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Oct. 22, 1946.‘
2,409,845
P. c. GARDINER ET AL
CALIBRATING DEVICE
Filed Nov. ‘24, 1941
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CALIBRATION ADJUSTMENT
Inventors:
Gaul C. Gar diner”
John E. Maynard;
b.
‘YT?
Patented Oct. 22, 1946
2,409,845
UNITED STATES PATENT orrlcs
2,409,845
CALIBRATIN G DEVICE
Paul C. Gardiner, Scotia, and John E. Maynard,
Schenectady, N. Y., assignors to General Elec
tric Company, a corporation of New York
Application November 24, 1941, Serial No. 420,230
3 Claims.
1
(01. 250-20)
2
Our invention relates to a calibrating device,
radio waves, variably tuned radio frequency cir
and more particularly to such a. device for cali
cuits l I, a radio frequency ampli?er device l2, a
brating variably tuned apparatus.
frequency converter ‘and intermediate frequency
variably tuned ampli?er and oscillator circuits
operating at ultra high frequencies, for example,
ampli?er l3, a second detector and audio ampli
?er l4, an audio power ampli?er device [5, and a
loud speaker [5 through which audio signals are
of the order of 50 to 500 megacycles, are subject
to frequency drift which is generally large with
respect to the frequency band Width necessary to
translated. In operation, the radio frequency cir
cuits are variably tuned through the agency of
translate an ultra high frequency wave through
such circuits. It is, accordingly, desirable to 10
tune such circuits more broadly than is necessary
to accommodate the frequency band width of.
such ultra high frequency waves, so that the effect
of such drift is minimized. For example, in ultra
a control knob ll, which is arranged to change
the frequency to which the radio frequency cir
cuits are tuned and the frequency to which the
converter I3 is tuned simultaneously by equal in
high frequency radio receivers, the receiving cir
cuit may be capable of responding to an ultra
high frequency wave anywhere within a band of
frequencies much wider than the highest trans
mitted audio frequency. When thus lbroadly
tuned, the local oscillator in a superheterodyne
receiver may drift in frequency by substantial
amounts without causing the intermediate fre
quency to change to a region outside of the inter
mediate frequency pass band.
It is desirable that such circuits should be so
calibrated that, before drift occurs, the frequency
of the translated wave is centered in the pass
band of the circuit when they are nominally ad
justed to respond to the waves. It is accordingly
an object of our invention to provide a new and
improved method and means for calibrating such
wide band pass circuits in such fashion.
The response of such wide band pass circuits
is usually more or less non-uniform over the pass
band, and is generally a maximum at some point
in the pass band substantially removed from its
center. It is, therefore, a further object of our
invention to provide a new and improved method
and means for calibrating such wide band pass
crements, so that Waves from the antenna [0 are
selected as desired by the radio frequency cir
15 cuits I I, ampli?ed to the radio frequency ampli
fier device i2, and converted in frequency to the
intermediate frequency by the frequency con
verter I 3.
The ampli?er device 12 has ?Ve electrodes, of
20 which the cathode I8 is connected through a re
sistance I!) ,to ground, and the anode 20 is con
nected serially through a load resistanceil and
an anode current meter 22 to the positive termi
nal of a source of potential 23, whose negative ter
minal is connected to ground. The screen grid
electrode 25 is connected through a resistance 26
to a point between the load resistance ‘2| and
anode current meter 22, which point is bypassed
to ground through a bypassing condenser 21. The
30 suppressor electrode 28 is connected through a
resistance 29 to ground. Waves selected by the
radio frequency circuit from the Waves appearing
on the antenna I 0 are ampli?ed by the device l2
and appear across the load resistance 2|, from
35 which they are impressed on the frequency con
verter and intermediate frequency ampli?er l3
through a coupling condenser 30.
Because the radio frequency circuit I I and the
local oscillator included in the frequency con
circuits without reliance on their response at a 40 verter l3 are variable in frequency by adjustment
single frequency.
The features of our invention which we believe
of the control knob ll, they are not as stable in
frequency as if the local oscillator in they fre
to be novel are set forth with particularity in the
quency converter I3 were controlled in frequency
appended claims. Our invention itself, both as
by a quartz crystal. Even though the components
to its organization and manner of operation, to 45 of these circuits are made of high quality, selected
gether with further objects and advantages
for their high stability during temperature
thereof may best be understood by reference to
change and the like, frequencyldrift of the order
the following description taken in connection
of a few tenths of one percent of the radio‘ fre
with the accompanying drawing in which Fig. 1
quency received is almost inevitable, and it is
schematically illustrates a radio receiver circuit 60 therefore desirable that the pass band of the radio
embodying my invention, and Figs. 2 and 3
frequency circuit II and the intermediate fre
graphically show certain characteristics of the
quency ampli?er circuit l3 be of su?icient width
embodiment of Fig. 1.
to allow for such frequency drift thereby to min
In Fig. 1 the radio receiver includes an antenna
imize the chance that such drift'shall cause the
10 suitable for picking up ultra high frequency 55 ‘output Of the frequency converter i3 to change
2,409,845
4
3
to a frequency outside the pass band of the in
termediate frequency ampli?er.
lower frequencies, or that the signal may drift to
higher frequencies, and in such case transmis
sion through the receiver’ is affected after only a
slight drift. Calibration of the control knob I1
in dependence on a single standard frequency is
therefore undesirable, and generally does not cen
In Fig. 2 there is illustrated a desirable fre
quency characteristic for the receiver illustrated
in Fig. 1. In this ?gure the carrier frequency is
plotted as albscissa, and the output of the second
ter the pass band 49 about the nominal frequency,
detector I4 is plotted as ordinates. The curve 40
--as illustrated by the vertical line 4| in Fig. 2.
in this ?gure illustrates the relation between car
Certain remaining portions of the receiver are.
rier frequency and the second detector output
for one particular setting of the control knob I1. 10 utilized in the calibration of the control knob I1,
and include the audio power ampli?er I5, a gang
The curve 40 indicates that the receiver of Fig. 1
switch
including switch members 5! through 56,
has a pass bandof about 300 kilocycles. It is de
a tuned circuit 51, a quartz crystal oscillator 58,
sirable that this pass band indicated by the curve
and a tuned recti?er circuit 59. When the re“
40 be centered about the radio frequency for
which the control knob I1 is nominally adjusted.
Such frequency is indicatedpby the vertical line
M in Fig. 2, which substantially bisects the pass
band illustrated by the curve 40.
i
The curve 40 has been illustrated as substan
ceiver' is operating normally the conductor 49 is
connected to the control electrode 24 of device I2
and the control electrode of the electron dis
charge devices in the ampli?er i3 through the
switch member 55. The cathode 69 of the power
tiallyflat topped, as is usual in radio receivers, 20 ampli?er I5 is connected to ground, and its con
the ?at topped characteristics being ordinarily
produced by adjustment of interstage coupling in
trol ‘electrode BI is connected to ground through
a resistance 52, and through a coupling condenser
63 and a switch member 52 to the output of the
the intermediate frequency ampli?er I3. It is
second detector and audio amplifier I4. The
usual that such adjustment should produce a sub
stantially ?at topped curve All which, however, is 25 screen grid electrode 64 of the power ampli?er
I5_ is connected through a resistance 65 to the
not entirely uniform over the pass band. In the
positive terminal of the source 23, and the anode
case illustrated, the central portion 42 is lower
66 of the power ampli?er I5 is connected through
than the remaining part of the pass band, the low
the switch member 5i and through the primary
higher,
frequency
andpart
the ofhigh
the frequency
pass bandpart
43 issomewhat
of the passv
of an output transformer 6'! to the same positive
terminal of the source 23. The loud speaker I6
band 44 provides maximum second detector out
put.
is connected to the secondary of the transformer
'
61.
The switch means including the switch mem
through the medium of a calibration knob 50
which is effective to adjust the radio frequency 35 bers 5! through 56 is provided for the purpose of
changing certain connections in the receiver to
circuit II and the frequency converter I3 in the
provide
for the proper calibration of the control
same manner as the control knob [1, but in much
Calibration of. the receiver is accomplished
smaller amounts.
'
knob I'I. Connections through theswitch mem
bers El, 52 and 56 are as described when the
An automatic volume control circuit is pro
vided .for the receiver through a conductor 49 40 switch means is in its right-hand position, the
radio frequency circuit II being connected to the
connected to a point onthe second detector I4 at
antenna I0 through the switch member 54 in that
which aunidirectional voltage is developed which
position.‘ The switch members 53 and 55 make
varies in magnitude with the received signal in
no connection in their right-hand position.
tensity sufficiently for automatic volume control
purposes, the conductor 49 being connected to 45 When the switch means is moved to its ‘left
hand position to provide for calibration of the
supply such potential to the control electrodes 24
of the device I2 and to the control electrodes of
the ampli?er devices in the intermediate fre
control knob H, the anode 65 of the power am
pli?er I5 is disconnected from the transformer
61 and connected through the switch member 5|
quency ampli?er I3 as a bias, to control the gain ,
thereof. The effect of the automatic volume con ' 50 to one terminal of the tuned circuit 51. The cou
trol voltage on the conductor 49 upon the gain of
the receiver may be observed by- variation in an
ode current of the discharge device I2 as indicated
by the anode current meter 22. When a strong
pling condenser 63 is disconnected from the out
put of the audio ampli?er I4 and is connected
through the switch member 52 to a conductor 68
which is coupled through a coupling condenser 69
signal is received, the negative automatic volume .155 to the other terminal of the tuned circuit 51.
An intermediate tap of the inductance of the
control voltage increases, and the current indi
tuned circuit 51 is connected to the positive ter
cated by the meter 22 decreases correspondingly.
minal of the source 23 so as to provide a path
The radio receiver of Fig. 1 may be calibrated
for operating'current to the anode 66 of the power
by adjusting the calibrating knob 50 to a posi
tion such that the meter 22 reads a minimum, . 60 ampli?er I5. The connections described provide
for the operation of the power ampli?er I5‘ with
while a standard frequency signal is placed on
the tuned circuit 5'! as an oscillator whose output
the antenna l0 and the control knob I1 is set to
appears on the conductor 68.
that standard frequency. However, reference to
When the switch member‘ 53 is in its left-hand
Fig. 2 indicates that the receiver is then so ad
justed that the standard frequency applied to the 5165 position, the conductor 68 is connected to the sup
pressor electrode 28 so that the output of the
antenna It) lies within the pass band illustrated
above described oscillator is impressed on that
by the curve 40 at the point 44. Such adjust
suppressor electrode to modulate any ultra high
ment is satisfactory if drift of the pass band is
frequency wave appearing 'on the control elec
toward higher frequencies, or if the signal drift is
toward lower frequencies, since in either such ='7.0 trode 24. Member 54, in its left-hand position,
connects the radio frequency circuit I I to the out—
case, signal transmission through the receiver is
put of the crystal‘ oscillator 58.‘ Switch member
not affected until the pass band or signal fre
55, in its left-hand position, connects the‘ crystal
quency has changed in frequency by about 300
oscillator 58 to the positive terminal of the source
kilocycles. It is quite possible, however, that the
_ pass band illustrated by the curve 40 may move to "75 2.3 of potential so as to. supply operating current
2,409,845
5
to the crystal oscillator. Member 56, in its left
hand position, disconnects the automatic Volume
6
and tuned circuit 51 must be su?icient to cause
the detector I4 to impress a suf?ciently high volt
age upon conductor 82 to cause the diode 81 to
rectify. By preventing the diode recti?er from
control conductor 49 from the control electrode
of the device I2 and the discharge devices in
the intermediate frequency ampli?er I3, and con
responding to voltages below this predetermined
nects such control electrodes through the switch
minimum level, the effect of extraneous noise
member as and through a resistance 8.0 shunted
voltages and the like on the tuned recti?er is
by a condenser 8! to ground.
minimized.
With such connections made through the
When voltage appears on the conductor 82 in
switch members 5i through “56, the oscillator in» 10 su?icient intensity to cause the diode ill! to rectify,
cluding the power ampli?er I5 and tuned circuit
the recti?ed output voltage appears across the
5'! is adjusted to operate at a frequency which is
resistance to, and is impressed upon the control
half the frequency between points on the curve
electrode 26 of the device I 2 and the control elec
48 of Fig. 2 somewhat removed in either direc
trode of the intermediate frequency ampli?ers I3
tion from the substantially ?at topped portion .15 through a conductor 9| and switch member 56 so
thereof. In the case illustrated in Fig. 2 this fre
as to reduce the gain of the device I 2 and the in
quency should be about 175 kilocycles and should
ermediate frequency ampli?er I3 as the voltage
be adjusted experimentally as will be explained
on the conductor 32 increases. When the gain
hereinafter. The output frequency of the crystal
of these devices is reduced, the anode current
oscillator 58 must be a frequency which is nomi 20 of the device I2, as indicated by the meter 22,
nally marked on the control knob I1, to which
is correspondingly reduced, as when the auto
frequency the control knob ll must be set during
matic volume control voltage 5! is applied to the
all calibration operation. The ultra high fre
control electrodes of these devices and increases.
quency wave from the oscillator 58 is transmitted
With the receiver so arranged and connected,
through the radio frequency circuit I I to the am
accurate calibration of the control knob I‘! is
pli?er device I2, where it is modulated in ampli
possible so that the nominal frequency indicated
tude by the 175 kilocycle wave from the oscillator
by the control knob I‘! is located in the center of
including tuned circuit 5'! and power ampli?er
the pass band. of the receiver. To accomplish this
device I5, such wave being impressed on the sup
calibration with the control knob ll set at a
pressor electrode 25. The output of the ampli?er - nominal frequency equal to the standard fre
device I2 is transmitted through the frequency
quency of the crystal oscillator 55, the calibration
converter and intermediate frequency ampli?er
knob 58 is adjusted and results are obtained as
indicated in Fig. 3. In this ?gure the adjustment
I3 and through the detector It. where the modu
lation of the ultra high frequency wave from the
of the calibration knob oil is plotted as abscissa
crystal oscillator 58 is detected.
~ and the anode current of the device I2, as indi
The output of the detector It appears on the
cated by the meter 22, is plotted as ordinates.
conductor 82, and in the calibrationoperation
The curve lull illustrates the relation between
comprises a 1'75 kilocycle wave corresponding to
these quantities, the portion Iii! showing that the
anode current as indicated by the meter 22 is a
the wave from the conductor {is which modu
maximum when the calibration knob 59 is in one
latee the ultra high frequency wave in the device
extreme position. As the calibration knob is
52. The conductor 82 is connected through a
turned from that extreme position toward the
coupling condenser 83, an inductance 8-43 and a
other extreme position. the anode current of the
resistor 85, all arranged in series, to the un
device I2 decreases very slightly for a time along
grounded terminal of the resistance 80. A by
curve portion IilI, then decreases more rapidly
passing condenser 85 is connected between
along curve portion i 632 to a minimum at point
ground and the point between the inductance 84
Hi3. Further angular rotation of the calibration
and resistance .85. Adjustment of either the con
knob 50 from this minimum
produces an in
denser 85 or the inductance 224 may be utilized to
crease in anode current along curve portion let
make the combination of condenser 83 and in
ductance 84 resonant, in series, at the frequency 50 to a maximum point l @5, and another drop along
curve portion its to a minimum, at a point I01,
of the waves on conductor 68. Whenever the
which second minimum is usually of a different
value from the ?rst minimum at point I03. Fur.
the power ampli?er I5 and tuned circuit 51 is
ther rotation of the calibration knob 59 produces
adjusted, the tuned circuit including the con
denser 83 and inductance 34 must be readjusted 55 a rise in anode current along portion I88 of the
curve I50, and a succeeding gradual rise along the
in correspondence. Voltage appearing across the
portion I99 of the curve I68 to the other extreme
inductance 84 is recti?ed in a diode recti?er 8?
position of the knob 50.
whose anode is connected to a point between the
The point I55 of the curve I00, at which the
condenser 83 and inductance t4 and whose cath
ode is connected through a resistance 88 to 60 anode current is maximum, is the correct setting
of the knob 58. The amount of anode current in
ground and through a second resistance 89 to the
dicated by point I05 and the degree of curvature
positive terminal of the source 23 of potential.
of curve vH30 near point H15 may be adjusted with
A bypassing condenser 90 is connected in shunt
in limits by suitable adjustment of the frequency
to the resistance 88 to bypass alternating cur
rent therearound and to maintain the cathode of 65 of operation of tuned circuit ‘51. It is desirable
that the degree of curvature of curve I ?ll near
the diode 8'! effectively at ground potential for
point I 65 shall be reasonably great to aid in accusuch alternating current.
rate adjustment of calibration knob 50.
Since the cathode of the diode 8'! is maintained
When a radio receiver, or other variably tuned
slightly positive with respect to ground by the
voltage divider including resistance 83 and 89, 70 apparatus, is adjusted in accordance with my in
vention so that the nominal adjustment is exact
which are connected in shunt to the source 23 of
potential, the diode 81 cannot rectify until the
ly at the center of the pass band of the apparatus,
alternating voltage across the inductance 84 is
frequency drift of the apparatus, or of signals
above a certain minimum level. The output of
transmitted therethrough, has a minimum chance
the oscillator including the power ampli?er I5 75 ‘for reducing the signal transmission through the
operating frequency of the oscillator including
2,409,845
apparatus, since the amount of drift possible
without ill result is substantially the same in either
direction. In order to achieve these results, it is
desirable that the modulation component of the
output of detector I4 be measured rather than
the continuous current component corresponding
to carrier wave intensity. In the apparatus illu
brating means may be adjusted to produce a
characteristic amount of said side bands-in the
output of said apparatus when said standard freq
uency is centered in said pass band.
2. In combination, a superheterodyne receiver
adapted to receive a high frequency wave having
side bands within a predetermined frequency
range, said receiver having a pass band substan
tially wider than said range to allow for drift in
strated the modulation component corresponds to
the alternating potential wave from the oscillator
including power ampli?er l5 and tuned circuit 10 frequency of said pass band or of said Wave so as
to maintain reception of said wave during said
£1. It is also desirable that the frequency of this
drift, means for impressing a standard frequency
wave on said receiver and for producing side
' bands associated with said wave and spaced apart
Hi9,‘ when the standard frequency carrier wave 15 by an amount comparable to the pass band of
said receiver, and means for indicating the
carrying the modulation wave is centered in the
modulating wave be so adjusted as to produce a
dip in output corresponding to the slight increase
in anode current at the portion I85 of the curve
pass band of the apparatus. By this arrangement
we have provided an ultra high frequency receiver
which is variably tuned, and which has minimum
amount of said side ‘bands transmitted through
said receiver, whereby said receiver may be cali
1. In combination, apparatusfor translating an
uency range to allow for drift in frequency of said
brated in accordance with the transmission of a
change of drifting so far in frequency as to fail to 20 characteristic amount of said side bands through
said receiver so that said standard frequencywave
respond to a signal to which the control knob ll
is received at the center of said pass band.
7 is nominally tuned.
3. In combination, a superheterodyne receiver
While we have shown and described a particular
having means including a local oscillator for con
embodiment of our invention, it will be obvious to
those skilled in the art that changes and modi? 25 verting the frequency of a received wave to
an intermediate frequency, the frequency of
cations may be made without departing from our
such received wave and the operating fre
invention in its broader aspects, and we, therefore,
quency of said oscillator being subject to
aim in' the appended claims to cover all such
drift in frequency, said received wave hav
changes and modi?cations as fall within the true
spirit and scope of our invention.
30 ing side bands within a predetermined freq
uency range and said receiver having a pass band
What we claim as new and desire to secure by
substantially wider than said predetermined freq
Letters Patent of the United States, is:
ultra high frequency wave having side bands
within a predetermined frequency range, said ap
paratus including a variably tuned circuit, means
for calibrating the variable tuning of said circuit,
said apparatus having a pass band substantially
Wider than said predetermined frequency range to
wave or of the operating frequency of said oscil
35 lator so as to maintain reception of said wave
during such drift, means for impressing a stand
ard frequency wave on said receiver and for pro
ducing side bands associated with said wave and
spaced apart by an amount comparable to the pass
'allow for drift in frequency of said pass band or of 40 band of said receiver, and means for indicating
the amount'of said side bands received by said re
said wave so as to maintain translation of said
ceiver, whereby said receiver may be calibrated in >
Wave during such drift, means for impressing a
accordance with the transmissionof a character
standard frequency wave on said apparatus and
istic amount of said side bands through said re
for producing side bands associated‘with said
wave and spaced apart by an amount comparable 45 ceiver so that said standard frequency wave is
received at the center of said pass band.
to the pass band of said apparatus, and means for
indicating the amount of said side bands trans
PAUL C. GARDINER.
mitted through said apparatus whereby said cali
JOHN E. MAYNARD.
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