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Full text of "Hewlett-Packard Journal Vol. 3 No. 4 (1951-12)(Hewlett-Packard)"

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y Jb"^ technical information FBOM the -hp- LABORATORIES 

VOL. 3 No. 4 


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 

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 



)Copr. 1949-1998 Hewlett-Packard Co. 





\™ HIGH 


200A 650A 
200B 200C 
200C 200H 

200D (See also 
650A "Carrier TesH 

202 D 


201 B 


2 32 A 

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- 

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. 


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* 


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 

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, 


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 


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. 


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. 


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- 

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. 


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* 

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. 


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 




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. 


fOOC ** — 

mr\ \ 1 


fig* 6. Typical set- ftp using -hp- 912-17 

transformer to match sittgle-ended oscri* 

lator to balanced system. 

















35 cpv 3S kc_^ 
20 cps-20 kc 


Audio tuili 
Audio tifrsK 


72-5 V qici'os^ 500 Of more ohms 


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 
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 


50 cps- 500 kc 

10 cps-10 mc 

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 


SI 20 .00 
SI 20. 00 
SI 75 00 
_S350 00 " 





SI 75.00 


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 


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^ 





)Copr. 1949-1998 Hewlett-Packard Co.