Super-Pro SP-600JX-21 User manual

HANDBOOK
OPERATION INSTRUCTIONS
RADIO RECEIVER
MODEL SP-600JX-21
(HAMMARLUND)

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i ........ 1 August 1956
21
........ 1 August 1956
22 ........ 1 August 1956
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Revised 1 August 1956

T.O. 31 12-4-1 01-1
Table of Contents
TABLE OF CONTENTS
Section Page
I DESCRIPTION .......................................................................................... 1
1.1 .
General ...................................... , . ,, . , ........... , .... , ........
1
1.3 . Purpose of Equipment ........................................................ 1
. ..............
1.11 . Description of Equipment .................................... ... , 1
1.26 . Operational Theory .............................................................. 4
1.31 . Capabilities and Limitations ...................................................... 5
1.36 .
Equipment Required for Phone or Slow-speed Telegraph
Reception
................... .. ...... ............. ...............................
6
I1 PREPARATION FOR USE ..................................................................... 7
2.1 . Uncrating .................................................................................. 7
2.3 . Inspection ...................................................................................... 7
2.5 . Replacement of Defective Parts ................................................. 7
2.8 . Setting Up the Receiver ........................................................ 7
2.12 . Installation ............................................................................... 10
.........................................................................................
2-19 . Testing 13
I11 OPERATION ............................................................................................... 14
3.1 . General ................................................................................... 14
3.3 . Description of Controls ....................................... ................ 14
3.22 . Presentations and Readings .................................. ...... ...... 16
............................................ ...............
3.25 . Operating Procedures ... 17
........
................................ . .
.
3.54 De-energizing the Equipment , , ,, , 21
..... .. .........
.........................
.
3-57 Precautions To Be Observed .... ...... , , 21
...................................................................
IV EMERGENCY OPERATION 22
.......................................................................................
4.1 . General 22
...........................................................................
.
4-3 Antenna System 22
........................... ...............
.
4-5 Emergency Tube Replacement .... 22
Revised 1 August 1956

Section I
T.O. 31 R2-4-101-1
Figure I -1. Radio Receiver, Model SP-600-JX-2 1

T.O. 311 12-4-101-1
Section I
Paragraphs 1-1 to 1-15
1-1. GENERAL.
1-2. This handbook contains operation instructions for
Radio Receiver, Model SP-600-JX-21, (figure 1-1)
manufactured by the Hsmmarlund Manufacturing Co.,
Inc., New York
1, N. Y.
1-3. PURPOSE OF EQUIPMENT.
1-4. The radio receiver is designed for enclosed-
station, fixed or mobile use. It is adaptable to shipboard,
airborne, or field applications, and nlay be used in a
two-way operational activity. The radio receiver provides
for the reception of keyed, amplitude-modulated, and
frequency-shift carrier signals. The carrier signal intelli-
gence may be slow-speed (manual) or high-speed
(automatic) telegraph, phone, teletype, facsimile, etc.
For Morse code and teletype operation, use is made of
c-w and single-tone carrier signals. For teletype opera-
tion, two-tone and frequency-shift carrier signals may
also be used.
1-5. To render the signal intelligence audible and/or
recordable, auxiliary components are required. When the
receiver is to be used for the reception of phone or
slow-speed telegraph signals, a headset and/or loud-
speaker are used; in other modes of operation, these
components are used to monitor the signal. To receive
high-speed telegraph signals, a recorder driving unit and
/or a tape ink recorder are required. For frequency-
shift teletype reception, use is made of suitable frequency-
shift converter equipment associated with a teletype-
writer.
1-6. The output of the receiver, for signals other than
phone, may be developed in the form of d-c output to
denote a dot (mark) and no d-c output to denote a dash
(space), the signal intelligence being csntained in the
succession of dots and dashes. Alternately, it may be
developed in the form of a-c output wherein, for the in-
terval of each dot (mark), or for the interval of each
dot (mark) and each dash (space), keyed-tone signals
result. The signal in the form of d-c output is suitable
to operate applicable recording equipment such as a tape
ink recorder, a line relay, or a tone generator. The signal
in the form of a-c output provides the audible output of
the system; or it is used to operate a recorder driving
unit associated with the tape ink recorder, or to provide
input to a suitable frequency-shift converter associated
with a teletypewriter.
1-7. The tone generator keyed output may be used
to provide the signal to the headset and/or loudspeaker
monitor. It may also be fed to a transmission line to pro-
vide the signal at the remote end of the line. The keyed-
tone used is in the voice frequency range, each signal
requiring a frequency band of 170 cycles, and the line
may be used for several such tone signals, as well as for
phone signals.
1-8. The radio receiver provides for continuously vari-
able reception within the frequency range of 0.54 mc to
54.0 mc, and for crystal-controlled fixed-frequency re-
ception within the frequency range of 0.75 mc to 54.0
mc. The receiver uses single heterodyne conversion for
its three lower frequency bands and double heterodyne
conversidn for its three higher bands (above 7.4 mc).
The receiver signal-to-noise ratio and sensitivity charac-
teristics provide for the reception of extremely weak
signals and the receiver is well suited for the reception
of short-wave signals which are inherently subject to
nonselective and selective fading.
1-9. The radio receiver has an internal beat-frequency
oscillator used in heterodyne detection of keyed-carrier
signals to provide audio signal intelligence to the head-
set and/or loudspeaker monitor.
1-10. The radio receiver has a self-contained power sup-
ply designed to operate from a 50-cps to 60-cps, single-
phase a-c source within the voltage range of 90 to 270
volts. The receiver power consumption is 130 watts.
The power transformer primary and secondary are sepa-
rately fused. The 1.6-ampere slow-blow primary fuse,
and the %-ampere high-voltage secondary fuse are con-
tained in cartridge-type fuseholders located on the rear
apron of the receiver.
1-1 1. DESCRIPTION OF EQUIPMENT.
1-12. GENERAL. The radio receiver is a 20-tube radio-
comtnunications type designed for direct mounting in
a standard 19-inch relay rack. It comprises a chassis and
light grey front-panel assembly to which are mounted a
top cover and a bottom plate.
1-13. RECEIVER CONNECTOR USES. With the ex-
ception of the headset "PHONES" jack (20, figure 3-I),
located on the front panel, and the "ANT" input con-
nector (8, figure 2-I), all receiver connectors and termi-
nals are located on the rear apron. The a-c power cable
of the receiver is also located on the rear apron.
1-14. The rereiver input circuit is designed to accommo-
date a balanced doublet or straight-wire antenna. The
input impedance of the receiver is designed to match
a 95-ohm transmission line. Other suitable antenna in-
stallations specifically designed for the desired operating
frequency may also be used. The antenna is connected to
the receiver "ANT" input connector (8, figure 2-1)
with type RG-22/U cable.
1-15. The "IF OUTPUT" connector
(6, figure 2-2)
provides a received signal (usually frequency-shift) at
the receiver i-f output for frequency-shift converter use,
usually as part of a space-diversity receiving system. The
i-f output circuit in the receiver is isolated from the
b-f-o circuits, therefore b-f-o injection voltage is not
available at the "IF OUTPUT" connector.

Section I
Paragraphs 1-16 to 1-23
1-16. The reveiver "AUDIO OUTPUT" terminals (8,
figure 2-2) are suited for a 600-ohm loudspeaker or
transmission line. The receiver a-c signal output (phone,
single-tone telegraph or teletype, or two-tone teletype)
is available at the "AUDIO OUTPUT" terminals. To
render high-speed telegraph and single-tone or two-
tone signals intelligible, the tape ink recorder used for
high-speed telegraph and the teletypewriter used for
teletype reception are associatedwith demodulator equip-
ment connected to the receiver by suitable transmission
line. When a local teletypewriter is used to operate
another teletypewriter remotely or locally connected to
the transmission line, the send teletypewriter relay is
connected to the jumpered "AUDIO OUTPUT" termi-
nals so that the line current on "mark" balances out
between the balanced split output transformer windings
of the receiver, for which the jumpered connection pro-
vides a mid-point tap. This use of the line may be
simultaneous io its other uses.
1-17. The receiver "DIODE OUTPUT" terminals
(2, figure 2-2) and the "AVC" terminals (3)
are used to interconnect two receivers in a space-
diversity receiving system. The "AVC" terminal desig-
nated "G" is grounded for each receiver to a common
ground while that designated
"-" is interconnected
between receivers. This is done to provide common avc
between receivers for space-diversity reception of an
ampiitude-modulated or frequency-shift signal. With
this arrangement, the avc due to the stronger signal re-
ceived on one receiver decreases the weaker signal and
-
the noise output of the other. To provide for space-
diversity reception of phone, the audio output from only
one receiver is used. To do this, the jumpered "DIODE
OUTPUT" terminals are ovened on one receiver and
the
"-" terminal connected to the other receiver, which
provides the output. To provide for space-diversity re-
ception of
cw to a tone keyer (generator) or tape ink
recorder. the receiver interconnections are as outlined
for phone, but no avc and no bfo are used. This is the
case when the d-c output from the three interconnected
"DIODE OUTPUT" terminals is used. When the a-c
output is used, the diversity demodulator, associated
with the tape ink recorder, is provided with the a-c
output from the "AUDIO OUTPUT" terminals
(8) of
each receiver. To provide for the space-diversity recep-
tion of frequency-shift carrier signals, the i-f output
or the audio output from each receiver may be used to
provide input to.suitablefrequency-shiftconverter equip-
ment.
1-18. The "AC" power receptacle (12, figure 2-2) on
the rear apron of the receiver may be used for operating
an accessory, such as an electric clock or lamp. Power is
available at the receptacle whenever the receiver is con-
nected to a power source, regardless of the settings of the
receiver controls.
1-19. RECEIVER OPERATION. All operational ac-
tivities require that the receiver switches and controls be
set properly for the mode of operation contemplated.
These controls are all located on the front panel of the
receiver, with the exception of the "METER ADJ RF"
control
(5, figure 2-2) and the "METER ADJ AF"
control
(7) used to calibrate the tuning meter (I, figure
3-1) on the front panel, and the "BFO INJ" adjustment
control (4, figure 2-2), all three of which are located
on the rear apron of the receiver. These controls are
factory adjusted, and are not to be moved from their
adjustment positions.
__
1-20. Theradio receiver is adaptable to a two-way oper-
ational activity through use of the "SEND/REC switch
(21, figure 3-1). With the receiver "RF GAIN" control
(11) turned clockwise from its "OFF" position, when
the a-c source is connected to the receiver, a-c power is
applied for either position of the "SEND/RECM switch.
When the switch is in its "SEND" position, the receiver
is disabled forprotection in the presence of a strong local
carrier such as that produced by local tranmission during
a two-way communication activity. When the switch is
in its "REC" position, the receiver provides for instant
reception.
1-21. When the radio receiver "FREQ CONTROL"
selector switch
'8, figure 3-1) is set to the "VFO" posi-
tion, the "TUNING" control (15) provides continuously
variable tuning of any desired carrier within the fre-
quency band selected by the "BAND CHANGE" switch
(17). When the "FREQ CONTROL" selector switch is
set to one of the "XTALS" positions, the receiver pro-
vides for fixed-frequency crystal-controlled reception of
any signal within the frequency range of 0.75 mc to 54.0
mc, provided that the proper crystal has been inserted
into the numbered crystal socket corresponding to the
selected switch position. The "BAND CHANGE" switch
functions as before, and the "TUNING" control is
used to adjust the r-f amplifier circuits to the operating
frequency. Exact tuning of the crystal-controlled first
heterodyne oscillator is provided by the "A FREQ
control
(7). The "TUNING LOCK" (14), when turned
clockwise, provides optional locking means for the ver-
nier dial (6), the main tuning dial (4), and the tuning
mechanism, to prevent
accidental detuning of the re-
ceiver due to vibration or accidental shift of the con-
trols. The "TUNING" control itself remains free to
turn even when the "TUNING LOCK is locked.
1-22. The receiver "SELECTIVITY" switch (22, fig-
ure 3-1) provides a choice of six degrees of bandwidth
or selectivity. The switch position chosen is that which
provides optimum receiver performance for the existing
quality of the received signal. When the switch is in one
of its "XTAL" positions, the "XTAL PHASING" con-
trol (23) is used to highly attenuate any interfering
signal, even when it is closely adjacent to the desired
signal. The receiver "LIMITER/OFF" switch (19) in its
"LIMITER" position provides for effectively reducing
ignition noise and other pulse-type noise from the re-
ceiver audio output.
1-23. The receiver "MOD/CW" switch (13, figure
3-1) in its "CW" position renders the bfo operative. The
"BEAT OSC." control (10) provides the means of ad-
justing the tone output within a frequency range of
23

T.8. 31 R2-4-1011-1 Section I

Section I
Paragraphs 1-24 to 1-29
T.O. 31R2-4-101-1
kc. The "BEAT OSC." control may be turned in either
direction on scale to provide the 3-kc range for the re-
ceived c-w signal. When the "MOD/CW" switch is in
the "MOD" position, the receiver provides for the recep-
tion of amplitude-modulated signals. When the receiver
is to be used for the reception of a frequency-shift sig-
nal, the "MOD/CW' switch position is dependent upon
whether the receiver i-f output or the receiver a-f output
is to be furnished to the associated frequency-shift con-
verter equipment. When the receiver i-f output is used,
the use of the bfo provides optional receiver output for
monitoring purposes. When the receiver a-f output is
used, the bfo must be in operation. When the receiver
is to provide suppressed-carrier (single or double side-
band) reception, the bfo is used to reinsert the carrier
at the receiver. For this application, the "BEAT OSC."
control is set to a position providing a bfo frequency of
455 kc.
1-24. The receiver "RF GAIN" control (11, figure
3-1) is adjustable to compensate for wide variations
encountered in the level of anv carrier received. To
maintain the receiver a-f output constant within narrow
limits for the "RF GAIN control setting chosen, the
receiver incorporates automatic volume control. The re-
ceiver "AVC/MANm switch (12), when set to the
"AVC" position, provides this action. Provisions are in-
cluded in the receiver for a-v-c operation even during
the reception of slow-speed telegraph signals. The
"RF GAIN" control is effective in either position of
the "AVC/MAN switch.
1-25. The receiver tuning meter
(1, figure 3-1) pro-
vides a tuning indication for the desired signal, when
the "AVC/MANm switch (12) is set to the "AVC"
position. When the "RF GAIN" control (11) is set
to its maximum clockwise setting, the meter top scale
indication is the ratio of the received signal level to a
signal of one microvolt, expressed in db. When the
"METER" switch (18) is held in its depressed "AF"
position, the meter bottom scale indication is the ratio
of the receiver audio output to the standard reference
output of six milliwatts, expressed in db.
1-26. OPERATIONAL THEORY.
1-27. GENERAL. An analysis of the operation of the
radio receiver is best evolved by considering the signal
path through the receiver r-f, i-f, and a-f sections, into
which the receiver may be considered theoretically sub-
divided. The self-contained power supply of the receiver
is considered separately. The simplified block diagram
(figure 1-2) indicates in block form the relationship
between the various sections of the receiver.
1-28. R-F SECTION. Ther-f section of the receiver pro-
vides selective circuitry for any selected signal within the
receiver frequency range of 0.54 to 54.0 mc. It does this
through the use of six sets of r-f tuner subassemblies
housed in a rotary turret assembly. Each set is used for
one frequency band of the receiver and comprises an an-
tenna r-f tuner, two identical interstage r-f tuners, and an
oscillator r-f tuner. The "BAND CHANGE" switch (17,
figure 3-1) provides for indenting the rotary turret as-
sembly so that the r-f tuner subassemblies for a particular
frequency band become part of the r-f section of the re-
ceiver. The antenna and two-stage r-f gain provided to
the signal assures that the signal-plus-noise to noise ratio
developed in the r-f section is high enough so that even
very weak signals provide useful receiver output. The
r-f section preselection assures that the gain available to
the signal is greatly in excess of that provided any un-
desired signal. Since the receiver utilizes the principles of
superheterodyne reception, a signal removed from the de-
sired signal by twice the 455-kc intermediate frequency
also provides an i-f signal acceptable to the i-f section of
the receiver. This image frequency, like any other unde-
sired signal, is greatly attenuated. However, for signals
tuned in on the three higher frequency bands of the re-
ceiver, the image frequency for an intermediate fre-
quency of 455 kc would be too close to the desired
signal. To maintain high image-rejection ratios, the re-
ceiver provides for double superheterodyne reception on
these bands. On the three lower frequency bands (below
7.4 mc), the signal tuned in is heterodyned to a 455-kc
i-f signal. On the three higher frequency bands, it is
first heterodyned to a 3955-kc i-f signal, which is then
heterodyned to a 455-kc i-f signal. With the receiver
"FREQ CONTROL" selector switch
(8) in its "VFO"
position, the receiver provides for continuously variable
tuning. When the switch is in one of its "XTALS" posi-
tions, the receiver first heterodyne variable oscillator is
replaced by a fixed-frequency crystal-controlled hetero-
dyne oscillator. Doing this results in receiver frequency
stability superior to that attainable for variable-
frequency tuning. Its use pre-establishes the communica-
tion channel, even when receiving conditions are poor,
without necessitating
a time-consuming search by the
operator.
1-29. I-F SECTION. The i-f section of the receiver in-
corporates the 455-kc i-f amplifier wherein practically
all of the overall gain and selectivity of the receiver is
developed. Also, it incorporates the single-double con-
version switch, which assumes its single or double con-
version position dependent on whether the rotary turret
is indented respectively for one of its three lower or
three higher frequency bands. For signals tuned in on
one of the three lower frequency bands, the signal has
access to the 455-kc i-f amplifier through a 455-kc i-f
gate. For this condition the switch renders the double-
conversion i-f channel inoperative. For signals tuned in
on one of the three higher frequency bands, the signal
reaches the 455-kc i-f amplifier through the 3955-kc i-f
double-conversion channel. For this condition the switch
renders the 455-kc i-f Kate inoperative. The six choices
of receiver selectivity
by the "SELECTIVITY
switch (22, figure 3-1) are developed in the 455-kc i-f
channel of the receiver. At the input to the 455-kc
i-f
amplifier is the 455-kc i-f crystal-filter circuit incorpo-
rated in the receiver. The use of the crystal filter enables
the receiver to attain the three degrees
of sharp "XTAL"
selectivity. The precise antibacklash gear-train tuning
mechanism provides for completely accurate resetability
and calibration accuracy of the receiver so that maximum

T.O. 3112-4-101-1
Section I
Paragraphs 1-30 to 1-35
benefit can be derived from the sharp, crystal passbands
of the 455-kc i-f crystal filter. The "XTAL PHASING
control (23) is part of the crystal filter. The 455
+ 3-kc
bfo and associated "BEAT OSC." control (10) and the
"IF OUTPUT" connector
(6, figure 2-2) are associ-
ated with the 455-kc i-f channel of the receiver.
1-30. A-F SECTION AND POWER SUPPLY. The a-f
section of the receiver incorporates an a-f amplifier to
develop the a-f power output of the receiver. The
"AUDIO GAIN" control (16, figure 3-1) is used to
control the receiver output to the "AUDIO OUTPUT"
terminals
(8, figure 2-2) and that to the "PHONES"
jack (20, figure 3-1). The self-contained power supply
develops all the a-c and the d-c supply voltages used by
the receiver. The critical d-c supply voltages are regu-
lated to maintain constant the sensitivity and frequency
stability. The "RF GAIN" control (11) is part of the
power-supply bias rectifier. Its chosen setting, in con-
junction with the a-v-c system of the receiver, when
used, determines the gain developed in the r-f and i-f
sections of the receiver.
two microvolts for an A-M signal, and 0.75 microvolt for
a c-w signal, or better. The undistorted power output of
the receiver at threshold sensitivity is two watts or better.
This a-f output is provided at a signal-plus-noise to
noise power ratio of ten to one. This provides for
optimum receiver performance in the presence of a weak
signal tuned in, since the background noise caused by
the first electron tube and the antenna r-f tuner does
not interfere with reception. The receiver sensitivity may
be reduced in the presence of a strong signal by turning
the "RF GAIN" control (11, figure 3-1) counterclock-
wise from its maximum clockwise position. This is done
to preven; overloading of the r-f and i-f sections of the
receiver. The receiver a-f output may be decreased by
turning the "AUDIO GAINcontrol (16) counterclock-
wise. This is done to prevent overloading of the a-f
section of the receiver and to provide for-comfortable
reception at the desired a-f output level. When the re-
ceiver a-v-c system is operative and the "RF GAIN"
control is set -to its maximum clockwise setting, the re-
ceiver output remains constant within a one-to-four volt-
age ratio when the input is increased from 2 to 200,000
1-31. CAPABlLlTlES AND LIMITATIONS.
&icrovolts. The use oiavc precludes excessive audio out-
1-32. GENERAL. The radio receiver provides optimum put when tuning through a carrier signal relatively
receiver performance when properly installed and oper- strong compared to the setting of the "AUDIO GAIN"
ated. The antenna input connector provides for connec- control, and compensates for the possible fading char-
tion to a balanced doublet or single-wire antenna sys- acteristics of the signal over long or short intervals of
tem. The 95-ohm cable used provides flexibility as to the time.
relative locations of the receiver and the antenna system.
In use, the receiver may be subjected to temperatures
within the range of O°C (32°F) to 60°C (140°F), at
relative humidities as high as 95 percent. After a 15-
minute warmup period, the frequency stability ranges
from 0.001 percent to 0.01 percent of the signal fre-
quency. The receiver incorporates advanced design and
shielding to reduce radiation characteristics to a mini-
mum. This enables the receiver to maintain performance
in multi-receiver installations and to comply with ship-
board regulations. The receiver embodies the necessary
chassis rigidity to withstand severe vibration and shock.
It is adequately treated with fungicidal varnish to con-
dition it for tropical use.
1-33. PRESELECTION. The image frequency of any
signal tuned in on the receiver is attenuated to the ex-
tent that if the desired signal strength were one micro-
volt, the strength of the image frequency signal would
have to be at least 4000 microvolts (at
7.4 mc) to de-
velop the same receiver output. At other signal fre-
quencies the strength of the image frequency signal
would have to be greater. Also, if the receiver is tuned
to 600 kc, a 455-kc signal input to the receiver will have
to be 2700 microvolts to produce the same effect as a one-
microvolt signal at 600 kc. For frequencies other than
600 kc, this 455-kc i-f rejection ratio of the receiver is
better. Likewise, the 3955-kc i-f rejection ratio of the
receiver is at least 50,000 for any signal frequency on
bands 4, 5, or 6, the frequency bands for which the 3955-
kc i-f channel of the receiver is operative.
1-34. SENSITIVITY. The receiver threshold sensitivity
(minimum signal input to develop its rated a-f output) is
1-35. SELECTIVITY. The bandwidth, or selectivity,
of the receiver is adjustable to provide for the reception
of a signal under varying conditions of propagation.
Since noise, regardless of its origin, is of the pulse type
and comprises all frequencies, the noise level in the
audio output of the receiver depends upon the overall
selectivity of the receiver. The "BROAD" settings of the
"SELECTIVITY" switch (22, figure 3-1) produce more
noise output than the "SHARP" settings. In the presence
of noise, it is advantageous to restrict the overall re-
ceiver bandwidth to the narrowest possible, consistent
with intelligible reception. However, the bandwidth rr-
quirements vary with the type of signal being received.
For phone reception, the i-f channel bandpass require-
ments are 455 kc
+ 2500 cps. This is also the require-
ment for single-tone telegraph reception. For keyed c-w
operation such as slow-speed telegraph, teletype (60
words per minute), and high-speed telegraph (400 words
per minute), the requirements are 455 kc
+- 50 cps, 455
kc
i: 75 cps, and 455 kc + 600 cps, respectively. When
two tones, one for "mark and another for "space", or
two channels are used, the bandwidth requirements are
doubled. The bandwidth requirements also depend upon
the frequency stability of the received signal and the
frequency stability of the receiver itself. For reception
of a c-w signal, a narrow bandwidth can be used. To
provide for reception of phone signals, the bandwidth
may be reduced to reduce noise output; however, the
use of a narrower bandwidth results in loss of the
higher-frequency audio components in the received sig-
nal and may impair the intelligibility of reception. To
provide for reception of telegraph or teletype signals,

Section I
Paragraphs 1-36 to 1-37
T.O. 31R2-4-101-1
full advantage should be taken of the "SELECTIVITY"
switch positions to reduce interfering noise. The "SE-
LECTIVITY" switch provides a choice of six degrees of
overall bandwidth. The sharp, crystal-derived band-
widths are 0.2 kc, 0.5 kc, and 1.3 kc. The broad, non-
crystal bandwidths are 3.0 kc, 8.0 kc, and 13.0 kc.
1-36. EQUIPMENT REQUIRED FOR PHONE OR
SLOW-SPEED TELEGRAPH RECEPTION.
1-37. The tabulation of the complete equipment re-
quired for reception of phone or slow-speed telegraph
signals is subdivided into two tables. The equipment
supplied and covered by this publication is listed in
table I. The components and auxiliary equipment of the
receiving system, required but not supplied, are listed
in table 11.
TABLE I. EQUIPMENT SUPPLIED
Government
Quantity Name Designation
1 Radio Receiver, Model
SP-600- JX-2 1
1 Plug, antennaconnector UG-102/U
1 Adapter, angle plug UG-lO4/U
1 Plug, i-f output connector PL-259
TABLE 11. COMPONENTS AND AUXILIARY
EQUIPMENT REQUIRED BUT NOT SUPPLIED
Government
Quantity Name Designation
* AR Crystal, Specification CR-18/U
MIL-C-3098
\d
1 Headset Navy Type
-49507
1 Cord, headset Navy Type
-49534
1 Loudspeaker LS-3
AR Cable, lead-in RG-22/U
1 Antenna system, bal-
anced doublet or
single wire
1 Source, a-c, single-
phase, 90 to 270V,
50 to 60 cps, 130
watts
*One crystal required for each operational signal fre-
quency.

PREPARATIQN FOR USE
_I 2-1. UNCRATING.
2-2. Carefully remove the receiver from its shipping
container, using the following procedure:
a. Remove the two steel straps from the wooden case.
b. Remove the cover nailed to the case.
c. Remove the excelsior from around the cartoned re-
ceiver.
d. Remove the cartoned receiver from the case.
e. Remove the waterproof tape from the folds of the
waterproof paper wrapped around the cartoned receiver,
and remove the waterproof paper wrapper.
f. Open the carton and remove the inner carton con-
taining the receiver.
g. Remove the vapor-proof bag from around the inner
carton.
h. Unflatten the corners of the inner carton, open it,
and remove the silica gel.
i. Remove the wood frame from the carton, and the
corrugated interiors comprising two side pieces, one
front, one back, and one top, each accordion folded.
j. Remove the receiver and set it out of the way in a
-a
convenient place near its final location.
k. Put all packing material in the wooden case and
store.
2-3. INSPECTION.
2-4. When the receiver has been removed from its
shipping container, carefully inspect it for any signs of
damage that may have occurred in shipment. Inspect the
front panel controls, the tuning dial windows, and the
meter for any defects. Inspect the tubes to make sure
that they are firmly seated in their sockets and that
none are broken. Inspect the fuses in the fuseholders on
the rear apron of the receiver to make certain that fuses
of the proper ratings are inserted in the fuseholders.
2-5. REPLACEMENT OF DEFECTIVE PARTS.
2-6. ELECTRON TUBES. If defective electron tubes are
discovered during inspection, replacement must be made
before operation is attempted. To replace defective elec-
tron tubes use the following procedure. (See figure
2-1.)
a. To remove electron tubes V17 and V19, the top-
hat-type tube clamp must first be removed. To remove
the clamp, press inward on the spring, while lifting the
clamp off the tube. Remove the tube by drawing it out
from its tube socket. Replace the top-hat clamp by seat-
ing it on the top of the tube so that the vertical bolt
adjacent
to it can be threaded through the hole in the
spring, with pressure providing a ratchet motion until
the clamp is firmly seated in place.
Section I1
Paragraphs 2-1 to 2-9
b. To remove electron tube V4, loosen the knurled
screw holding the tube shield. Then turn the tube shield
counterclockwise, while exerting inward pressure, and
remove the tube shield. The tube is of the pin type and
is removed preferably with a suitable tube remover.
c. To remove any electron tube other than V4, V17,
or V19, first removk the tube shield by twisting counter-
clockwise while exerting inward pressure. All tubes ex-
cept V17 and V19 are of the pin type, and are preferably
removed with an appropriate tube remover.
2-7. FUSES. To remove either the 1.6-ampere fuse or
the %-ampere fuse, located respectively in the "LINE
fuseholder (11, figure 2-2) and the "-B" fuseholder
(I) on the rear apron of the receiver, press in the top
of the fuseholder while turning it approximately 45 de-
grees in a counterclockwise direction. Removing the
pressure in this position will release the fuse which is
spring-clamped to the top of the fuseholder. The fuse
and the top of the fuseholder may now be pulled apart.
To replace either fuse, follow the reverse procedure.
Be certain to use fuses having the ratings speci-
fied above. Use of any other fuses may result
in damage to the receiver.
2-8. SETTING UP THE RECEIVER.
2-9. POWER TRANSFORMER CONNECTIONS.
When shipped, the power transformer primary tap of
the receiver is connected to operate from a 50- to 60-cps,
117-volt, a-c source. If the receiver is to be operated
from other than a 117-volt source, change the primary
tap connection. Table I11 shows the a-c source voltage
rating of each of the primary tap terminals, which are
TABLE Ill. POWER TRANSFORMER
TAP VOLTAGE RATINGS
Tap No. VoltageRating
2 95
3 105
4 117
5 130
6 190
7 210
8 234
9 260

Section II T.Q. 31 RIL-4-101-1
1. Electron tube V12
2.
Electron tube Vl6
3. Electron tube V15
4.
Electron tube V17
5. Electron tube V19
6. Electron tube V20
7.
"GND" terminal
8. "ANT input connector
9. Electron tube V1
Electron tube V3
Electron tube V2
Knurled thumbscrew
Retainer spring assembly
Crystal sockets
Electron tube
V5
Electron tube V13
Pilot lamp
Metal buttons
19. Electron tube V4
20. Electron tube V8
2 1. Electron tube V7
22.
Electron tube V6
23. Electron tube V9
24. Electron tube V10
25. Electron tube V18
26.
Electron tube V14
27.
Electron tube V11
Figure 2-1. Radio Receiver, Top View of Chassis

T.O. 3 112-4-101-1
Section I1
Paragraphs 2-10 to 2-1 1
identified by numerical designation on the bottom of
the power transformer (13, figure 2-2).
Choose the power transformer primary tap
whose voltage rating is closest to the available
a-c source voltage.
2-10. CRYSTAL SELECTION
AND MOUNTING.
When fixed-frequency, crystal-controlled operation is to
be utilized, the proper type CR-18/U crystal(s)'must be
obtained and inserted into the crystal socket(s) (14, fig-
ure 2-1). When ordering a crystal, the crystal frequency
and the signal frequency should be specified. For bands
1, 2, and 3, the crystal frequency can be calculated by
adding 455 kc to the signal frequency; for band 4, in
the signal-frequency range of 7.4 mc to 12.045 mc, the
crystal frequency can be calculated by adding 3955
kc
to the signal frequency; for signal frequencies above
12.045 mc, on bands 4, 5, and
6, the crystal frequency
can be calculated by adding 3955 kc to the signal fre-
quency and dividing the sum by three.
2-11. To mount the crystal units in the crystal sockets,
proceed as follows:
a. Loosen the knurled thumb&rew (12) on top of the
frequency-control unit, and push the retainer spring as-
sembly (13) to the rear.
b. Insert the crystals into the crystal sockets
(14),
numbered 1 through 6, on the frequency-control unit.
c. Bring the retainer spring assembly forward until
the springs are over the tops of the crystals in the
sockets, and tighten the knurled thumbscrew.
d. Using a pen or pencil, mark on the plastic chart
(9, figure 3-1) the signal frequencies for which the
crystals are intended.
1. "-B" fuse
7. "METER AD J AF" control
2. "DIOIIE OUTPUTterminals 8. "AUDIO OUTPUTterminals
3. "AVC" terminals
9. Power cord
, 4. "BFO INJ" control 10. "SPARE FUSES" cover
5. "METER ADJ RF" control
11. "LINE" fuse
6. "IF OUTPUT" connector 12. "AC" power receptacle
13. Power transformer
Figure 2-2. Radio Receiver, Rear View

Section II
Paragraphs 2-12 to 2-18
T.O. 31R2-4-101-1
2-12. INSTALLATION.
2-13. MOUNTING. The receiver is designed for rack
mounting in a standard 19-inch rack. The receiver front
panel is 10% inches high. Mount the receiver in a posi-
tion which permits the free access of air.
2-14. POWER. Make sure that the primary-tap lead
at the bottom of the power transformer is connected to
the tap which most nearly agrees with the 50-cps to 60-
cps power source voltage; refer to paragraph 2-9. Plug
the receiver into the power source using the receiver
power plug.
2-15. ANTENNA AND GROUND CONNECTIONS.
The antenna input circuit of the receiver is designed to
accommodate a balanced doublet or single-wire antenna
installation; however, other suitable antenna systems
specifically designed for the desired operating frequency
may be used. The input impedance of the receiver is
designed to match a 95-ohm transmission line. Con-
nect the antenna to the "ANT" input connector
(8, fig-
ure 2-1) using type RG-22/U cable, a type UG-104/U
angle plug adapter, and a type UG-102/U connector
plug. Figure 2-3 illustrates the antenna-cable fabrica-
tion procedure. If a single-wire antenna installation is
to be used, connect the antenna lead-in wire to one
terminal of the connector plug and a ground lead from
the other terminal of the connector plug to the receiver
"GND" terminal
(7). In all installations, bond the re-
ceiver "GND" terminal to the installation ground, us-
ing a suitable bonding strap.
2-16. HEADSET. For monitoring purposes, plug a
headset into the "PHONES" jack (20, figure 3-1).
Either a high-impedance or a low-impedance headset may
be used; however, the high-impedance (8000-ohm) type
is recommended.
2-17. LOUDSPEAKER. Connect a permanent-magnet,
dynamic-type, loudspeaker with a suitable 600-ohm
matching transformer across the "AUDIO OUTPUT"
terminals (8, figure 2-2). Por applications requiring
the insertion of d-c control or indicating voltages, re-
move the jumper connecting the two balanced sections
of the 600-ohm output at the "AUDIO OUTPUT" ter-
minals, and connect the insertion circuit in its place.
When the 600-ohm output is not used, connect
a 600-ohm, 2-watt resistor across the "AUDIO
OUTPUT" terminals to avoid component dam-
age from high transient peak voltages.
2-18. RECEIVER INTERCONNECTIONS FOR
DIVERSITY RECEPTION.
a. Receiver interconnections for space-diversity recep-
tion of phone signals are shown in figure 2-4. Connect
the "AVC" terminals (3, figure 2-2) designated
"6"
on each receiver to a common ground and interconnect
the "AVC" terminals designated
"-" on the two re-
ceivers. Open the jumpered "DIODE OUTPUT" ter-
minals (2) on one of the receivers, and connect the
C ING BACK SHELL FRONT SHELL
Cut end of cable even. Remove vinyl jacket 1-1/8 in.
Bare
5/8 in. of conductors. Tin exposed conductors and braid.
Slide coupling ring on cable. Screw back shell on cable. Sol-
der hole should align with conductors asshown.
Assemble front shell to back shell. Solder holes
in both front
and back shells should align. Solder braid to shells through
solder holes. Solder conductors to contacts.
Do not use ex-
cessive heat.
For final assembly,screw coupling ring on back shell.
Figure 2-3. Fabrication of Antenna Cable
10

Section II
Figure 2-4. Receiver lnterconnections far Phone Space-diversity Receiving System
Figure 2-5. Receiver lnterconnections for Space-diversity D-C Output Receiving System
UMPER REMOVED
SP-600-JX-21
SP-600-JX-21
600 OHMS
2 WATTS
-
-
TAPE INK
RECORDER

Section I1 T.O. 31 R2-4-101-1
SP-600-JX-21
SP-600-JX-21
---- INDICATES CONNECTIONS FOR
A-F SIGNAL OUTPUT
l NDICATES CONNECTIONS FOR
I-F SIGNAL OUTPUT
INDICATES CONNECTIONS COMMON
TO BOTH SYSTEMS
RADIO TELETYPE
TERMINAL
EQUlPMENT
I
L----------------a
Figure 2-6. Receiver lnterconnecfions for Frequency-shift Space-diversity Receiving System
"DIODE OUTPUT" terminals designated "-" to the the receivers, and connect the "DIODE OUTPUT" ter-
u
like terminal of the second receiver. Connect the loud- minal designated
"-" to the like terminal of the second
speaker across the "AUDIO OUTPUT" terminals (8)
receiver. Connect the three interconnected "DIODE
of the second receiver. OUTPUT" terminals to the associated recording equip-
ment.
b. For space-diversity reception of c-w signals, inter- c. The interconnections required for space-diversity
connect the two receivers as shown in figure 2-5- Open reception of frequency-shift carrier signals are shown
the jumpered "DIODE OUTPUT terminals of one of in figure
2-6. Interconnect the "AVC" terminals of the

T.O. 31112-4-101-1
Section II
Paragraphs 2-19 to 2-20
COUPLING RING PLUG SUB-ASSEMBLY
Cut end of cable even. Remove vinyl jacket
1-1/8 in.
Bare
5/8 in. of centerconductor. Trinibraided shield. Slide
coupling ring on cable. Tin exposed center conductor and
Screw the plug sub-assembly on cable. Solder assembly to
braid through solder holes. Use enough heat to create bond
of braid to shell. Solder center conductor to contact.
Forfinalassembly, screwcoupling ringon plug sub-assembly.
Figure 2-7. Fabrication of I-F Output Cable
two receivers as per step "a" of this paragraph. Keep
the jumpers across the "DIODE OUTPUT" terminals of
the receivers. Connect the frequency-shift converter
equipment to the "AUDIO OUTPUT" terminals of each
L
receiver if an audio signal is to be applied to the associ-
ated terminal equipment, or if a 455-kc signal is to be
used, connect the "IF OUTPUT" connector
(6, figure
2-2) of each receiver to the associated frequency-shift
converter equipment, using RG-11/U cable and PL-259
plugs. For fabrication instructions applicable to the i-f
output cable, refer to figure
2-7.
2-1 9. TESTING.
2-20. When the equipment has been installed, check
the complete installation for proper operation. Turn the
receiver on by rotating the "RF GAIN" control (11, fig-
ure 3-1) in a clockwise direction from its "OFF" posi-
tion and set the "SEND/REC" switch
(21) to its "REC
position. Allow the receiver to warm
up for 15 minutes.
Then check the operation of the receiver in the various
possible modes of operation on each of the six bands,
following the operating procedures outlined under para-
graph
3-25 as applicable.

Section Ill
Paragraphs 3-1 to 3-13
T.O. 31R2-4-101-1
OPERATION
3-1. GENERAL.
3-2. For optimum receiver performance, proper operat-
ing procedures must be observed. The complexity of the
operating procedures depends primarily upon the type
of signal to be received, and also upon the quality of the
communications link between transmitter and receiver.
The receiver is adjusted for its various modes of oper-
ation by means of the appropriate operating controls.
3-3. DESCRIPTION OF CONTROLS.
3-4. The controls used in normal receiver operation
are all located on the front panel and are shown in
figure 3-1. All references to the controls conform to
the front panel designations.
3-5. POWER. A-c power is applied to the receiver cir-
cuits by rotating the "RF GAIN" control (ll), clock-
wise from its "OFF" position. The power switch is an
integral part of the "RF GAIN control assembly and
its actuation is indicated by an audible click and by the
illumination of the main tuning dial (4) and the vernier
dial
(6).
Once power has been applied to the receiver,
do not switch it off momentarily and then back
on. The high initial filter-capacitor charging
current may cause the %-ampere fuse to fail.
3-6. "SEND/RECW.The "SEND/RECWswitch (21) dis-
ables the r-f section of the receiver when actuated to the
"SEND" position. This position is used during trans-
mission intervals in a two-way communication system to
prevent possible damage to the receiver from the strong
local transmission. When the switch is returned to its
"REC" position, normal receiver operation is restored.
3-7. "BAND CHANGE". The "BAND CHANGE"
switch (17) is used to select the frequency band which
includes the desired signal.frequency. The selected band
is indicated at the "MEGACYCLES" window (5) and
the top of the main-dial movable pointer (2) is auto-
matically positioned to indicate the main-tuning-dial
frequency band being used.
3-8. "TUNING". For variable-frequency operation,
the "TUNING" control (15) is used to tune the r-f
amplifier section of the receiver and the variable-
frequency first heterodyne oscillator to provide for re-
ception of the desired signal. In the fixed-frequency,
crystal-controlled mode of operation, a separate fixed-
frequency, crystal-controlled first heterodyne oscillator
is used, and the "TUNING" control is used to tune
only the r-f circuits for acceptance of the desired signal.
The "TUNING control drives the vernier dial (6),
visible through the window at the right side of the front
panel, and the main tuning dial (4) to indicate the fre-
quency selected.
3-9. "TUNING LOCK". The "TUNING LOCK (14),
when turned in a clockwise direction, clamps the vernier
dial (6), the main tuning dial
(4), and the tuning mech-
anism at the desired setting. The "TUNING" control
(15) remains free to turn. The "TUNING LOCK pre-
vents accidental detuning of the receiver due to severe
vibration or accidental shifting of the "TUNING con-
trol.
3-10. "FREQ CONTROL". The "FREQ CONTROL"
selector switch
(8) establishes the mode of operation of
the first heterodyne oscillator section of the receiver
and also, when set to its various "XTALS" positions,
establishes the oscillator frequency. When the "FREQ
CONTROL" selector switch is set to the "VFO" posi-
tion, the variable-frequency first heterodyne oscillator is
selected, and its frequency is determined by the setting
of the "TUNING" control (15). When the "FREQ
CONTROL" selector switch is set to any of its six
"XTALS" positions, a separate fixed-frequency, crystal-
controlled first heterodyne oscillator is selected. The
frequency of the oscillator is determined by the fre-
quency df the crystal inserted into the numbered crystal
socket corresponding to the selected switch position.
3-11.
''A FREQ". The "A FREQ" control (7) is used
to tune the crvstal selected bv the "FREQ CONTROL"
-
selector switch (8) precisely to the proper frequency.
The calibration of the
"A FREQ control is arbitrary;
however, advancing the control from the "HIGH" set-
ting to the "LOW" setting decreases the frequency of
oscillation. The crystals employed have a frequency tol-
erance of
0.005 percent, and the "A FREQ" control
has adequate range to compensate for deviations in
crystal frequency within these limits.
3-12. "RF GAIN". The "RF GAIN" control (ll),
when turned from its "OFF" position, is used to control
the gain of the r-f and i-f sections of the receiver. When
the control is turned to the "OFF" position, the a-c
power switch associated with the control removes power
from the receiver as described in paragraph 3-5. The
"RF GAIN" control functions in either position of the
"AVC/MAN" switch (12).
3-13. "AVC/MAN7'. The "AVC/MANU switch (12)
establishes the type of gain control used in the r-f and i-f
sections of the receiver. When the switch is actuated to
the "MAN position, the gain of the r-f and i-f sections
is established by the "RF GAIN" control (11) alone.
In the "AVC" position of the switch, a delayed a-v-c
system of control is selected. For any fixed setting of
the "AUDIO GAIN" control (16), the receiver output

T.O. 31 R2-4-101-1
Section Ill
Paragraphs 3-14 to 3-17
is maintained reasonably constant at a level predeter-
mined by the "RF GAIN" control setting, provided
that the input signal level is sufficient to overcome the
delay voltage in the a-v-c system. A minimum carrier
level of two microvolts at the receiver antenna input
connector is required for normal a-v-c operation.
3-14. "AUDIO GAIN". The "AUDIO GAIN" control
u
(16) is used to provide comfortable headset and/or
loudspeaker reception or to provide the means for ad-
justing the audio output to a level suitable for operat-
ing auxiliary equipment associated with the receiver.
3-15. "SELECTIVITY". The "SELECTIVITY" switch
(22) has six positions which establish receiver band-
widths of 0.2 kc,
0.5 kc, or 1.3 kc ("XTAL"), or 3 kc,
8 kc, or 13 kc ("NON-XTAL"). A crystal filter incorpo-
rated in the i-f section of the receiver is utilized in the
three "XTAL" positions of the "SELECTIVITY" switch.
In the three "NON-XTAL" positions, the crystal filter
is shorted out. The three "XTAL" positions provide
narrow bandwidths useful in the rejection of adjacent-
channel interference and are used under conditions of
extreme interference where quality or fidelity of the re-
ceiver output is secondary to continuity of service.
3-16. "XTAL PHASING". The "XTAL PHASING"
control (23) is part of the crystal filter referred to in
paragraph
3-15, and functions only when the "SE-
LECTIVITY" switch (22) is set to one of its three
"XTAL" positions. When adjacent-channel interference
is encountered, the "XTAL PHASING" control is ad-
justed in conjunction with the "SELECTIVITY" switch
to provide attenuation of the interfering carrier.
3-17. "LIMITER/OFF". The "LIMITER/OFF" switch
(19) is used under conditions of ignition or similar
pulse-type noise interference. When the switch is set to
the "LIMITER" positions, the limiter circuit in the re-
ceiver is operational, and noise (and desired audio) is
removed from the receiver outpllt for the interval of
each noise pulse. The internal limiter circuit is disabled
by actuating the switch to its "OFF" position.
1. Tuningmeter
2. Movable pointer
3. Fixed pointer
4. Main tuning dial
5. "MEGACYCLES" window
6. Vernier dial
7. "A FREQ" control
8. "FREQ CONTROL" selector switch
9. Plastic chart 16. "AUDIO GAIN" control
10. "BEAT OSC." control 17. "BAND CHANGE" switch
11. "RF GAIN" control 18. "METER" switch
12. "AVC/MAN" switch 19. "LIMITER/OFFWswitch
13. "MOD/CW" switch
20. "PHONES" jack
14. "TUNING LOCK" 21. "SEND/REC" switch
15. "TUNING" control
22. "SELECTIVITY" switch
23. "XTAL PHASING" control
Figure 3-1. Radio Receiver, Front Panel Controls and Indicators

Section Ill
Paragraphs 3- 18 to 3-24
T.O. 31 R2-4-101-1
3-18. "MOD/CW". The "MOD/CW" switch (13) is
3-22. PRESENTATIONS AND READINGS.
used to control operation of the internal bfo of the re-
ceiver. For reception of amplitude-modulated signals,
the "MOD/CWH switch is set to its "MOD" position
and the bfo is disabled. When the switch is operated to
the "CW" position, plate voltage is applied to the bfo
through the switch, and b-f-o operation is restored to
provide for the reception of unmodulated signals. Ad-
ditionally, a separate capacitor is switched into the a-v-c
circuit to increase the drcuit time constant and permit
a-v-c operation during c-w reception.
3-19. "BEAT OSC.". The "BEAT OSC." control (10)
is used to adjust the nominal 455-kc frequency of the
receiver bfo within the range of 23kc, thus providing
a variable tone output during c-w reception. The setting
of the control is optional, and is normally set to provide
the most intelligible reception. When set exactly to 455
kc, the control is useful for locating and tuning in weak
signals of any kind, as well as for carrier reinsertion at
the receiver when suppressed-carrier, single- or double-
sideband signals are being received. For the reception
of frequency-shift radio teletype signals, the "BEAT
OSC." control is adjusted to provide the proper "mark"
and "space" frequencies for the associated teletype
equipment. The bfo is operative only when the
"MOD/CW" switch (13) is in the "CW" position.
3-20. "METER". The "METER" switch (18) is used in
conjunction with the tuning meter (1) to obtain an in-
dication of the r-f signal input to the receiver and the
a-f output to a connected load. With the "METER"
switch in the normal
"RF" position, the "AVC/MAN"
switch (12) set to the "AVC" position, and the "RF
GAIN" control (11) set at maximum, the tuning meter
indication as read on the upper scale is the ratio of
the input signal level to a signal of one microvolt,
expressed in decibels. The meter "RF" indication also
provides a means for accurately tuning in an input sig-
nal. When the "METER switch is held in its depressed
"AF" position, the lower scale of the tuning meter indi-
cates in decibels the ratio of the receiver audio out-
put to a standard reference of six milliwatts.
Always turn the "AUDIO GAIN" control
(16) -fully counterclockwise and make certain
that the proper load is connected to the re-
ceiver before actuating the "METER" switch to
the "AF" position. Then, with the switch de-
pressed, slowly advance the "AUDIO GAIN"
control to its proper setting. Failure to observe
this precaution may result in damage to the
tuning meter.
3-21. "PHONES". The "PHONES" jack (20) provides
the means for connecting a headset to the audio output
section of the receiver. Either high-impedance or low-
impedance head phones may be plug-connected to the
receiver. The high-impedance type is recommended.
3-23. TUNING PRESENTATION. The main tuning
dial
(4, figure 3-1) and the vernier dial (6) are used to
accurately set the receiver to a desired signal frequency.
The main tuning dial has six frequency scales calibrated
in megacycles, and an arbitrary outer scale. The movable
pointer (2) is used to read the scale corresponding to
the frequency band chosen and the fixed pointer
(3) is used to read the arbitrary outer scale. The vernier
pointer is used to read the vernier dial (6), which has
an arbitrary 0-to-100 scale. The numeral under the fixed
pointer of the main tuning dial indicates the number of
revolutions that have been made by the vernier dial at
any setting. EXAMPLE: When the fixed pointer of the
main tuning dial indicates 4 and the vernier dial indi-
cates 87.6, the reading to log for this setting is 487.6.
The precise mechanical vernier system divides the rota-
tion of the main tuning dial over each frequency band
into approximately 600 vernier divisions, with one-half-
division calibration points. Since one-tenth divisions on
the vernier dial may be estimated accurately, each fre-
quency band is divided into approximately 6000 reada-
ble settings. Tnis permits extreme accuracy in the log-
ging of stations.
3-24. METER READINGS. When the receiver is used
for headset or speaker reception, the intelligibility of
reception can be determined aurally. When the receiver
is used for teletypewriter or telegraph recorded copy,
the intelligibility of reception can be determined vis-
ually. In either instance, when reception begins to de-
teriorate on a particular station frequency, the remote
station should be notified by mean; of ;he associated
transmitter so that the operational activity may be
switched to some other medetermined o~erationalfre-
quency. If accurate indications of the received carrier
strength or the receiver audio output are desired, the
tuning meter (1) may be used [~eferto paragraph
3-20 for the explanation of the function of the "ME-
TER" switch (18).] Table IV may be used to determine
the r-f microvolts or a-f mil1iwat;s equivalent to the db
readings of the r-f and a-f scale calibrations of the tun-
ing meter. With the "AUDIO GAIN" control
(16) set
to provide 500 milliwatts to a 600-ohm matching load,
TABLE IV. METER DECIBEL CONVERSION CHART
Dl3 R-F Microvolts DB
A-F Milliwatts
-6 0.5 -10 0.6