GENERAL RADIO COMPANY 1263-8 User manual

OPERATING INSTRUCTIONS
TYPE 1263-8
AMPLITUDE-REGULATING
POWER SUPPLY
GCN£RAL RADIO COMP A NY
D

OPERATING INSTRUCTIONS
TYPE 1263-B
AMPLITUDE-REGULATING
POWER SUPPLY
Form 1263-0110-D
July, 1962
GENERAL RADIO COMPANY
WEST CONCORD, MASSACHUSETTS, USA

Copyright 1961 by General Radio Company
West Concord, Massachusetts, USA

Figure 1. Panel view of1'ype 1263-IJ Amplitude-Regulating Power Supply.

SPECIFICATIONS
Rf Output Voltage: 0.2 to 2.0 volts behind
50 ohms for any recommended oscillator (see
below), and a Type 874-VR Voltmeter Recti-
fier. With 1-kc square-wave modulation, 0.2
to 1.0 volt behind 50 ohms.
Rf Output Regulation: Below 500 Me, rf out-
put of recommended Unit Oscillators is held
to within ±5% including the effects of har-
monics. This regulation can be attained up
to 2000 Me if proper low-pass rf filters are
used and a correction applied for the output-
rectifier frequency characteristic.
Modulation
Frequency: 1-kc square-wave, adjustable
±5%, stable to within 5 cps over the rated
range of line voltage.
Duty Ratio: 0.5 to 0.53, adjustable to com-
pensate for oscillator starting delay.
Rise and Decay Times: 50 f.Lsec each.
Overshoot: None.
Ramp-off: Less than 0.5%.
Gate Voltage: Synchronized with "off" in-
terval of modulation, exceeds 1 volt into the
the
recommended load of 30 k.O shunted by
300 pf. Rise and decay times are less than
50 f.Lsec each. Gate output during "on" in-
terval of modulation is less than .01 volt.
Plate Supply Output: 0 to 300 volts at 30 ma.
Heater-Supply Output: 6 v ±10% at 0.5 amp,
5.4v ±10% at 0.7 amp.
Response Time: For a 2-to-1 step variation
in oscillator output, correction is completed
within 0.5 msec with cw operation, 50 msec
with 1-kc modulation. Recovery time after
blanking is less than 2 msec with cw opera-
tion less than 200 msec with 1-kc square-
wave modulation.
Hum and Noise: Peak residual hum and noise
modulation is less than ±0.3% on cw; less
than ±3% with 1-kc square-wave modulation.
Output Voltmeter: Internal standardizing cir-
cuit is provided. Accuracy after standard-
ization is better than ±10% of indication
when a correction is applied for rectifier
characteristic at extremely high frequencies.
Tube Complement: Four 12AX7, one each
5963, 6V6GT, OA2.
Power Input: 105 to 125 (or 210 to 250). volts,
50 to 60 cps, 55 watts maximum, at full load.
Accessories Supplied: Type CAP-22 Three-
Wire Power Cord, connector cable for modu-
lation jack on oscillator, spare fuses.
Other Accessories Required: Type 874-VR
Voltmeter Rectifier, Type 874-R22 Patch
Cord for connecting output rectifier, and Type
874-T for monitoring oscilloscope connection
in sweeping applications.
Recommended Oscillators: Type 1215·B (50
to 250 Me), Type 1209-BL (180 to 600 Me),
Type 1209-B (250 to 920 Me), Type 1361-A
(450 to 1050 Me), Type 1218-A (900 to 2000
Me), and for cw operation only Type 1211-B
(0.5 to 50 Me).
Other Accessories Available: The Type
1750-A Sweep Drive is recommended for auto-
matic operation. Coaxial Cables, connectors,
attenuato;s, filters, adaptors, and relay-rack
adaptor panels are available.
Mounting: Aluminum panel and cabinet.
Dimensions: Width 8, height 7, depth 9XI
inches (205 by 180 by 235 mm), over-all.
Net Weight: 14~ pounds (6.6 kg).

Section 1
INTRODUCTION
1.1 PURPOSE.
The Type 1263-B Amplitude-Regulating Power Supply (Figure 1) is
designed to operate General Radio Unit Oscillators or oscillators with
similar power requirements. This power supply automatically adjusts
the plate current supplied to an oscillator to maintain the rf output volt-
age at a constant preset level. This constant output is of great advant-
age in frequency-response measurements, :;~nd is particularly important
when the oscillator frequency dial is mechanically swept for use with an
oscilloscope or recorder. The oscillator must have suitable connections
for application of a modulating voltage (as have Genera l Radio Unit Os-
cillators). There must also be available an output rectifier to supply a
negative de potential proportional to the oscillator rf output. In Figure
2, a Type 1263 -B Amplitude-Regulating Power Supply is shown with a
Type 1750-A Sweep Drive, driving a Type 1209-B Unit Oscillator. The
Type 1263-B Amplitude-Regulating Power Supply was designed especially
for use with oscillators driven by the Type 1750-A. It is equally useful
with the Types 907-R and 908-R Dial Drives (see paragraph 1.3.6) and
with manually operated oscillators.
For most swept - frequency applications, cw operation is desirable
because fast regulating action is possible. However, in this instrument,
Figure 2. Type 1263-B
Amplitude-Regulating
Power Supply and
Type 1750-A Sweep
f>rive shown driving a
Type 1209-H Unit
Oscillator.

GENERAL RADIO COMPANY
internal 1-kc off-on modulation is provided for use with a sensitive de-
tector such as an rf demodulating rectifier followed by a 1-kc selective
amplifier.
The Type 1263-B also supplies heater voltage to the oscillator.
Output voltage and current specifications are: plate supply, 0 to 300 volts
at 30 rna; heater supply, 6 volts at 0. 5 amp.
1.2 DESCRIPTION.
1.2. 1 CONTROLS. The following controls are on the Type 1263-B Am-
plitude-Regulating Power Supply:
Name
POWER
ZERO
CAL
OUTPUT
VOLTAGE
ADJ MOD
FREQ
INCREASE
DUTY
RATIO
Description Positions
Two-position POWER, OFF
toggle-switch
with pilot
light
Two-position
toggle-switch
Five-position
selector
switch
Recessed
thumb-set
control
Recessed
thumb-set
control
Continuous
rotary control
Continuous
rotary control
Recessed
thumb-set
control
CW-1 kc rLJ
MOD
ZERO, CHECK
CAL, OPERATE
UN REG
2
Function
Turns power on or off.
Selects cw or 1-kc square-
wave modulation.
Permits output voltmeter to
be checked and calibrated
with output rectifier in use,
without disturbing any con-
nections to oscillator, and
switches off amplitude con-
trol.
Output-voltmeter zero ad-
justment.
Output-voltmeter calibra-
tion adjustment.
Sets output level.
Adjusts modulating fre-
quency over narrow range.
Permits symmetrical square-
wave modulation even with
appreciable starting delay in
oscillator.

TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
1.2.2 CONNECTORS. The following connectors are on the Type 1263-B
Amplitude-Regulating Power Supply:
Name
Description
Function
POWER
Four-terminal Direct plug-in connection for power
socket
cables of General Radio Unit Oscilla-
tors.
MODULATION
Two-terminal
Connection to modulation terminals of
plug oscillator.
For General Radio Unit Os·
cillators, connection is via patch cord
with two-terminal socket on one end and
telephone plug on other end.
OUTPUT
Recessed
Center conductor connects to output
RECTIFIER
Type 874 rectifier, shield connects to output-rec·
Coaxial
tifier ground.
Connector
BLANKING
Telephone- Connection for an external contactor to
tip jacks blank or cut off oscillator output.
Used
(two)
in sweep applications to eliminate re-
turn trace and provide a zero reference
base line on sweep display.
GATE
Phone jack Modulation-gate output for use with syn-
chronous demodulator system.
Three·termi-
Connection for ac power, through de·
nal plug.
tachable line cord.
1.2.3 METER. The OUTPUT VOLTAGE meter indicates theoutput volt-
age, and is the means of checking the regulating action of the power sup-
ply. The meter is an internal de vacuum-tube voltmeter, calibrated in
volts of rf output. The quasilogarithmic scale covers a range from 0 to
2 volts. An internal calibration circuit permits the meter to be standard-
ized with a particular output rectifier. By means of a panel selector
switch, calibration and zero adjustments (thumb-set controls; refer to
paragraph 1.2.1) can be made quickly without disturbing connections to
the oscillator.
1.2.4 FUSES. Line fuses are accessible from the left-hand side of the
instrument. Slow-blow 0.8-ampere fuses are used for 115-volt operation,
and slow-blow 0.4-ampere fuses are used for 230-volt operation.
3

GENERAL RADIO COMPANY
1.3 ASSOCIATED EQUIPMENT.
1.3.1 UNIT OSCILLATOR. The following is a list of recommended Gen-
eral Radio Unit Oscillators:
Type No.
1211-B*
1215-B
1209-BL
1209-B
1361-A
1218-A**
Frequency Range
0.5 to 5 Me; 5 to 50 Me
50 to 250 Me
180 to 600 Me
250 to 920 Me
450 to 1050 Me
900 to 2000 Me
An earlier "A" model of the Type 1211, 1215, or 1209 Unit Oscil-
lator will operate satisfactorily with the Type 1263-B Amplitude-Regu-
lating Power Supply if the telephone plug is removed from the modulation
cable or is adapted to connect to the screw-terminals on the oscillator.
Types 1208-A and -B Unit Oscillators cannot be used with the Type
1263-B Amplitude-Regulating Power Supply. Other oscillators with suit-
able power requirements can be operated from this power supply if a de
connection can be made to the cathode circuit to apply plate-current control.
1.3.2 OUTPUT RECTIFIER. The General RadioType 874-VR Voltmeter
Rectifier is recommended for use as the output rectifier over the frequency
range of 0.5 to 2000 Me. It can be plugged directly into the output con-
nector of General Radio Unit Oscillators, and provides a matched source
for 50-ohm coaxial cable. The backresistance of the crystaldiode should
exceed 40,000 ohms. The ripple in the output of the rectifier must be less
than 10 percent at frequencies above 0. 5 Me to prevent overloading the con-
trol amplifier; this condition is satisfied when a Type 874-VR with a good
crystal diode is used. With the Type 874-VR Voltmeter Rectifier, there-
sponse time is essentially determined by the internal compensation in the
power supply. The stability of the control system (freedom from hunting
and oscillation) is established by this compensation.
1.3.3 OUTPUT FILTER. To minimize errors due to oscillator harmon-
ics, a low-pass filter can be used between the oscillator output and the
output rectifier (refer to Section 5). The following General Radio filters
are recommended:
Type 87 4-F 185
Type 87 4- F 500
Type 874-F1000
Type 874-F2000
• Not recommended for modulated operation •
185-Mc Low-Pass Filter
500-Mc Low-Pass Filter
1000-Mc Low-Pass Filter
2000-Mc Low-Pass Filter
.. For both cw and square-wave modulated operation with the Type 1263-B, set the Type
1218-A selector switch to CW.
4

TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
1.3.4 MATCHED DETECTOR. In setups for measuring transmission or
frequency characteristics of various elements and networks, a Type
874-VQ Voltmeter Detector, terminated in a Type 874-WM Termination
Unit, can be used at the output of the unknown to measure the output
signal. The Type 874-VQ Voltmeter Detector is similar to the Type 874-VR
Voltmeter Rectifier (paragraph 1. 3.2), except that it does not contain a
series 50-ohm resistor and does contain compensating elements to min-
imize discontinuity produced by the shunt reactance of the crystal diode.
A block diagram of the set-up for plotting frequency characteristics of a
Type 874-F185 Low-Pass Filter is shown in Figure 3. In this diagram,
the output of a Type 1215-B Unit Oscillator, regulated by the Type 1263-B
Amplitude-Regulating Power Supply, is fed through the output rectifier
(874-VR) to the device under test (874-F185). The output from the de-
vice under test is detected by the properly terminated Type 874-VQ Volt-
meter Detector and the characteristics are plotted on an x-y plotter.
1.3.5 SWEEP DRIVE. The General Radio Type 1750-A Sweep Drive can
be used with oscillators operating from the power supply to produce a
sweeping frequency source with constant rf output over the sweep range.
This sweep drive also has a blanking voltage and provides a cathode-ray-
oscilloscope deflection voltage synchronized with the position of the
driven dial.
1.3.6 DIAL DRIVE. For permanent, precise recording of data, a two-
axis plotter is an invaluable accessory. The General Radio Types 907-R144
and 908-R96 Dial Drives are designed to sweep equipment using stand-
ard General Radio 4-inch (Type 907-R Drive) and 6-inch (Type 908-R
Drive) dials. The Type 1263-B Amplitude-Regulating Power Supply,
used with any of the oscillators listed in paragraph 1.3.1, will provide a
TYPE
1263-B
AMPLITUDE
REGULATING
POWER SUPPLY "y" AXIS
SIGNAL
!
DEVICE
I
UNDER
TEST
TYPE TYPE TYPE TYPE TYPE
1215-B
r-
874-VR
r-
874 -F185
-
874-VQ
1--
874-WM
XY
UNIT VOLTMETER LOW
PASS
VOLTMETER
5011
PLOTTER
OSCILLATOR RECTIFIER FILTER
DETECTOR TERMINATION
).-
i
TYPE
"X" AXIS SIGNAL
DC
908-R96
-
SUPPLY
DIAL
DRIVE
Figure 3. Typical setup for plotting frequency characteristics.
5

GENERAL RADIO COMPANY
constant output voltage in order that the final recording will be a direct
indication of relative response. In the block diagram of Figure 3, a
Type 908-R96 Dial Drive is shown driving a Type 1215-B Unit Oscillator,
with the detected output of a low-pass filter plotted by an x-y plotter.
1.3.7 SENSITIVE DETECTOR. A Type 874-VQ Voltmeter Detector fol·
lowed by a Type 1232-A Tuned Amplifier and Null Detector tuned to 1 kc
be used for increased detector sensitivity when 1-kc modulation from the
Type 1263-B is applied to the oscillator.
Section 2
THEORY OF
OPERATION
2.1 GENERAL.
In the cw mode of operation, the Type 1263-B Amplitude-Regu-
lating Power Supply compares the de potential developed by the oscil-
lator output rectifier with a de reference potential, and applies a correction
to the oscillator plate supply to minimize the difference. The load re-
sistance presented to the output rectifier is 100,000 ohms. A maximum
of 300
volts at 30 milliamperes is available for the oscillator plate. The
de reference potential is adjustable from 0 to 2.5 volts, which corre-
sponds to an rf output of 0 to 2 volts with the normal output rectifier.
This power supply will maintain any preset level within 2 percent over
the frequency range (subject to additional variations due to harmonics
and possible errors of the output rectifier), provided that the oscillator
produces at least 2 volts with a 300-volt, 30-milliampere plate supply
at all frequencies within its range.
-In the 1-kc modulated mode of operation, the regulating action is
maintained and the carrier, or average rf, level is controlled. This level
is one-half the "on" level of the rf-modulated output. Carrier output is
limited to 1 volt with the recommended oscillators.
6

TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
2.2 CIRCUIT.
The elementary schematic diagram (Figure 4) illustrates the prin-
ciples of operation's of the power supply. The output rectifier develops
a negative de potential proportional to the rf amplitude at the oscillator
output. This potential is applied to the voltmeter amplifier and to one
grid of the first difference amplifier. An adjustable negative reference
potential is applied to the other grid of the first difference amplifier. An
increase in the negative potential developed by the output rectifier, with
respect to the reference potential, is amplified by the two difference am·
plifiers, and appears as an increased negative potential at the output·
amplifier grid. This reduces the plate current supplied to the oscillator.
Conversely, a decrease in output produces an increase in plate current
applied. This closed-circuit feedback system holds the output close to
a preset level. An external contactor shorts the reference potential to
effect rf blanking.
With internal 1-kc square-wave modulation, the regulating action
described above continues except that an RC filter is switched in to pass
only the average de from the output rectifier, and the plate supply is
interrupted with a 1-kc square wave. Under these conditions, the average
or carrier level of the oscillator output voltage is regulated. Variable
resistors in the 1-kc multivibrator circuit permit adjustment of the fre·
quency and duty ratio of the square-wave modulation over a narrow range.
For cw operation, the multivibrator is biased to the "on" state and mod-
ulation ceases.
Figure 4. EleT(lentary Schematic for
Type 1263-B Amplitude-Regulating
Power Supply.
1 .... ,..,...~ .. ,...
I
I
I
I T
L ________ J
I -250v
I I_ 50v
: 1-150¥
L-----------------------------------------------------------J -2.50v -;_ _ _J~
7

GENERAL RADIO COMPANY
2.3 RESPONSE TIME.
In swept-frequency applications, rapid variation of oscillator out-
put is likely to occur, particularly in the uhf range. This variation can
be nearly eliminated by the Type 1263-B Amplitude-Regulating Power
Supply. Cw operation is recommended for most sweeping applications
since the most rapid regulator response is obtained in this mode. With
cw operation the Type 1263-B will correct a 2-to-1 step of oscillator out·
put voltage in less than 0.5 millisecond. If blanking is applied by shorting
contacts in the sweep-drive mechanism, regulation is restored within 2
milliseconds after blanking is removed. With internal 1-kc square-wave
modulation the response and recovery times of the power supply are in-
creased to about 50 and 200 milliseconds, respectively.
With cw operation the recommended General Radio Unit Oscillators
can be swept through their entire ranges in less than one-half second
with satisfactory regulation. To ensure complete regulation with modu-
lation, the entire ranges of the oscillators should not be swept in less
than 10 seconds, although good regulation can be obtained over most of
the ranges with a sweep time as low as two seconds.
Section 3
INSTALLATION
3.1 CONNECTIONS. (Refer also to Section 1.3.)
3.1.1 POWER AND MODULATION CONNECTIONS. Plug the Unit Os-
cillator power cable into the multipoint connector on the right-hand side
of the power supply. With the patch cord supplied, connect the MODU-
LATION
plug on the power supply to the modulation jack of the Unit Os-
cillator.
CAUTION
Excessive voltage, even if applied for a short time,
can damage crystal diodes. Do not apply ac power to
the power supply until all connectio.ts between oscil-
lator, output rectifier, and power supply have been
made. When using the Type 1211-B Vnit Oscillator.
tum the selector switch on the power supply to ZERO
while changing frequency range.
8

TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
3.1.2 OUTPUT-RECTIFIER CONNECTION. With a Type874-R22 Patch
Cord, connect the OUTPUT RECTIFIER connector of the Type 1263-B
to the de output (side connector) of the Type 874-VR Voltmeter Rectifier.
The Type 874-VR should be connected as close as possible to the
output connector of the oscillator, either by direct plug-in or with an
output filter interposed (refer to Section 5). The resistor end marked R
should face the load to provide a matched source for a 50-ohm coaxial
line. A Type 874-EL 90 ° Ell and Type 874-Z Stand are useful acces-
sories for connecting and supporting the output filter and Type 874-VR.
Adaptors are available for connectors other than Type 874. Refer to the
table of Type 874 Accessories at the rear of this manual.
3.2 HEATER-SUPPLY VOLTAGE ADJUSTMENT.
There is a considerable variation in the heater-current require-
ments of the various Unit Oscillators. A compromise in voltage supplied
permits satisfactory operation without adjustment. Output is 6 volts at
0.5 ampere with the nominal line-supply voltage. Heater-current require-
ments for oscillators are met as follows:
a. Types 1209-BL, 1209-B, and 1215-B: 6.3 volts at 0.3 to 0.4 am-
pere.
b. Type 1211-B: 5.4 volts at 0.7 ampere satisfactory (nominal re-
quirement is 6 volts at 0.75 ampere).
c. Type 1218-A: has internal heater rectifier. Polarity of de sup-
plied by Type 1263-B Power Supply is chosen so that this rectifier con-
ducts. Oscillator current requirement is less than 0.2 ampere. The drop
in the rectifier and associated filter is such that proper voltage is sup-
plied to the tube.
d. Type 1361-A: 7 volts at 135 rna. Voltage drop within the oscil-
lator reduces the voltage at the tube to 6.7 volts, which is satisfactory
for normal use. If the Type 1263-B Power Supply is to be used only with
the Type 1361-A Oscillator, remove the jumper as described below.
e. Oscillators requiring less than 0.2 ampere at 6.3 volts: Remove
the jumper that connects the terminals of the electrolytic capacitor at
the top center of the Type 1263-B. This jumper is accessible from the
rear after the dust cover and V2 are removed.
9

GENERAL RADIO COMPANY
Section 4
OPERATING PROCEDUR1E
4.1 INITIAL ADJUSTMENT.
After the proper connections have been made to the oscillator and
the output rectifier (refer to paragraphs 1.3 and 3.1), apply power, allow
at least a 2-minute warm up, and check operation as follows:
a. Standardize the output voltmeter.
(1) With the selector switch in the ZERO position, turn the ZERO
thumb-set control to zero the meter.
(2) Turn the selector switch to CHECK and observe the meter in-
dication.
(3) Turn the selector switch to CAL and turn the CAL thumb con-
trol to produce the same indication as noted in (2).
b. Turn the selector switch to OPERATE.
c. Select CW or 1-KC ru MOD.
d. Set the OUTPUT VOLTAGE control so that the desired operating
voltage is indicated on the meter. If it is impossible to reach this level
by advancing the OUTPUT VOLTAGE control, the oscillator cannot sup-
ply this output. As the normal oscillator output coupling is reduced, the
drop-out point of the regulator will occur abruptly, with no noticeable
change in level down to this point, if the system is operating properly.
If, with normal plate supply, the output from the oscillator is much
greater than desired, the control system may become unstable and break
into oscillation. This condition can easily be observed by the action of
the output meter as the oscillator output coupling is varied. As the
coupling (control or loop on the oscillator itself) is increased from the
minimum setting, the indicated voltage should rise to the desired output
level, then remain constant over a part of the range of the oscillator out-
put coupling. Then, if the coupling can be advanced far enough, the
meter will suddenly jump up or down, indicating the unstable oscillating
condition. All General Radio Unit Oscillators are equipped with an ad-
justable output coupling system, so that the above tests can be made.
Once the adjustments have been made, it should be possible to turn the
oscillator dial through the entire frequency range with no noticeable fluc-
tuation in output voltage.
10

TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
4.2 SWEEP APPLICATIONS.
If the oscilfator is mechanically swept for automatic frequency re-
sponse displays, the dynamic regulation of the output should be checked.
A cathode-ray oscilloscope used to present the response is an excellent
means of checking the operation of the power supply and of observing
when optimum output-coupling setting is obtained. When the Type 1750-A
Sweep Drive is used, connect the blanking cable to the BLANKING tele-
phone-tip jacks on the Type 1263-B Amplitude-Regulating Power Supply
to provide a zero-reference base line for the desired response display
and for the checking display. The horizontal input to the oscilloscope
should be supplied with the oscilloscope sweep voltage provided by the
sweep drive. Temporarily insert a Type 874-T in the cable to the out-
put rectifier and connect the vertical input of the oscilloscope to the
connector thus made available. The oscilloscope should be set for de
response. Such changes in connection can be made without turning the
power supply off, provided that the selector switch is set to ZERO. Re-
turn the selector switch to OPERATE. Drive the oscillator over the de-
sired level. Adjust oscilloscope sensitivity to give a suitable horizontal
and vertical deflection. For cw operation, the pattern should be approx-
imately rectangular, with the horizontal portions straight lines. The neg-
ative voltage horizontal portion represents the oscillator output char-
acteristic, and the positive portion the zero level.
With 1-kc internal modulation a similar pattern is obtained except
that the horizontal portions are traced out by two bright spots connected
by a vertical line. The flatness of the path traced by the lower spot is
the indication of flatness of the oscillator output. Since the average
value of the modulated output is regulated, variation in starting delay in
the oscillator over its frequency range will cause variations in the duty
ratio of the square wave and consequently show a variation from flatness.
The use of a matched termination or resistance pad following the output
rectifier will minimize variation of oscillator starting delay.
If the oscillator output characteristic is not shown as a horizontal
straight line, adjust the oscillator output coupling, and, if necessary, re·
duce sweep speed. A broadening or burst of high-frequency voltage on
this line indicates control-system oscillation; to eliminate this, reduce
the output coupling. For best regulation, some readjustment of the os-
cillator output coupling is necessary with changes in the setting of the
OUTPUT VOLT AGE control, particularly with internal 1-kc modulation.
Sharp discontinuities in the output characteristic of the oscillator,
particularly when wide frequency ranges are swept, may require a reduction
in sweep speed so that the control-system response time will permit com-
plete correction of output voltage. With General Radio Unit Oscillators
11

GENERAL RADIO COMPANY
and cw operation this reduction will not exceed the low-speed limit im-
posed by mechanical standards.
Once a flat horizontal line representing the oscillator output-volt-
age characteristic is obtained, the oscilloscope vertical input can be
transferred to the device under test with the assurance that the output
voltage is being regulated by the Type 1263-B.
4.3 INTERNAL AMPLITUDE MODULATION.
In addition to the toggle switch that selects either CW or 1-KC nJ
MOD, there are two controls for internal modulation. If a 1-kc fixed-fre-
quency selective audio amplifier is used with a demodulating detector,
adjust the modulating frequency for maximum response with the ADJ MOD
FREQ control. For a symmetrical modulation. waveform, monitor the de-
modulated output on an oscilloscope and adjust the duty ratio with the
INCREASE DUTY RATIO thumb-set control on the left-hand side of the
Type 1263-B. If a gate voltage is desired for keying a synchronous de-
modulator or for other synchronizing purposes, connect to the GATE out-
put with a standard telephone plug.
4.4 EXTERNAL AMPLITUDE MODULATION.
Although the Type 1263-B Amplitude-Regulating Power Supply was
designed to operate oscillators with cw or internal1-kc square-wave mod-
ulated output only, a limited amount of amplitude-modulating voltage may
be applied to the BLANKING terminals when the Type 1263-B is set for
cw. Connect a blocking capacitor in series with the lead to the high
(red) BLANKING terminal, and set the output voltage to 1 volt. At a 1-
volt output, the input impedance is about 5000 ohms, and a 20-pJ blocking
capacitor is suitable at frequencies above 20 cps. If the blocking capac-
itor is an electrolytic, connect its negative terminal to the high (red)
BLANKING terminal. At outputs smaller than 1 volt, the voltmeter diode
nonlinearity causes greater modulation nonlinearity and lower input im-
pedance. Therefore, it is recommended that if lower outputs are desired,
the required attenua~ion be added at the output of the Type 874-VR.
Figure 5 shows the limit of the resulting modulation as a function
of frequency. This is not a curve of over-all frequency response, but
rather a curve representing the response-speed limitation of the Type
1263-B. Owing to the large amount of feedback in the system, the fre-
quency response is flat below the overload points represented by the
curve. To determine the maximum voltage that can safely be applied at
any frequency, slowly increase the modulating voltage while observing
the output-voltage meter on the Type 1263-B. Set the modulation voltage
just below the point where the meter starts to drop, since this voltage
12

TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
RELATIVE
AMPLITUDE
MODULATION
0 db=
100% A.M.
-10
-20
-30
I
IMPEDANCE AT BLANKING
TERMINALS • 5000 ohms
AT I VOLT R-F LEVEL
{DIRECTLY PROPORTIONAL
1-.
~AM
ITI ~ LEVELl
.;;;;;;::::
NOTES:
~ CURVE REPRESENTS OVERLOAD
I'.
30%A.M.
LIMITATION, NOT FREQUENCY
~--~-- CHARACTERISTIC OF RESPONSE.
RESPONSE IS FLAT FOR All
~ ~~2~LCI~~~s v~~::EES~N;~~S BY CURVE.
~%A.M.
FOR R-F OUTPUT LEVELS LESS THAN
I VOLT THE LIMITING MODULATION
.............. !--
VOLTAGES ARE PROPORTIONALLY SMALLER.
~ I VOLT R-F OUTPUT SHOULD NOT BE
EXCEEDED UNDER MODULATION OR
OTHiR LliiTAIIOis
1
ii!Lr iPPEAR. 1 I
10 100 1000
MODULATING FREQUENCY IN CYCLES PER SECOND
MAXIMUM
pERMISSIBLE
MODULATING
VOLTAGE
O.Bv
0.4v
0.2v
O.lv
0.051/
0.02511
ACROSS
BLANKING
TERMINAL
WITH I VOLT
R-F LEVEL
10,000
Figure 5. Typical external amplitude-modulation characteristics
of the Type 1263-B
produces the maximum modulation that can be obtained without spoiling
the output regulation. Connect a blocking capacitor in series with the
lead to the high (red) BLANKING terminal, and set the output voltage to
1 volt. At a 1-volt output, the input impedance is about 5000 ohms, and
a 20- f.1 f blocking capacitor is suitable at frequencies above 20 cps. If
the blocking capacitor is an electrolytic, connect its negative terminal
to the high (red) BLANKING terminal. At outputs smaller than 1 volt,
the voltmeter diode nonlinearity causes greater modulation nonlinearity
and lower input impedance. Therefore, it is recommended that if lower
outputs are desired, the required attenuation be added at the output of
the Type 874-VR.
If necessary, equip the modulating source with a voltage divider to
limit the voltage available to about 1 volt, so that the modulating voltage
may more easily be set to the required value.
13

GENERAL RADIO COMPANY
Section 5
OUTPUT
RECTIFIER
ERRORS
5.1 GENERAL.
The ability of the Type 1263-B Amplitude-Regulating Power Supply
to maintain a constant oscillator output necessarily depends on the char-
acteristics of the output rectifier. The power supply maintains within
close limits the rectified de produced by the output rectifier, but oscil-
lator harmonics and frequency characteristics of the rectifier can cause
errors.
5.2 OSCILLATOR HARMONICS.
The Type 874-VR Voltmeter Rectifier operates almost as a peak
detector at the high rf voltages, as do most rf rectifiers covering a wide
frequency range. This means that the rectifier can recognize only the
peak value of the rf waveform and can produce a de output proportional
to it. The amount that the radio-frequency fundamental can vary depends
on the percentage of harmonic voltage in the waveform. "In addition, if
the phase of the harmonic changes with frequency with respect to the
fundamental, the variation can be twice the amplitude of the harmonic,
even if the amount of harmonic does not change.
Unfortunately, this condition often exists in wide-range high-fre-
quency oscillators. If the harmonic frequency approaches the resonant
frequency of the voltmeter rectifier (refer to paragraph 5.3), the error is
magnified.
Above about 300 Me, a low-pass filter should be used between the
oscillator output and the voltmeter rectifier to reduce errors due to har-
monics. The frequency range over which such a filter is effective is
limited to somewhat more than one-half the cutoff frequency up to the
cutoff frequency. Thus, the 500-Mc low-pass filter can be used effec-
tively between 300 and 500 Me, the 1000-Mc low-pass filter between 600
and 1000 Me, and the 2000-Mc low-pass filter between 1200 and 2000 Me.
To cover the gaps between these ranges, other filters with suitable cut-
off frequencies are necessary. Usually there is no need to do anything
below 300 Me, but in the 500-to-600 Me range, harmonics usually become
a problem.
Another way of minimizing the effect of harmonics is to operate
the output rectifier at a very low level where the characteristics approach
square law. The minimum reliable control level is approximately 0.2
14

TYPE 1263-B AMPLITUDE-REGULATING POWER SUPPLY
volt for the Type 1263-B Amplitude-Regulating Power Supply, and al-
though this is above the region usually considered to be square law for
the diode used in the Type 874-VR, quite noticeable reduction in the ef-
fect of harmonics can be obtained at output levels approaching this low
limit. When
the polarity of the response detector at the output of the de-
vice under test is the same as that of the diode in the output rectifier (neg-
ative peak rectifier), some apparent cancellation of the effect of har-
monics can take place. This is true where the phase of the harmonics
of the oscillator with respect to the fundamental has not been appreciably
altered in passing through the device under test. While this is not a
true elimination of the effects of the harmonics (since the device under
test is being measured for transmission of both fundamental and har-
monics by such an arrangement), the resulting display is often a truer
picture of the transmission characteristics than could be obtained with
nonmatching diode polarities. For this reason, the recommended matched
detector, Type 874-VQ, is supplied with a diode of the same type as is
used in the Type 874-VR.
5.3 RECTIFIER FREQUENCY CHARACTERISTICS.
The resonant frequency of the Type 874-VR Voltmeter Rectifier is
about 5400 Me. The actual output voltage ,is down from the indicated or
regulated level about 3 percent at 1000 Me and 13 percent at 2000 Me.
Figure 6 illustrates the frequency characteristics of the Type 874-VR
Voltmeter Rectifier or Type 874-VQ Voltmeter Detector with a typical
crystal diode. When the Type 874-VQ Voltmeter Detector is used as the
response detector, there is no need to apply a correction for frequency
response, since the errors in the Types 874-VR and 874-VQ cancel.
1.0
U)
<ll!J
!J 0 .9
0>
> 0
.J 1&.1 . 8
~~
~ ~ ·1
~0
~
.6
r--
·5
0
RESONANT
-
----
i
----
--
...........
FREQUENCY 540C Me.
............
-
r- ....
...
2 3
FREQUENCY- kMc
Figure 6. Resonance correction factors; Type 874- VR Voltmeter Rectifier.
15