulness of Resistance-Tuned
Audio Oscillators is increased because they are small in
size and light in weight. Their extreme simplicity of op-
eration will save valuable time in production testing,
maintenance, and development work. The frequency
drift is negligible even during the first few minutes of
operation and consequently no zero adjustment is nec-
essary. The constant output of these oscillators makes
it easy to check the frequency response of apparatus
quickly and accurately.
11
200B and 200C frequency 200D frequency Model 200D
control dial. control dial.
SPECIFICATIONS: The Hewlett-Packard oscillators tions change the frequency less than ?O.Z% at 1 kc.
are designed and built to give long, trouble-free No zero setting is necessary on these oscillators.
service. High quality parts are used throughout, and OUTPUT: The Models 200A and 200B will supply
each oscillator is subjected to rigid tests before ship- one watt output into a matched resistance load of 500
ment. Four standard models are available. The Models ohms, 25 volts on circuit. special imped-
200A and 200B have a transformer-coupled output ances can be supplied order,
amplifier which will deliver 1watt into a matched load.
The Models 200C and 2OOD have a resistance-coupled The de'iver lo
output amplifier uniform voltage into a 1000 ohm load. The internal impedance of the
over their wide frequency range. These oscillators are Output amp1ifieris about 50 Ohms at 'Oo0 'pS.
supplied in a relay rack mounting as the 200AR FREQUENCY RESPONSE: The output voltage of
200BR 200CD and 200DR respectively. the Models 200A and 200B is constant within plus or
FREQUENCY RANGE: minus 1 decibel from 20 cps to 15 kc.
Model 200A............................................ 35 cps to 35 kc The output voltage of the Model 200C is constant
Model 200B............................................. 20 cps to 20 kc within plus or minus 1 decibel from 20 cps to 150 kc.
Model 200C............................................ 20 cps to 200 kc The output voltage of the Model 200D is constant
Model 200D............................................ 7 cps to 70 kc within plus or minus 1 decibel from 7 cps to 70 kc.
CALIBRATION: The dial is calibrated directly in DISTORTION: The total r.m.s. distortion contained
cycles for the lowest range. A switch selects the range in the wave-form of the various models is within the
and indicates the proper multiplying factor. Each range following limits : Models 200A, 200B, less than 1 %
covers 180 degrees on the dial and so the equivalent distortion from 35 cps to 20kc. Model 200C, less than
scale length is from 20 to 30 inches on the various 1% distortion from 20 cps to 20kc. Model 200D less
models. than 1% distortion from 10 cps to 20 kc.
200A 200B HUM VOLTAGE: The hum voltage is less than O.lvo
Range 1..........
.......... 35.350 cps................20-200 cps of the maximum output voltage.
Range 2 ..........
.......... 350.3500 cps............ 200-2000 cps
Range 3..........
.......... 3500 cps-35 kc.......... 2000 cp~-zo kc POWER SUPPLY: 115 volts-60 cyc1es-50 watts.
200C 200D TUBES: Models 200A and 200B 1 6J7, 1 6F6, 1 6F5;
Range 1.......... 2 0.200 cps................. 7-70 cps
.......... 16V6, 1 5Z4 Models 200C and 200D 2 6J7, 1 6F6,
Range 2 ..........
.......... 200.2000 cps............70-700 cps 1 6V6,15Z4
Range 3..........
.......... 2000 cps-20 kc..........700-7000 cps MOUNTING: The cabinet models are mounted in
Range 4................~~..20 kc-200 kc.............7000 cps-70 kc an attractive steel cabinet finished in wrinkle grey.
STABILITY: Under normal temperature conditions The relay rack mounting fits the standard 17" relay
the frequency drift is less than kzy0 even including rack with 3/" spacing. The dust cover mounts on the 1
initial warm-up. Plus or minus 2oyoline voltage varia-
Model Mounting Length
chassis and is removable from the rear.
Height Depth Weight
s
200A Cabinet 16" 8" 9" 32#
200B Cabinet 16" 8" 9" 32 #
200C Cabinet 16!< 8" 9" 30#
200D Cabinet 19" 83/" 11"' 32#
200AR Relay Rack 19" 7" 7" 35#
200BR Relay Rack 17'' 7" 9" 35#
200CR Relay Rack 19" 7" 9" 35#
200DR Relay Rack 17" 8y4" 11" 37#
Data subject to change without notice.
H HEWLETT-PACKARD C O .
395 PAGE MILL ROAD, PAL0 ALTO, CALIFORNIA
12
M O D E L 205AG
A U D I O S I G N A L GENERATORS
MODELS 2 0 5 A A N D 2 0 5 A G
Y
e Stuudurdized frequencies and voltage instantly
available
Output impedances selected by switch
e Attenuation system provides 110 db. in 1 db. steps
Five watts output with less than 1% distortion
e Frequency always accurate without zero setting
e Output meter calibrated in volts and decibels
e Separate input meter available f o r gain measure-
ments
USES: The Hewlett-Packard Audio Signal Generators
are designed for time saving performance. The various
features have been selected with the aim to make these
instruments suitable for accurate and rapid measurement
1, work. They are excellent for general laboratory applica-
tions because they supply a known voltage as well as a
Views of bottom and tup of 205A
t known frequency at the commonly used impedance levels.
They are particularly suitable for gain measurements
because no auxiliary apparatus is required. They provide
an excellent source of voltage for distortion measurements
because their waveform distortion is very small. The many
new features make these instruments adaptable to numer.
ons jobs in the audio frequency field.
DESCRIPTION: The Model 205A consists of a Hewlet-
Packard resistance-tuned oscillator in combination with
an output meter, attenuator, and an impedance matching
system. The Model 205AG includes input meter for gain
measurements.
The accompanying block diagram shows the arrange-
ment of the various components in the system. The
13
oscillator has a five-watt output which feeds directly
into a 500 ohm line where the voltage is measured. The
amplitude of this voltage can be set to any level up to
plus 37 decibels above one milliwatt by means of the
amplitude control on the oscillator. Following the
meter are two attenuators, one providing 100 decibels
in 10 decibel steps and the other providing 10 decibels
in 1 decibel steps. From the output of the attenuators
hl9h.,lp.dwm `q"pm"I
an impedance matching transformer is provided to 205AG input and 205A frequency
output meters. control dial.
match various impedances. The output transformer has
the same insertion loss for all impedances and the Every precaution has been taken to make these signal
output meter is arranged to read the output voltage at generators precision instruments. Special heavy me-
the output terminals with the system loaded. An chanical construction has been used throughout to give
internal load is provided so the attenuation system assurance that the accuracy will he maintained in long,
works correctly when there is no external load. hard service.
SPECIFICATIONS
Model 205A OUTPUT METER: The output meter is calibrated
directly in volts at 500 ohms and in db. above a 1mw.
FREQUENCY RANGE: The frequency range i 20
s level (50 volts and plus 37 db. full scale).
cps to 20,000 cps.
OUTPUT ATTENUATOR: The output attenuator
CALIBRATION: The dial is calibrated directly in provides 110 db. in 1 db. steps. It consists of a 100 db.
cydes for the lowest range, 20 cps to 200 cps. A switch attennator with 10 db. steps and a 10 db. attenuator
selects the range and indicates the proper multiplying with 1 db. steps.
factor. Each range covers approximately 270 degrees
MOUNTING: The instrument is available in either
on the 6$5" main dial. Range 1 covers 20 cps to 200 relay rack or cabinet mounting, the panel size on either
cps; Range 2 covers 200 cps to 2,000 cps; and Range 3
instrument is 19" x 10%". The cabinet models are
covers 2,000 cps to 20,000 cps. mounted in attractive oak cabinets finished to harmon-
STABILITY: Under normal temperature conditions ize with the panels. The panels are finished in gray
the frequency will drift less than 2% over long periods wrinkle enamel with machine engraved designations.
of time. Each range is provided with an internal adjust-
ment so that 1% accuracy may he maintained if re- Model 205AG
quired. The Model 205AG is exactly similar to the Model
205A except it has an input meter for gain measure-
OUTPUT: Five watts output will he delivered to a ments.
matched resistance load.
INPUT METER: The input meter has a range of
OUTPUT IMPEDANCES : Output impedances of 50 minus 5 dh. to plus 49 db. based on a 1 mw. level and
ohms, 200 ohms, 500 ohms, and 5,000 ohms are avail- 500 ohms. The meter scale is calibrated from minus
able. All are center tapped. 5 db. to plus 9 db. and a multiplier switch adds from
zero to 40 db. to the reading in 5 db. steps. The meter
FREQUENCY RESPONSE : The frequency response has an impedance of 5,000 ohms.
of the system beyond the output meter is down 2.0 db.
at 20 cps and 1db. at 20,000 cps. FREQUENCY RESPONSE : The input meter is com-
pensated to have about 0.5 db. rise at 20 kc so that
DISTORTION: The distortion is less than 1% at full gain measurements with the Model 205AG are accu-
output at all frequencies above 30 cps. rate to 15 kc and only ahout 0.5 db. in error at 20 kc.
Prices and delivery information are available on re-
HUM LEVEL : The hum level is 60 db. below the out- quest.
put voltage or minus 90 db. below zero level, which-
ever is the larger. These data are subject to change without notice.
HEWLETT-PACKARD C O .
395 PAGE MILL ROAD PAL0 ALTO, CALIFORNLA
14
VACUUM TUBE
VOLTM E T E R
MODEL 400A
8 W i d e voltage range 8 Time saving stability 8 Good voltage sensitivity
8 Excellent accuracy 8 High input impedance 8 Large overvoltage capacity
USES: The Model 400A Vacuum Tube Voltmeter sets a new
standard of performance for voltage measurements in the audio,
supersonic, and lower radio frequency region. Measurements up to
1 megacycle with this new instrument are as simple as measurements
with the usual multi-range meter at d-c. Ordinarily no precautions
whatsoever are required: turn-over effect and waveform errors are
minimized because this meter responds to the average value of the
full wave; there are no adjustments to make during operation; a large
overload will not damage the instrument; and the input impedance
is high enough so that it will not affect the circuit being measured.
The excellent characteristics of this meter make it invaluable for
Circuit elements arc rigidly mounted on laboratory work in measuring amplifier gain, network response, out-
Bakelite cards to assure dependability. put level. The sensitivity is sufficient to measure the hum level directIy
View below shows tube arrangement
on top of chassis. in many cases. The high voltage ranges are useful for measuring
power circuit voltages and high frequency voltages in transmitting
equipment. A decibel scale is previded to facilitate readings in cases
where a decibel base is desired.
The simplicity of operation of the Model 400A will save valuable
time in production testing because no time will be lost in adjusting
the zero position or in making other adjustments during operation.
The usefulness of this instrument is increased because of its wide
frequency range. It is ideally suited not only for audio frequencies
from 10 cps to 20 kc, but also for applications in carrier current work,
in supersonics, in television and throughout the broadcast field.
15
DESCRIPTION: The Model 400A Vacuum Tube Voltmeter is a
wide band feedback amplifier which operates a diode voltmeter of
the average reading type. The circuit is independent of line voltage
variations and tube characteristics to a high degree. A special input
amplifier circuit is used to provide a high input impedance and also
to allow the use of an accurate voltage divider to select the voltage
range. The power supply is self contained, thoroughly filtered and
electrostatically shielded from the primary voltage source.
Range selection switch on 4OOA. Note
both voltage and D. B. calibrations.
The instrument i s mounted in a metal cabinet finished in wrinkle
grey. The meter scale is on a sloping panel to facilitate meter read-
ings. The scale is calibrated in volts and decibels. Because of the
design of the instrument reasonable overload voltages will not
damage the meter movement.
The small size and light weight of this meter combine with its excel-
lent characteristics to make it a real time saver in the laboratory or
Meter face an 400A. Note both voltage
in the field. and D. 8.calibrations.
SPECIFICATIONS
VOLTAGE RANGE: A switch on the front panel INPUT IMPEDANCE: The input impedance is
selects nine voltage ranges having full scale sensitivi- equivalent to 1 megohm shunted by 16 nufd.
ties of .03 volts, 0.1 volts, 0.3 volts, 1.0 volts, 3.0 volts,
10.0 volts, 30.0 volts, 100 volts, 300 volts. OVERVOLTAGE CAPACITY: Occasional overloads
of 100 times normal will not damage the meter move-
CALIBRATION: The meter is calibrated to read the ment. Continuous or frequent overloads should he
r.m.s. value of a sinusoidal wave. The voltage scale is avoided.
linear and a decibel calibration based on 1 milliwatt
and 600 ohms i s provided. The indication is in prop&-
POWER SUPPLY: The instrument operates from 115
tion to the average value of the full wave, thus wave-
volts 60 cps.
form errors and turnover are minimized.
FREQUENCY RANGE: The frequency response of MOUNTING : The meter i s mounted in a steel cabinet
the meter i s within 3% from 10 cps to 100 kc and finished in wrinkle grey. The front panel is heavy
within 5voto 1MC. brass finished in satin chrome plate with photo-etched
designations. The cabinet i s 79" inches wide, 8 inches
ACCURACY: The over-all accuracy of the meter is9yo high, and 9 inches deep. A leather handle is provided
below 100 kc and 5y0 from 100 kc to 1.0 MC. Line volt- at the top of the cabinet.
age variations from 105 volts to 125 volts or changing
tubes will affect the reading by less than 3y0 at all SHIPPING WEIGHT: 20 pounds.
frequencies helow 100 kc. Data subject to change without notice.
H EWLETT-PACKARD CO.
395 PAGE MILL ROAD PAL0 ALTO, CALIFORNIA
16
HARMONIC
WAVE
ANALYZER
MODEL 3 0 0 A
A New Wave Analyzer Featuring
e Linear meter scale Simplified operation
0
Improved stability Q Variable selectivity
W i d e voltage range
USES: The many new features o the Model 300A Harmonic Wave
f
Analyzer make it an excellent instrument for both laboratory and
production work where accurate and rapid measurement of indi-
vidual components of a complex wave is required.
The maximum selectivity is sufficient for measurement of harmonics
of frequencies as low as 30 cycles. Furthermore, the selectivity can
be varied over a wide range by means of a unique selective amplifier
developed in the Hewlett-Packard laboratories. With this variable
selectivity feature, measurements at higher frequencies can he made
more rapidly, yet with no sacrifice in accuracy.
Above: A 74ew from rear of 300.4. Variable selectivity makes this analyzer useful for many applications
Below: A positive dial control. where a constant selectivity would he unsuitable. For example, vari-
able selectivity is required in measuring distortion of sound recorded
on film, disk, or other cases where there may he a small amount of
frequency modulation. It may be used in integrating the noise spec-
trum for acoustic measurements or for other purposes where a wider
pass hand gives a more representative integration. In many other
ways the usefulness of the Model 300A is increased, because the selec-
tivity can be varied at will.
The wide voltage range of the Model 300A covers the values encoun-
tered in nearly every application. The meter, which is fully protected
against overloads, is linear, and the various scales have ample overlap
for accurate readings. A built-in calibrating system is provided to
standardize the voltage measurements.
The accuracy, stability, flexibility, and ease of operation of this new
wave analyzer assure time-saving performance for any application
requiring a frequency-selective voltmeter.
17
DESCRIPTION: The Model 300A is a frequency.
selective voltmeter of the heterodyne type. It consists
of a variable local oscillator which modulates the
unknown voltage to produce a constant frequency
which is equal to the difference between the local oscil.
lator frequency and the unknown frequency that is
being measured. This constant difference frequency is
passed through a selective amplifier, the output voltage
of which is then proportional to the magnitude of the
unknown voltage. A meter is placed in the output of
the selective amplifier to measure the magnitude of the
voltage.
The local oscillator is of the resistance-tuned type
which provides stability, accuracy of calibration, and
freedom from magnetic fields. A balanced modulator
is used to eliminate the local oscillator frequency and
to insure low cross-modulation products. The selective Close-up of main tuning dial. Direct reading.
amplifier consists of four tuned circuits in which the
effective Q is controlled by feedback. This amplifier At the bottom of the main panel are the balancing and
has the unique characteristic that the selectivity may he calibrating controls and a calibrating meter which is
varied over a wide range without appreciably affecting used to check the sensitivity against the line voltage.
the gain of the amplifier. These controls are mounted in a small, recessed com-
partment which may be closed during normal opera-
On the front panel are the main frequency selecting tion.
dial, an incremental frequency dial for fine adjustment, The instrument has been designed throughout for ease
variable selectivity control, meter, range selectors, and of operation and for accuracy which will be maintained
input control. over long periods of time.
SPECIFICATIONS
FREQUENCY RANGE: The frequency range is from VOLTAGE ACCURACY: The over-all voltage accu-
30 to 16,000 cps. The frequency calibration is within racy is is%, provided adjacent harmonics are within
3%. limits determined by the selectivity. The characteristics
VOLTAGE RANGE : There are four input voltage of the metering circuit are such that measurement of
ranges having maximum values of 0.5 volts, 5 volts, a particular component may be made with 5% accuracy,
50 volts, and 500 volts. In addition, a meter multiplier provided unwanted voltages are attenuated to less than
divides each voltage range into full scale meter readings v3 of the voltage being measured. Thus, with max-
of 500, 250, 100, 50, 25, 10, 5 , 2.5, and 1. Thus full imum selectivity a 1% second harmonic of a 40 cycle
scale meter readings can he obtained on from 1 mv voltage may be measured with 5T0 accuracy.
._
to 500 v. The meter is linear and is fully protected The residual modulation products are suppressed by
against overloads. at least 65 dh. Hum is at least 75 db. below maximum
SELECTIVITY: The selectivity can be varied by input voltage on any of the four input ranges.
means of a control on the front panel. At the max- INPUT IMPEDANCE: The input impedance is
imum selectivity setting, the response is down 3 dh. at
3 cycles, 10 db. at 8 cycles, 40 db. at 30 cycles, and 200,000 ohms. The input circuit includes a potentio-
meter which is set to maximum for voltage measure-
60 db. at 50 cycles from maximum response. This selec- ments.
tivity can he varied continuously until at the minimum
selectivity the band width required for a given attenua- POWER SUPPLY: The instrument contains a volt-
tion is six times that at the maximum selectivity set- age regulated power supply which operates from 110
ting. Thus, at minimum selectivity the response is volts, 60 cycles.
down 3 dh. at 18 cycles, 10 db. at 48 cycles, 40 db. at MOUNTING: The Model 300A is mounted in an
180 cps, and 60 db. at 300 cycles from maximum re- attractive oak cabinet to harmonize with the panel
sponse. The variable selectivity control is calibrated which is finished in wrinkle grey with machine en-
in the half band width at which the reqonse is down graved designations. A relay rack model is also avail-
40 db. able and is designated as the Model 300AR.
~
Model Mounting Length Height Depth Shipping
Weight
300A Cabinet 21" 241/7" 13" lSO#
300AR Relay Rack 19" 22% 12" 170#
These data are subject to change without notice.
H EWLETT-PACKARD CO.
395 PAGE MILL ROAD, PAL0 ALTO, CALIFORNIA
18
s DISTORTION ANALYZER
A new inzrument for distortion measurements
0 Shows type of distortion as well as amount
Standard models for measurements at two or
six frequencies
USES: The Model 320 Distortion Analyzer is a
THE M O D E L 320B
Any frequencies from 50 to 10,000 cycles
available
Saves time in development and production
testing
simple and convenient device for studying and mea-
suring the harmonic distortion in audio frequency ap-
paratus. It is particularly suitable for development
work because with it the character and type of distor-
tion can be determined at the same time the distortion
is being measured. It is excellent for production work
because it is easy to operate and provides a rapid and
accurate check for normal operation.
The Model 320 is essentially a comparison device used
to compare the distortion content of the wave with
the fundamental voltage. When this comparison is
made with a cathode ray oscilloscope the type of dis- Views showing bottom and top of 320B chassic.
tortion can be observed. The various order harmonics
will show up on the oscilloscope pattern, the hum volt-
age and noise voltage will appear, and a great deal of
information ahout the voltage being analyzed can he
obtained. In this way the Model 320 is a valuable in-
strument not only when used alone hut also when used
with other equipment which measures the total r.m.s.
distortion directly.
1)ESCRIPTION: The distortion an;iljzer c o n d s of
two fundnmmtal elimination filturs, one for measiire-
intnts nr 400 cycles and one fur meii\urunient, IC 5,000
c!,clci, and B c3libr~tcd
atrenuitor. U'ith the volt?qc to
19
be analyzed adjusted to the proper frequency the funda-
mental is eliminated completely. The residual voltage
containing the harmonics can then be observed with
an oscilloscope or measured with a sensitive meter.
When the frequency has been adjusted so the funda-
-
I EQUIPMENT
UNDER
TEST
I
400.
200 C 320 E A
mental is eliminated, the elimination filter is switched
out and a calibrated attenuator is introduced. II
MEASUREMENTS : With the proper adjustment, the
setting of the attenuator on the instrument gives
l
h
directly the amplitude of the harmonic voltage in deci-
bels below the fundamental. When an oscilloscope is
used for the detector, measurements of the harmonic ments may be made with as good accuracy as can be
voltage require some exercise of judgment. The resid- obtained with the more expensive distortion meters.
ual harmonic voltage will contain sharp peaks in many For distortion analysis an oscilloscope should be used
cases. These peaks contain very little energy and this as the detector. As the frequency is adjusted to elimi-
should be taken into account in estimating the r.m.s. nate the fundamental, the second, third, and higher
or average value of the residual harmonic voltage. order harmonics will appear superposed on the fun-
If more accurate measurements are desired a meter damental voltage, and from the trace obtained the
may be used in place of the oscilloscope or in conjunc- relative importance of these components can be deter-
tion with it. With such a meter the distortion measure- mined.
SPECIFICATIONS
FREQUENCY RANGE :The Model 320A is designed damental if harmonics of 0.17' are to he measured.
for measurements at 400 and 5000 cps. The Model 320B The detector need not be calibrated because it is used
is designed for measurements at 50, 100, 400, 1000, for comparison only. The usual oscilloscope with a
5000, and 7500 cps. Filters for other frequencies can one stage amplifier is sufficiently sensitive tn measure
be supplied on special order. 0.3V0 of a 30 volt fundamental. For proper operation
of the instrument the input impedance of the detector
INPUT IMPEDANCE: The input impedance is at must be 100,000 ohms or greater. An amplifier may
least 20,000 ohms. A bridging transformer may be be used between the instrument and the detector to
used to increase the input impedance. increase the sensitivity. The only requirements on such
an amplifier are that it must pass the highest harmonic
DISTORTION RANGE: The filter circuits will pro- which is of interest and that it have a high impedance
vide more than 60 db of attenuation of the funda- input. It need not be free from distortion otherwise.
mental, Distortion values as low as 0.17' of the funda-
mental may be measured with a detector of sufficient M O U N T I N G : The Model 320A and 320B are
sensitivity. mounted in an attractive oak cabinet with the panel
finished in wrinkle grey. The Model 320AR and 320
DETECTOR SENSITIVITY: The sensitivity of the BR fit the standard 19" relay rack with y4"spacing.
instrument is determined by the detector. The detector The panels are finished in wrinkle grey with machine
should give a readable indication on 0.17' of the fun- engraved designations.
Model Mounting Length Height Depth Weight
320A Cabinet 12" 8" 6" 8#
320AR Relay Rack 19" 51& 9'
55' S#
320B Cabinet 16" 8" 6" 15#
320BR Relay Rack 19" 7" IO'' 20#
Data subject to change without notice.
H EWLETT-PACKARD CO.
395 PAGE MILL ROAD PAL0 ALTO, CALIFORNIA
M O D E L 325B
NOISE AND DISTORTION ANALYZER
The Model 325B combines a vacuum-tube voltmeter
with a set of fundamental elimination filters for general
purpose measurements of total harmonic distortion, noise
and voltage level.
USES: The Model 325B provides a new approach to
the problem of audio frequency measurements. The instru-
ment can be used as a voltmeter for measuring voltage
level, power output, amplifier gain, and in making all
of the other measurements for which a high impedance
voltmeter with a wide frequency range is necessary.
Sufficient sensitivity is available in the Model 325B to
measure noise and hum level in audio frequency equip-
ment such as amplifiers and broadcast equipment. With
the addition of a detector, noise level in the carrier out-
put of transmitting equipment can be measured.
View rhowing arrangement of components o s chassis.
A set of fundamental elimination filters is included in
the instrument to measure total harmonic distortion at
nine specific frequencies. These are the frequencies recom- Wiring is located below charrir fay accessibility.
mended by the FCC for measurements on Freuencymod-
ulation as well as amplitude modulation equipment. On
special order, filters for other frequencies from 30 cps
to 20KC can be supplied. The amplifier and voltmeter
section is flat from 10 cps to l00KC so that harmonics
as high as the 5th of 20KC will be correctly indicated.
The Model 325B will meet the requirements of the
most exacting production test problem on audio frequency
equipment and when combined with a -hp- resistance-
tuned Oscillator all of the measurements usually required
on audio equipment can be made quickly and accurately
with a minimum of additional equipment.
DESCRIPTION: The Model 325B consists of three
separate sections, an input amplifier, a set of frequency
elimination filters, a vacuum-tube voltmeter. A voltage
21
The input amplifier has a gain which is set by feed-
back to exactly 20db. This amplifier can be connected
direrrlv tn the voltmeter section or it can be connected
.. , -
- . ..~
to the voltmeter through the elimination filters. This
provides a high input impedance for distortion mea-
surements and additional sensitivity for hum and noise
measurements. A potentiometer is provided at the in-
put for convenience in setting level.
The elimination filters are of the bridged T type for
which the frequency to be analyzed must be variable
over a range of 10vo When the frequency is properly
set the fundamental elimination is almost complete
so that distortion as low as O.lvocan be measured with
good accuracy. Special precautions have been taken tn
., . .... . ... ......
.
permit good &;racy iA distortion measurements even
at 2OKC.
Voltmeter Face. Note borh voltage and
The vacuum-tube voltmeter section is a two stage 1).B. calibrations.
amplifier with feedback to insure stable operation.
It is identical with the Model 400A voltmeter except The multitude of ways in which this instrument can
the frequency range is limited to 100KC. Terminals be used make it almost indispensable for laboratory,
are provided at the meter output for waveform obser- production test, or maintenance applications in the
vations with an oscilloscope. audio frequency field.
SPECIFICATIONS
S E N S I T I V I T Y : The Model 325B will give full higher harmonics by less than 5%. Distortion measure-
scale indication on a distortion level which is 1% of ments in general will he accurate with k 3 v 0 for dis-
the fundamental. Measurements to 0.1 yomay be made tortion levels above 0.5%. When the distortion is
with good accuracy. largely second harmonic the accuracy will be t59&
The instrument will give a full scale indication on for frequencies above 7.5KC.
hum and noise which is 0.01% of the signal. The full NOISE MEASUREMENT ACCURACY: The ac-
scale sensitivity is 3.0 millivolts or 50db below 1 mw curacy of noise and hum measurements is essentially
on 600 ohms. Satisfactory readings to 70db below zero the same as the accuracy of voltage measurements. The
can he made. The over-all gain from the input fer- measured value is the average value of the full wave.
minals to the oscilloscope terminals is 75 dh. INPUT IMPEDANCE: The impedance at the input
VOLTMETER RANGE : Nine voltage ranges are amplifier terminals is approximately 200,000 ohms
provided with full scale sensitivities of .03, .lo, .30, shunted by approximately 24 unfd. The input impe-
1.0, 3.0, 10, 30,100, 300. The ranges are also calibrated dance at the meter terminals is 1 megohm shunted by
in db and the range multiplier changes the sensitivity approximately 32 uufd.
in steps of exactly 10. db. Zero level is 1 mw across, GENERAL: The Model 325B is complete with all
600 ohms. necessary power supplies for operation from 115 volts
VOLTMETER ACCURACY: The over-all accuracy 60 cycles. The various parts of the unit are arranged
of the unit for voltage measurements is 3% Line volt- for maximum flexibility so they can be used separately
age variations from 105 volts to 125 volts or changing
I -
if desired. A lug is supplied to connect an oscillo-
& . ,
tlbes affectsthe reading by less than 3%. scope across the metering circuit so that observations
VOLTMETER FREQUENCY RESPONSE : ~h~ fie- of the residual distortion may be made if desired. The
qnency response of the including the input am. indicating meter is a 4-inch square type with a large
plifier is within 3 0from 10 cps to 100 KC.
v scale for ease of reading. The meter and various range
switches are calibrated in both volts and decibels. In
FILTER FREQUENCY: Filters are provided for the general the instrument is designed for accuracy and
following frequencies : ease of operation.
30 cps, 50 cps, 100 cps, 400 cps, 1000 cps,
5000 cps, 7500 cps, 10,000 cps and 15,000 cps.
MOUNTING: The unit is mounted in an attractive
oak cabinet with the front panel 19 inches by 10%
These freqnendes are set to * 5 % Of SPedfied
inches, Complete shielding is provided against pickup
DISTORTION MEASUREMENT ACCURACY: The from either 60 cycle or r. f. fields of reasonable mag-
filters are designed to eliminate the fundamental by nitude. The panel is finished in wrinkle grey enamel
more than 60 db and to attenuate the second and all with all controls and ranges dearly marked.
H EWLETT-PACKARD C