t^ HEWLETT'PACKARD
. ® JOURNAL
y Jb"^ technical information FBOM the -hp- LABORATORIES
VOL. 3 No. 4
'UBLISHED BY THE HEWLETT-PACKARD COMPANY, 395 PAGE MILL ROAD, PALO ALTO, CALIFORNIA DECEMBER, 1951
Oscillators for Many Purposes
WHEN need arisies for a test oscillator,
at least one characteristic of the
needed oscillator is automatically known.
Usually, this known characteristic is the fre-
quency range. In many cases, however, need
for an oscillator involves other characteris-
tics as well as frequency range. Power out-
put, output impedance, distortion, and dial
resolution are all determinitig factors for
som e a p p I i c a t i on s .
The 'bp- series of test oscillators includes
some 16 separate instruments. Collectively,
these oscillators operate from 0,01 cps to 10
megacjxies, covering the audio, sub-sonic,
ultra-sonic, and iow^ r-f regions. Several of
the instruments are general-purpose types,
designed to operate over wide frequenc>^
ranges and to provide generous output volt*
ages. Others are designed for particular
types of applications. In the accompanying
table (next page) the oscillators are classified
according to their principal distinguishing
features. Where appropriate, some of the
Fi^. L -i?p' Madet^ 630 A Test Oscilli/ior operates from 10 cps io W megticyclei,
Siep-atienuator conirois Hftipui power*
oscillators are listed under more than one
classification.
These 16 -hp- test oscillators are separate
from the -hp- series of audio signal genera-
tors which, in general, are distinguished by
high output powers, by the ability to gener-
ate accurately-known power levels, and by
the abilit\' to generate very low audio levels.
When first introduced, the -hp- resistance-
capacity' oscillator quickly gained leading
popLiIarit)' because of its wide frequency
range, high stability', and low distortion.
The -/>/?- Models 200A, 2()()B, and 200C
oscillators were the first commercial test
oscillators constructed using the now well-
known R-C oscillator circuit* The 2 00 A op-
erates from 35 cps to 35 kc; the 200B from
20 cps to 20 kc. Both instruments deliver one
watt to a 500'ohm load and can be used with
any higher-Impedance load without deterio-
ration of characteristics. The -hp- Model
200C operates from 20 cps to 200 kc and
provides 10 volts to J 000 or more ohms.
Need for an oscillator to cover a
range from well below to well
above the audible range led to
the development of the Model
200D, which operates from 7 cps
to 70 kc and also provides 1 volts
to a load of 1 000 or more ohms.
The 'bp- general-purpose group
of oscillators includes the above
four instruments and the Model
650 A, The 650A generates the
highest frequenc)' of any of the
-bp- series of R-C oscillators. It
operates up to 1 megac> cles and
down to 1 cps— a range of one
^HINTEO fN U.S.A.
COPTBIGMT »951 MKWfLETT ■ PACKARD CO.
)Copr. 1949-1998 Hewlett-Packard Co.
-hp-
TEST OSCILLATORS
GENERAL HIGH LOW
PURPOSE FREQUENCY FREQUENCY
BATTERY*
OPERATED
PORTABLE
\™ HIGH
DISTORTION RESOLUTION
CARRIER
TEST
200A 650A
200B 200C
200C 200H
200D (See also
650A "Carrier TesH
200D
202A
2028
202 D
204A
204A
201 B
2001
200H
230A
23IA
2 32 A
233A
million-to-one. It is designed with
both an oucpur voltage metering
system and a controlled oiitpirt im-
pedance. In these respects, the in-
strument resembles a signal genera-
tor.
The 650 A generates a maxim urn
of 3 volts across a 600-ohm load. The
internal impedance of the unit is
600 ohms so that a maximum of 6
volts is available across high- imped-
ance loads. The output voltage is
controlled by a 600-ohm attenuator
whose input is monitored by a volt*
meter calibrated on the basis of a
600-ohm load. The attenuator has a
range of 50 db in 10 db steps. A con-
tinuously-variable control is pro-
vided for selecting voltages lying
within the 10 db inter%als- With this
arrangement, voltages from 3 volts
to 3 millivolts can be obtained across
a 600-ohm load. The output voltage
can be further extended downward
with a special ouiput cable provided
with the instrument. This cable has
a buik-in resistive netw^ork that di-
vides both the output voltage and
the output impedance by a factor of
100* Use of the cable reduces the
minimum-available voltage across
600 ohms to 30 microvolts and re-
duces the effective output imped-
ance to 6 ohms.
As a basic laboratory tool, the
65 OA is popular because of its high
degree of flexibility* It can be iised
to test r-f, video, ultra- sonic, and
aud io eq u i p men t.
HIGH-FREQUENCY OSCILLATORS
The Model 650 A, just described,
and the Mm! el 200C, described ear-
lien are included in the high-fre-
quency as w^ell as the general-pur-
pose group because of their high-
frequency ratings of 10 megacycles
^nd 200 kc respectively. A third
high* frequency oscillator is the
Model 200 H, w^hich operates from
60 cps to 600 kc and provides a maxi-
mum of 1 volt across loads of 100 or
more ohms. The internal impedance
of the unit is low^ approximately 100
ohms, to permit use with a -wide
range of load impedances*
The -bp' series includes a number
of other high-frequency oscillators.
These are largely special- purpose
types and are described among the
carrier test group*
lOW-FREQUEMCr OSCILLATORS
The low^est- frequency -hp* oscih
lator is the Model 203 A. Its nominal
low-frequency limit is 0.01 cps, al-
though dial overlap is such that a
typical instrument is calibrated and
operates down to less than 0.008 cps*
The upper frequency limit is 1000
cps* The 202A is termed a 'Tow^ Fre*
quency Function Generator" and
generates sinusoidal, square, and
triangular output waveforms at an
amplitude of 30 volts peak-to-peak
across loads of lOOf) or more ohms.
The circuit design of the 202A is
such that transient conditions
caused by range switching or fre-
quency changing is virtually non-
existent, a great convenience in low-
frequency w^ork w^here much time
can be required for circuits to stabi-
liie. Another feature of special value
is chat the instrument supplies a
trigger pulse for synchronizing ex-
ternal equipment.
Principal applications for the
202A include geophysical and medi-
cal work, and studies of ser\o and
other low-frequency^ electrical and
mechanical ^Viiems*
Fig* 2* -hp- Model 204 A hatu^ryo Iterated
oscillator. Splasb-pvfiof case jttcilitntei
field use.
The next lowest- frequency -/j/?-
oscillator is the Model 202B, which
operates from I cps to 50 kc. The
output of the instrument is sinusoi-
dal with a maximum output of 10
volts across a load of 1000 or more
ohms. Applications for this instru-
ment are similar to those for the
202A.
The third low- frequency oscilla-
tor^ the Model 204A, is a battery-
operated type instrument that has
been designed for field use. The os*
ciUator is housed in a splash- proof
case, is light in w^eight (24 lbs.), and
is otherwise easily portable. It oper-
ates at frequencies dow^n to 2 cps
and up to 20 kc and provides a maxi-
mum output of S volts across loads
of 10,000 or more ohms*
The remaining tw^o instruments
In the low-f requeue)' group are the
Models 202D and 200D* The 200D
w^as included as part of the general-
purpose group hut is listed in the
low-frequency^ group because of its
low^er frequenc)' limit of 7 cps*
The Model 202 D operates over a
range from 2 cps to "^0 kc, providing
10 volts across loads of lOOO or more
ohms* The lowest frequency range
of the 202D extends from 2 to 50 cps.
)Copr. 1949-1998 Hewlett-Packard Co.
providing a broad, uninierrupted
low- frequency sweep suitable for
resting low-frequency devices,
BATTERY-OPERATED
The usefulness of a portable, bat-
ter) -operated oscillacor is not con-
ilned to field applications. For ex*
ample, a portable oscillator is useful
where tests must be made in various
parts of the factory where power
outlets are not available. Also, a bat-
tery-operated oscillator is valuable
in the laboratory when a hum-free
signal is required.
► The portable Model 204 A battery--
operated oscillator, described in the
low-frequency group, operates from
2 cps CO 20 kc. The instrument is
used in a wide variety of applications
requiring a strictly self-contained
instrument.
EXTRA-LOW DISTORTION
in audio work there are a number
of applications that require a test
voltage having unusually low dis-
tortion. Although the R-C oscillator
is inherently a low-distortion type
generator with usually less than 1%
distortion, one of the -bp- oscillators
is designed to have less than 0.5^
distortion'^ at power levels up to 1
watt. This osciHator is the Model
20 IB which operates over a range
from 20 cps to 20 kc and has a maxi-
mum output of 3wattsinto600ohms.
At the 3- watt output level, the dis-
tortion is less than 1%.
The output impedance of the
Model 20 IB is 600 ohms, except at
full output, permitting measure-
ments on audio lines. How^ever, the
output system is single-ended. A
T-pad is used to control the output
power, providing a fixed signal-to-
noise ratio, A conventional ampli-
tude control is also provided to limit
the driving level for the output am-
plifier when the extra- low distortion
output IS desired.
HIGH-RESOLUTION OSCILLATOR
In frequency measurement work
there is often a need for an oscillator
^Fiic u$e in hi|;hcsr quality applicitiDiisf. ihc
-hp- MfiJel ZiJfiA Audif} Si;?nal Cient^niEor. not
Fig. 3. Dhit me^ on -hp- Model 2001
Spread-sfule oaciUaior.
having high dial resolution. The
principal requirements for such an
instrument are that the dial have a
large number of calibrated points*
that the calibration be accurate, that
the instrument operate down to low
frequencies of a few cycles per sec-
ond, and that a generous output volt-
age be provided.
Such an instrument is the -bp-
Modet 2001 Spread-Scale Oscillator-
It operates from 6 cps up to 6 kc,
covering this range in six bands.
The frequency control dial is a large
six-inch diameter disc with tu^o
range calibrations. One range has
approximately 160 calibrated points,
while the second has approximately
1 10, giving a total of approximately
270 calibrated points for the band
from 6 cps to 60 cps.
The 2001 is specified to be accu-
rate within 29f» However, screw*
driver adjustments are provided for
standardizing the calibration against
a known frequenc>\ After standard*
izing, the calibration is accurate
within V(. Dial resolution and me-
chanical quality of the tuning sys-
tem are such as to give the 2001 a
resetability well within iCf.
Maximum output from the 2001 is
10 volts across loads of 1000 or more
ohms, A conventional amplitude
control adjusts the output.
CARRIER TEST OSCILLATORS
Five of the -bp- oscillators are
widely used in testing carrier-com-
munications equipment. The most
versatile of these is the -hp- Model
233 A. This instrument has many
features that make it suitable for
testing and adjusting the most ad*
vanced types of carrier equipment.
©Copr. 1949-1998 Hewlett-Packard Co.
The Model 233A operates from
50 cps to 500 kc and provides a maxi-
mum output of 3 watts into a 600-
ohm load at frequencies above 5 kc.
The output system is balanced, per'
mitting operation directly into bal-
anced lines.
In addition to the 3-watt output
system which is designed for use at
frequencies above 5 kc, the 233 A has
a second set of output terminals.
This system issingle*endc-d and is de-
signed to permit testing at frequen-
cies lower than 5 kc. The single-
ended output system provides a max-
imum of approximately 6 volts
across a 600-ohm load. The internal
impetlance of the low-frequency out-
put IS approximately 6 ohms, thus
providing a constant* voltage type
test signal.
The versatility of the 2 33 A is fur-
ther increased by the use of an inter*
nal modulator. This circuit allows
the generated frequent^ to be mod-
ulated by a standard telephone set,
permitting voice communication be-
tween the test point and the termi-
nal. A patiel jack is provided on the
oscillator for connecting the micro-
phone.
The maximum power of 3 watts
available from the balanced ovitput
is usually sufficient to test lines more
than one hundred miles long- To ob-
tain this power economically, the in-
ternal impedance of the 3-watt sys-
tem has been kept moderately low.
However, the system is balanced and
a generator impedance of 600 ohms
can easily be obtained by inserting
suitable resistors in series %vith each
generator terminaL The %'oltage
• ^
^
Fis;, 4. -hp- Model 2^} A Carrier Test Oj-
L ill at or operates from 50 ips to 500 kc*
Operating feal^res tHcltdde balanced,
metered autptit and high resolutsan diaL
across the terminals is monitored by
a volt merer calibrated both in volt-
age and in dbm referred to a 600*
ohm level. Other features of the
2 33 A include a large 9* inch tuning
dial that gives high resolution and a
convenient arrangement for stand-
ardizing calibration, when desired.
A second high-power t^'pe carrier
test oscillator is the -hp- Model 232 A.
This instrument is somewhat similar
to the M(xlei 233 A, but provides
even more powder— 5 w^atts into 500
ohms— and operates over a somewhat
different frequency ratige— 20 cps to
200 kc. A modulator is also included
so that voice communication can be
used to aid in testing.
LOW FOWER CARRIER OSCILLATORS
Three of the -bp- carrier test os-
cillators are lou^-povia^r instruments.
Of these, tw^o have balanced output
circuits and one is single-ended.
The single-ended instrument is the
Model 200H, described earlier with
the high-frequency group. The
20011 operates from 60 cps to 600 kc
and provides a maximum output of
1 volt across 100 or more ohms.
One of the balanced output instru-
ments is the Model 2 30 A, which op-
erates from 35 cps to 35 kc. Maxi-
mum output from the instrument is
+ 14 dbm (approximately i volts)
into a 600-ohm load. The internal
impedance is also 600 ohms. An ar-
rangement for standardizing the fre-
quency calibration is included to
give \% dial accuracy' after stand*
ardization.
The t [i i rd I o w - po we r ca rr ier osc i 1 -
lator is the Model 231 A, which has a
balanced output and operates from
7 cps to 70 kc. The 231 A is provided
with both a 600-ohm and a low^-im-
pedance output system. The 600-
ohm system Is brought out to a parr
of telephone jacks at a maximum
output level of +14 dbm. The 600-
ohm system is balanced and can be
used at frequeticies dow^n to 100 cps.
The low- imped a nee system is single-
ended and provides a maximum out-
put of 10 volts across J 000 or more
ohms. This output can be used down
to 7 cps for testing relays, etc.
AUOtO MATCHING TRANSFORMER
Manv 4 if the -hp- audio oscillators
are provided with a single- ended
type output system in which one of
the output terminals is grounded.
To permit such oscillators to be
used w^ i t h ba 1 a n ced sy s te m s, a s pec i a 1
balanced imi versa 1 matching trans-
former is available as a separate 'hp-
accessory. This transformer, the -bp-
9 1 2- 1 7» is in every way a high-qualit)'
device, having low distort ion, a w^ide
frequency range, lynd good balance.
The measured distortion charac-
teristic for a representative 912-17
transformer is shown in Fig. 5. The
'hp- TEST OSCILLATORS
□9-
31
a tJJ
— ,
- ^
Fig. 5* lypical tiiilfjrtton characteristic tif
'hp- 912-17 Unitersai Matching Tr arts-
far mer operated at -\-l5 dhfn.
transformer is specified to have less
than \% distortion at 20 cps, al-
though cypically the distortion is
substantially less than this figure.
The rated frequency range is from
20 cps to 20 kc, and the response is
within ±\ dh over this range. Maxi-
mum rated power level is + 15 dbm
{4 A volts across 600 ohms).
The transformer is arranged to
match 600 ohms to impedances of
600, 250, 150, 62.5, or 37,5 ohms.
Impedances of 500 ohms can be
matched to 500, 208, 125. 52, or 32
ohms. Complete application data is
supplied with each unit.
fl&on
P»f>CtL
fOOC ** —
mr\ \ 1
m
fig* 6. Typical set- ftp using -hp- 912-17
transformer to match sittgle-ended oscri*
lator to balanced system.
-hp-
MOOIL
20oa_
200C
200D
7{xm
SOOI
2ttTB
2Q2A
202D
WAA
mnA
^1A
232A
233A
650A
FREQUENCr
RANGE _
35 cpv 3S kc_^
20 cps-20 kc
PRINCIPAL
APPLICATIONS
Audio tuili
Audio tifrsK
MAXIMUM
OUTPUT
72-5 V qici'os^ 500 Of more ohms
NOTES
20 cps -200 Itc
7 Gps-70 U
Aud^ci and utifosonic ici*s,
Audio ond uhrasonic t^sls
23,5 w tytiToa^ 50Q or more ohms
10 V ucross 1000 or more ohms
9 D V across 1000 or mor« ifhtns
60 cps-600 kc
Corri&r, f^lepKona tests
Jnferpololion, Frequency
meoSfUrements
10 c|»-20 kc I High fideETtY oudeo tests
I V pcro^s TOO or moreohmi
6 cps'6 kc
10 V ocrass 1000 Of more ohms
42.5 V f3 Vf) cirross AOO or more ohms
high resoEuTion,
spread-scole oscillator
Disrorflon less than 0^%
0.01 cp5-1 kc I Low frequency measuremenls
30 V p-p D>cross \Q00 or mofe ohms
Sme, square, and.
triangular output wave foffns
0,5 CP&-50 kc Low freoruency meas^urements
10 V across TOGO Of more ohms
a cps-70 ke
Low frequsficy measurements
TO y DC r ass 1000 o? more ohmi
2 cps- 20 kc
Low frequency, audio tcsti
in field ond foctory
5 V acrois 10,000 or frtore ohms
as cps- 35 kc
7 cps-70 ke
20c|»ft-2QQkc
50 cps- 500 kc
10 cps-10 mc
Audio,
carrier communaco*ioni^ -e-^t^
AU d i O r
corf ter communiceiticins tests
4 V across 600 or more ohms
4 V oaoii 600 Of more ohms
SotteTY'Operoled; portable
Salonced, 600-a^m output
PRICE
SI 20 .00
SI 20. 00
S15D.00
SI 75 00
_S350 00 "
S225O0
'laso.oo
S450.00
S350.00^
527500
SI 75.00
S275.00
Solonced 600-ohm oulpyt^
nfso has low Z^ 10- volt output syste
I $210.00
Carrier communtcoTcons,
ultrosoniG tests
CMmuT contmunicntieit^
uttrasonic tests
?12-17 20!;ps-20kc
Audio^ ultrosonFC^
video, r-f tests
Univ«rs«| rnotchins
trnrtrnfoFfner
5 wotts into 500 ohms
Metered output
3 wotts Into 600 ohms
Metered output; balonced
S V across 600 or more ohms
Metered output ond
oufpuJ ol-tenuator
-^T5 dbm moximum input
balanced; motches vofaous I's
to 600 ajid 500 ohms^
S35O.O0
S47J.00
S475.fiQ
£25.00
)Copr. 1949-1998 Hewlett-Packard Co.
