HP 415E Service manual

MODEL 415E
SWR METER
SERIALS PREFIXED: 719-
See Appendix I and II at rear of manual for:
a) 415E Options 01, 02, and
b) Serials Prefixed 530-, 545-

Model 415E
Lists of Illustrations and Tables
OF ILLUSTtATi
Number Title Page
1- 1 . Model 415E SWR Meter. 1-0
2- 1 . The Combining Case. 2-0
2-2. Steps to Place Instrument in
Combining Case. 2-0
2-3. Adapter Frame Instrument
Combinations. 2-1
2- 4. Two Half Modules in Rack Adapter . . 2-2
3- 1 . Front Panel Operating Controls
and Connector. 3-2
3-2. Rear Panel Operating Controls
and Connectors. 3-2
3-3. Typical SWR Measurement Setup ... 3-3
3-4. General Turn-On Procedure. 3-4
3-5. Expanded Section of Figure 3-6 ... 3-5
3-6. Converting Decibels to SWR. 3-6
3-7. Attenuation Measurement Setup ... 3-6
3-8. Impedance Measurement Rules
Summary. 3-7
3-9. Shift of Minimum with Load and Short . 3-7
3-10. Example for Use of Smith Chart ... 3-8
3-11. 415E Noise Figure Curves .3-10
3-12. Meter Noise Correction Curve .... 3-10
LIST OF
Number Title Page
1-1. Specifications. . . . . 1-0
3-1.
Panel Descriptions.
. . . . 3-3
5-1. Recommended Test Equipment . . . . . . 5-1
5-2. Performance Tests.
. . . . 5-3
5-3. Etched Circuit Soldering
Equipment.
. . . . 5-8
Number Title Page
4- 1 . Block Diagram. 4-1
5- 1 . Test Set Up. ! . '!!!!! 5-3
5-2. Examples of Diode Marking
Methods. 5-9
5-3A. Switch Component Location.5-10
5-3B. Switch Component Location.5-10
5-4. Transistor Biasing and Operating
Characteristics.5-12
5-5. Power Supply Waveforms (AC
Operation Only.5-14
5-6. Power Supply Waveforms (Initial
Battery Operation - Only).5-15
5-7. Signal Flow Waveforms (Input to
Amplifier Output).5-16
5-8. Meter and Output Waveforms .... 5-17
5-9. Schematic Notes.5-18
5-10. Circuit Board Component
Location.5-19
5-11. Power Supply and Input Circuit . . . . 5-19
5-12. Output and Meter Circuit.5-21
1-1. Battery - Cover Assembly. 1-1
I- 2. Connector Assembly. 1-1
II- l. Circuit Board Component Location-
Instruments Prefixed 530 . II-1
Number Title Page
5-4. Out-of-Circuit Transistor Resistance
Measurements. 5-12
5- 5. Ohmmeter Ranges for Transistor
Resistance Measurements. 5-12
6- 1 . Reference Designation Index. 6-2
6-2. Replaceable. 6-8
6-3. Code List of Manufacturers. 6-11
iii
02152-3

Section I Model415E
Figure 1-1 and Table 1-1
Figure 1-1. Model 415E SWR Meter
Table 1-1. Specifications
Sensitivity: 0.15 pv rms at maximum bandwidth
(1 pv rms on high impedance crystal input).
Noise: At least 7.5 db below full scale at rated sen¬
sitivity and maximum bandwidth with input termi¬
nated in optimum source impedance (see Input).
Noise figure less than 4 db.
Range: 70 db in 10 and 2 db steps.
Accuracy: ±0.05 db/10 db step; maximum cumula¬
tive error between any two 10-db steps, ±0.10 db;
maximum cumulative error between any two 2-db
steps, ±0.05 db. Linearity: ±0.02 db on expand
scales, determined by inherent meter resolution on
normal scales.
Input: Unbiased low and high impedance crystal (100
and 5000 ohm optimum source impedance respec¬
tively); biased crystal (1 v into IK); low and high
current bolometer (4.5 and 8.7 ma ±3% into 200 ohms),
positive bolometer protection. Input connector, BNC
female.
Input Frequency: 1000 cps, adjustable 7%. Other
frequencies between 400 and 2500 cps available on
special order.
Bandwidth: Variable, 15 to 130 cps. Typically less
than 0. 5 db change in gain from minimum to maxi¬
mum bandwidth.
Recorder Output: 0 to IV, 1000 ohms source imped¬
ance, BNC female.
Amplifier Output: 0to0.3Vrms (NORM), 0to0,8rms
(EXPAND) into at least 1 OK ohms, dual banana jacks.
Meter Scales: Calibrated for square-law detectors.
SWR: 1 to 4, 3.2 to 10 (NORM); 1 to 1.24 (EXPAND).
DB: 0 to 10 (NORM); 0 to 2.0 (EXPAND). Battery:
charge state.
Meter Movement: 0.25% movement, taut-band sus¬
pension, mirror-backed scale with expanded db and
swr scales greater than 4-1/4 in. (108 mm) long.
Power: 115 or 230 volts ±10%, 50to 400cps, 2watts.
Power line frequency or multiples thereof must not
be at the tuned amplifier frequency. Optional re¬
chargeable battery provides up to 36 hours contin¬
uous operation.
Dimensions: 7-25/32 in. wide, 6-3/32 in. high, llin.
deep from front side rail (190 x 155 x 279 mm).
Weight: Net 7-7/8 lb (3, 5 kg), 9-7/8 lb (4, 4 kg) with
battery.
Options:
01. Rechargeable battery installed.
02. Rear-panel input connector in parallel with the
front-panel connector.
1-0
02152-2

Model 415E
Section I
Paragraphs 1-1 to 1-7
SECTION 1
GENERAL INFORMATION
1-1. INTRODUCTION.
1-2. The Model 415E SWR Meter is a high-gain ampli¬
fier, tuned to an audio frequency, with a square-law
calibrated meter readout. The Model 415E is designed
for use with square-law detectors in the measurement
of SWR and attenuation. In addition, because of the
high-sensitivity and tuned amplifier, it can be used as
a null detector for audio frequency bridges. The Model
415E is shown in Figure 1-1. Operating Specifications
for the Model 415E are given in Table 1-1.
1-3. The Model 415E is a tuned audio amplifier de¬
signed to operate at a mean center frequency of 1000 cps
(Hz), adjustable 7% with a variable bandwidth of from
15 to 130 cps (Hz). Operating center frequency and band¬
width are both variable at instrument front panel.
Tuned amplifier gain is only slightly changed due to
any change in bandwidth and is typically less than 0.5 ab.
In addition to the front panel meter readout provided
by the SWR Meter, two rear panel outputs are also
available: An AC amplifier output is provided to allow
using the 415E as a high-gain (126 db) tuned amplifier;
a DC recorder output providing a convenient means of
obtaining a permanent record of measurement data.
Either or both of these rear panel outputs can be used
without affecting instrument meter operation provided
power line ground is not connected to the instrument
through either rear panel connector.
1-4. INSTRUMENTS COVERED BY MANUAL.
1-5. This manual applies directly to the Model 415E
SWR Meters having serial numbers prefixed 719 (first
three numbers of serial number). If the serial prefix
on your instrument is other than 719, there are differ¬
ences between the manual and your instrument which
are described in a Manual Changes sheet included with
the manual. If the manual changes sheet is missing,
the information can be supplied by your nearest Hewlett-
Packard Sales and Service Office (see lists at the rear
of this manual). The manual change sheet may also
include an "ERRATA” section which describes manual
correction information which applies to the manual for
all instruments including instruments prefixed 719.
1-6. INSTRUMENT OPTIONS.
1-7. This manual provides operating and servicing
information for the standard Model 415E. In addition,
operating and servicing information for Model 415E
instruments with Options 01 and/or 02, described be¬
low, is also included.
a. Option 01: Factory installed, 24-volt recharge¬
able battery capable of supplying up to 36 hours con¬
tinuous operation of the Model 415E. If not initially
installed as an option, the same battery is available
on order from Hewlett-Packard (see Paragraph 2-17).
b. Option 02: Additional input connector on rear
panel wired in parallel with the front panel INPUT con¬
nector. If not initially installed as an option, the con¬
nector - cable assembly is available on order from
Hewlett-Packard (see Paragraph 2-17).
02152-4
1-1

Section II
Figures 2-1 and 2-2
Model 415E
Figure 2-1. The Combining Case
[twist divider to vertical
POSITION
INSERT DIVIDER, ENGAGING
TABS IN TOP AND BOTTOM
MOUNTING SLOTS
©
GING
TOM
-OTS
©
PUSH IN TO LIMIT
©
SLIDE LATCH TO LOCK
DIVIDER
n—.
. *
/ g”T asL~" CE
,L=S===1
\\
=> aS> t ™ . \
PUSH RETAINER DOWN
TO RELEASE
©
TO SET RETAINER BACK IN
PLACE, ENGAGE HOOKS FIRST
ON ONE SIDE OF DIVIDER,
THEN ON OTHER
®
PUSH RETAINER UP TO LOCK
Figure 2-2. Steps to Place Instrument in Combining’Case
2-0
02152-1

Model 415E
Section II
Paragraphs 2-1 to 2-16
SECTION II
PREPARATION FOR USE
2-1. INCOMING INSPECTION.
2-2. This instrument was inspected both mechanically
and electrically before shipment. To confirm this, the
instrument should be inspected for physical damage in
transit. Also check for supplied accessories, and test
the electrical performance of the instrument, using
the procedure outlined in Paragraph 5-3. If there is
damage or deficiency, see the warranty on the inside
front cover of this manual.
2-3. INSTALLATION.
2-4. The Model 415E is fully transistorized; therefore
no special cooling is required. However, the instru¬
ment should not be operated where the ambient tem¬
perature exceeds 55 °C (140°F).
2-5. RACK MOUNTING.
2-6. The Model 415E is a submodular unit that when
used alone can be bench mounted only. However, when
used in combination with other submodular units it can
be bench and/or rack mounted. The hp combining case
and adapter frame are designed specifically for this
purpose.
2-7. COMBINING CASE. The combining case is a
full-module unit which accepts varying combinations
of submodular units. Being a full-module unit, it can
be bench or rack mounted analogous to any full-module
instrument. An illustration of the combining case is
shown in Figure 2-1. Instructions for installing the
Model 415E in a combining case are given graphically
in Figure 2-2.
2-8. ADAPTER FRAME. The adapter frame is arack
frame that accepts any combination of sub-modular
units. It can be rack mounted only. An illustration of
the adapter frame is given in Figure 2-3. Instructions
are given below:
a. Place the adapter frame on edge of bench as shown
in step 1, Figure 2-4.
b. Stack the sub-modular units in the frame as shown
in step 2, Figure 2-4. Place the spacer clamps be¬
tween instruments as shown in step 3, Figure 2-4.
c. Place spacer clamps on the two end instruments
(see step 4, Figure 2-4) and push the combination into
the frame.
d. Insert screws on either side of frame, and tighten
until sub-modular instruments are tight in the frame.
e. The complete assembly is ready for rack mounting.
2-9. THREE-CONDUCTOR POWER CABLE.
2-10. To protect operating personnel, the National
Electrical Manufacturers’ Association (NEMA) rec¬
ommends that the instrument panel and cabinet be
grounded. All Hewlett-Packard instruments are
equipped with a three-conductor power cable which,
when plugged into an appropriate receptacle, grounds
the instrument. The offest pin on the power cable
three-prong connector is the ground wire.
2-11. To preserve the protection feature when oper¬
ating the instrument from a two-contact outlet, use a
three -prong to two-prong adapter and connect the green
pigtail on the adapter to ground.
2-12, PRIMARY POWER REQUIREMENTS.
2-13. The Model 415E can be operated from an AC or
DC primary power source. The AC source can be either
115 or 230 volts, 50 to 400 cps. The DC source is a
24-volt rechargeable battery. The rechargeable bat¬
tery is supplied with option 01 instruments only.
2-14. For operation from AC primary power, the in¬
strument can be easily converted from 115- to 230-
volt operation. The LINE VOLTAGE switch, SI, a
two-position slide switch located at the rear of the in¬
strument, selects the mode of AC operation. The line
voltage for which the instrument is set to operate ap¬
pears on the slider of the switch. A 1/16-ampere, 250
volt fuse is used for both 115- and 230-volt operation.
CAUTION
DO NOT CHANGE THE SETTING OF THE
LINE VOLTAGE SWITCH WHEN THE IN¬
STRUMENT IS OPERATING.
2-15. INITIAL BATTERY CHECK.
2-16. The following applies to option 01 instruments
or instruments that have field - installed batteries.
When the battery is used as the power source for the
first time, perform the following steps:
Figure 2-3. Adapter Frame Instrument Combinations
02152-1
2-1

Section II
Paragraphs 2-17 to 2-20
Model 415E
©
ADAPTER
FRAME
Figure 2-4. Two Half Modules in Rack Adapter
a. Connect Model 415E to AC source. Set POWER
switch to CHARGE and charge battery for a minimum
of 16 hours or overnight. Note: the battery can be
maintained in the charging state indefinitely without
damaging the battery. It will assume its full capacity,
1.25 ampere hour, and no more.
b. Set POWER switch to TEST position, the meter
needle indication should be within the”BAT. CHARGED”
area (see Figure 3-1).
2-17. INSTALLING BATTERY AND INPUT
CONNECTOR.
2-18. Available from Hewlett-Packard are parts re¬
quired for modifying any Model 415E to correspond to
those instruments with Option 01 and/or Option 02. A
rechargeable Battery Installation Kit, hp Part Number
00415-606, contains the battery and necessary hard¬
ware for installation (corresponds to Option 01). In¬
stallation instructions are detailed in Appendix at rear
of this manual. To obtain the parts required for an
input connector on the rear panel (corresponding to
Option 02), order by hp Part Number as found in Table
6-1 (listed under Option 02). Instructions for instal¬
lation of this additional connector are detailed in Ap¬
pendix at rear of this manual.
2-19. REPACKAGING FOR SHIPMENT.
2-20. When returning an instrument to the Hewlett-
Packard Company, use the original packing material
(if foam type) if available or contact an authorized hp
Sales Office for assistance. If this is not possible, first
protect the instrument surfaces by wrapping in heavy
Kraft paper or with sheets of cardboard flat against
the instrument. Then protect the instrument on all
sides (use approximately 4 inches of packing material
designed specifically for package cushioning), pack in
a durable container, mark container clearly for proper
handling, and insure adequately before shipping.
Note
When an instrument is being returned to the
Hewlett-Packard Company for service or re¬
pair, attach a tag to the instrument specifying
the owner and desired action. All correspon¬
dence should identify the instrument by model
number and the full (eight-digit) serial number.
2-2
02152-1

Model 451E Section III
Paragraphs 3-1 to 3-14
SECTION I!!
OPERATING INSTRUCTIONS
3-1. INTRODUCTION,
3-2. This section contains information and procedures
for operation of the Model 415E (from either AC or bat¬
tery power source) in making swr and attenuation
measurements. Also included is information on slotted
line techniques, instruction in the use of a Smith Chart
for plotting load impedance, and discussion of Model
415E noise performance with various source imped¬
ances and noise effect on meter indication.
3-3. FRONT AND REAR PANEL FIXTURES.
3-4. Figures 3-1 and 3-2 identify by number the front
and rear panel fixtures of the Model 415E. The des¬
criptions in Table 3-1 are keyed by number (1-12 for
front, 13-18 for rear) to the figures. Further infor¬
mation regarding the various settings and uses of the
controls, indicators, connections, and adjustments is
included in the procedures of this section. Information
on battery is found in Paragraph 3-6.
3-5. GENERAL OPERATING AND
MEASUREMENT CONSIDERATIONS.
3-6. BATTERY OPERATION.
3-7. The Model 415E may be operated from a battery
instead of the 115 or 230 volt AC supply (see Paragraph
2- 13). Battery operation requires some slightly dif¬
ferent procedures to prolong battery life and to ensure
proper results. The rechargeable nickel - cadmium
battery is factory installed if ordered as Option 01 (see
Paragraph 1-7). The same battery may be ordered
and installed later. To obtain this, order hp Stock
Number 00415-606, Rechargeable Battery Installation
Kit.
3- 8. INITIAL BATTERY USE. When the Model 415E
is to be battery operated for the first time, perform
the following steps:
a. Switch the Model 415E POWER switch to BAT-
TERY/TEST position and note meter pointer indication:
A meter pointer indication in the "BAT. CHARGED"
area indicates the internally battery properly charged
and ready for use: A meter pointer indication to the
left of the "BAT. CHARGED" area means that the
battery must be charged as described below.
b. Connect the Model 415E to AC power source. Set
POWER switch to BATTERY/CHARGE and charge the
battery for a minimum of 16 hours or overnight.
c. After at least 16 hours of recharge time, switch
POWER switch to BATTERY/TEST position and check
battery charge. If the battery charge indication is still
unsatisfactory, see Paragraph 5-35.
3-9. OPTIMUM BATTERY USAGE. It is recommended
that the Model 415E be operated by the battery for up
to 8 hours, followed by 16 hours of recharge. If con¬
tinuous battery operation is required for more than 8
hours, the recharge time should be double the oper¬
ating time. Continuous battery operation is possible
for up to 36 hours but this must be followed by a pro¬
longed recharge period.
3-10. BATTERY STORAGE. Storage of the battery at
or below room temperature is best. Extended storage
at high temperatures will reduce the cell charge but
not damage the battery if the storage temperature is
less than 140°F. It is suggested that the battery be
charged after removal from storage and before using
the Model 415E for battery operation.
3-11. GROUNDLOOP CURRENTS .
3-12. The 415E SWR Meter audio amplifier has high
sensitivity to low level signals. To reduce ground loop
currents, the 415E grounds are isolated by a 46.4 ohm
resistor. Ground loops occur when instruments are
connected to415E outputs and grounded through power
cords or rack mountings. Ground loops can be min¬
imized in the following ways:
a. Connect the 415E to instruments with floating-
inputs;
b. Connect the 415E to instruments with high input
impedance; Connect only the signal wire between in¬
strument and the 415E;
c. Operation at higher signal levels;
d. An Adapter on the power cord to float the instru¬
ment ground where not prohibited by safety regulations.
3- 13 . BANDWIDTH AND FREQUENCY SELECTION.
3-14. Two front panel adjustments are provided to op¬
timize operation of the Model 415E tuned amplifier.
The FREQ (frequency) control allows a total variation
of 7% of the center tuned frequency. When more than
one Model 415E is included in the same measurement
setup, the variable tuned frequency is used to set all
the instruments to the exact frequency modulating the
source. The high sensitivity and narrow bandwidth
of the amplifier make the Model 415E valuable as a
meter-indicating null detector for audio frequency
bridges. The BANDWIDTH adjustment varies the tuned
filter bandwidth from 15 to 130 cps. A narrow band¬
width is best for low level signals as this improves
the signal to noise ratio. A wide bandwidth would find
more use in fast sweep rate measurements.
02152-4
3-1

Section HI
Figures 3-1 and 3-2
Model 415E
4I5E-A-9
Figure 3-1. Front Panel Operating Controls and Connector
Figure 3-2. Rear Panel Operating Controls and Connectors
3-2
02152-1

Model 415E
Section in
Paragraphs 3-15 to 3-21
Table 3-1. Panel Descriptions
1. Selects desired 415E power source:BATTERY/
CHARGE position allows internal battery re¬
charge when power cord is connected to AC line,
2. Indicator lights when power switch is in LINE/
ON or BATTERY/CHARGE position.
3. Female BNC INPUT connector.
4. Set input of Model 415E for use with a bolom¬
eter or crystal detector mount. See Paragraph
3-53.
5. Adjustment allows center frequency variation
by 70 cps.
6. Attenuator adjusts gain in 10 db steps.
7. Allows full scale expansion of any 2.0 db portion
of the 10-db scale.
8. Changes bandwidth from 15 to 130 cps.
9. Allows initial meter reference setting with a
control range of at least 10-db.
10. Provides fine adjustment of GAIN control meter
settings.
11. Mechanical zero adjustment allows exact sett¬
ing of meter needle to 2.0 db calibration mark.
12. With POWER switch set to BATTERY/TEST, a
meter needle indication within the ’’BATTERY
CHARGE” area on the meter face (indicated by
12A) shows that internal battery is charged suf¬
ficiently for proper 415E operation; if needle
indicator is to left (area 12B) of "BATTERY
CHARGED” area, then battery is not charged
sufficiently for proper instrument operation
(option 01 - ONLY).
13. Additional input connector (wired in parallel
with front panel connector); supplied as Option
02 for 415E only upon request.
14. DC output for recorder use (0 to 1 volt into open
circuit or 1000 ohms).
15. AC output for use as tuned amplifier output.
16. Three-conductor AC power cord receptacle
(NEMA-type).
17. Contains power line fuse.
18. Slide switch to allow 115- or 230-volt AC
operation.
3-15. SWR MEASUREMENT EQUIPMENT
AND TECHNIQUES.
3-16. EQUIPMENT .
3-17. A typical setup of equipment used in SWR meas¬
urements is shown in Figure 3-3. The signal source is
usually square-wave modulated at 1000 cps since other
modulating waveforms often cause undesirable fre¬
quency modulation of the source. Harmonics from the
source sometimes cause trouble and can be eliminated
with a low-pass filter.
3-18. The detector should be a square-law device (out¬
put voltage proportional to RF power input) such as a
barretter or a crystal diode operated at low signal
levels. The meter of the 415E is calibrated for square-
law detectors. Crystal diodes are normally more sen¬
sitive than barretters but barretters are square-law
over a wider dynamic range. Both types of detector
normally maintain accurate square-law response up to
at least full scale deflection with the RANGE-DB switch
set to 30 position and coarse GAIN at maximum. (1 mv
RMS sine wave or 2.2 mv peak-to-peak square wave
causes full scale deflection on HIGH XTAL IMPED
position. On other positions of INPUT switch, 0.15 mv
RMS sine wave or 0.33 mv peak-to-peak square wave
causes full scale deflection.) Above this level these
detectors should be individually checked for departure
from square-law behaviour or manufacturer’s data
should be consulted.
02152-3
3-19. A short circuit termination is useful in establish¬
ing reference positions along the transmission line and
is measuring transmission line wavelengths.
3-20. SLOTTED LINE PROBE PENETRATION .
3-21. A general rule in slotted line measurement is to
use minimum probe penetration that still picks up ad¬
equate signal to measure. The probe couples to the
Figure 3-3. Typical SWR Measurement Setup
3-3

Section HI
Figure 3-4
Model 415E
GAIN
VERNIER
RANGE-08
EXPAND POWER
INPUT
XTAL IMPED-1 (-BOLOMETER
BIASED 4.5 MA
LOW B T MA
415 E SWR METER
HEWLETT • PACKARD
fZi INPUT FREQ f'i 8ANOWIOTH
4I5E-A -158
1. Set POWER switch to OFF. Meter pointer should
rest at 2 on the 0-2 DB scale (if not refer to Par¬
agraph 5-10).
2. Set POWER switch to LINE/ON (or BATTERY/
ON).
6. Adjust RANGE-DB, GAIN, and VERNIER controls
and the amplitude of the input signal for a con¬
venient meter reference near mid-scale.
7. Adjust FREQ control for maximum meter pointer
deflection.
K set to BATTERY/ON refer to Paragraph
3-5 and check battery potential.
3. Set INPUT to desired input impedance. (Note see
Paragraph 3-55.)
4. Connect audio source to INPUT (i.e., crystal de¬
tector, bolometer, audio oscillator, etc.).
5. Adjust modulation frequency (audio input signal)
to approximately 1000 cps.
8. A djust BANDWIDTH control: fully counterclock-
w i s e rotation is minimum bandwidth and fully
clockwise rotation is maximum bandwidth.
A narrow bandwidth is usually best for low
level signals; 30 cps is convenient for most
applications; and a wide bandwidth is usually
best for fast sweep rate measurements.
Figure 3-4. General Turn-On Procedure
3-4
02152-2

Model 415E
Section III
Paragraphs 3-22 to 3-24
transmission line as a shunt admittance which increases
(disturbing the transmission line more) as the probe
penetrates farther. To find out whether a given probe
penetration is too great or not, measure SWR, then
change probe penetration and remeasure SWR. If the
second reading is different, the probe is penetrating
too far and loading the transmission line significantly.
scale). Now move the probe toward a minimum. If the
meter drops below 3.2, rotate the RANGE-DB switch one
position clockwise and read on the 3.2 to 10 SWR scale.
If the pointer drops below this scale, rotate RANGE-DB
switch one more position clockwise and read on the 1.0
to 4 scale and multiply by 10. This pattern continues
for still higher SWR readings.
3-22. PROCEDURE .
3-23. MODERATE SWR. The scales of the 415E are
calibrated for reading standing wave ratio directly from
the meter. Set the slotted line probe at a voltage max¬
imum and adjust the gain of the 415E with the RANGE-
DB, GAIN, and VERNIER controls (EXPAND switch to
NORM) for full scale deflection (1.0 on the 1.0 to 4 SWR
3-24. The DB scales can be used for a standing wave
ratio measurement by setting the 415E to full scale at
a voltage maximum, then turning the RANGE-DB switch
clockwise for anon scale reading at a voltage minimum
and noting the difference in DB readings at the maximum
and minimum. A DB reading is obtained by adding
RANGE-DB switch setting and meter indication.
02152-2
Figure 3-5. Expanded Section of Figure 3-6
3-5

Model 415E
Section III
Paragraphs 3-25 to 3-32
3-25. LOW SWR. Standing wave ratio between 1.0 and
1.24 can be read quite accurately on the EXPAND scales
of the meter when the EXPAND switch is set to any
position other than NORM.
3-26. MODERATE SWR, HIGH RESOLUTION. The
EXPAND and -DB scale can be used together with the
EXPAND switch to read any SWR with high resolution
in DB. Figure 3-5 and 3-6 are used to convert DB to
SWR. The reference level (full scale meter deflection
at a voltage maximum) can be used with the EXPAND
switch at NORM (since 0 db NORM and 0 db EXPAND
correspond) but greater accuracy is obtained by setting
the reference level with the EXPAND switch to 0.
short- circuiting the transmission line are easy to lo¬
cate accurately). Compute the SWR from the following
formula:
SWR = Yir ( Xg /Ax).
3-29. TEN-TIMES-MINIMUM POWER METHOD. An¬
other convenient "level above minimum method" to
use for computing SWR is a level 10 db above minimum.
The separation (AX) between these positions should be
put in the following formula: A ,
SWR = M^Ax)
For standing wave ratios as low as 15 to 1, the accuracy
of this method is within 1%.
Figure 3-6. Converting Decibels to SWR
3-27. HIGH SWR. High standing wave ratios (greater
than 30, or sometimes 10) present problems because of
excessive probe penetration (to lift the minimum above
the noise level) and departure of detector behaviour
from square-law. Both problems are lessened or elim¬
inated by measuring only the standing wave pattern near
the voltage minimum, where probe loading effects are
least disturbing.
3-28. TWICE-MINIMUM POWER METHOD. The basis-
for this method (and the TEN-TIMES-MINIMUM POWER
METHOD) is the fact that for a high SWR, the standing
wave pattern approximates aparabola in the vicinity of
a voltage minimum. The slotted line carriage must have
a good scale or dial indicator. Measure the distance
(AX) between positions on the standing wave pattern
where the voltage is 3 db above the voltage at the min¬
imum. Also measure the transmission line wavelength
Ag (standing wave pattern minima are one-half wave¬
length apart and the sharp minima resulting from
3-30. SWR MEASUREMENT-SOURCES OF ERROR.
Several possibilities have already been mentioned:
excessive frequency modulation of source (smears out
sharp, deep nulls of high SWR pattern), harmonics of
signal frequency from source, departure of detector
from square-law behaviour, and excessive probe pen¬
etration. Also, reflections in the transmission line
between the slotted line and device being measured
must be minimized.
3-31. ATTENUATION MEASUREMENT.
3-32. The 415E may be used for high resolution in¬
sertion loss measurements simply by inserting the
device to be measured between signal source and de¬
tector and noting the change in DB indication on the
415E. A typical measurement is shown in Figure 3-7.
The continuous coverage of the EXPAND scales allows
any attenuation measurement to be made on the EX¬
PAND scales. For accurate results, both the signal
source and the detector should be well matched. Im¬
pedance match of source and detector can be improved,
if necessary, with padding attenuators, isolators, or
tuners.
Figure 3-7. Attenuation Measurement Setup
02152-2
3-6

Model 415E
Section III
Paragraphs 3-33 to 3-36
IF MINIMUM DOES NOT
SHIFT,LOAD EQUALS E 0 / S WR
Figure 3-8. Impedance Measurement Rules Summary
3-32. LOAD IMPEDANCE MEASUREMENT.
3-33. GENERAL.
3-34. Slotted line techniques provide information to
allow calculation of a load impedance. The following-
rules apply to the indications given by the voltage min¬
imum when the load is replaced by a short. Figure
3-8 summarizes and graphically presents these im¬
pedance measurement rules. When the load is replaced
by a short, then:
a. T he shift in the minimum is never more than
±1/4 wavelength.
d. Referring to Figure 3-9 and the following for
mulas, compute the normalized load impedance:
Normalized Zl =
1 - j(swr) Tan X
(swr) - j Tan X
where X =
180° (a Ad)
Ag / 2
b. If the minimum moves toward the load, the load
has a capacitive component.
c. If the minimum moves toward the generator, the
load has an inductive component.
d. If the minimum does not move, the load is com¬
pletely resistive and has a normalized value of 1/swr.
e. If the minimum shifts exactly one-quarter wave¬
length, the load is completely resistive and has a nor¬
malized value equal to the swr.
f. The minimum will always be at a multiple of a
half wavelength from the load.
3-35. IMPEDANCE MEASUREMENT PROCEDURE.
3-38. The procedure for performing the actual im¬
pedance measurement with a slotted line is as follows:
a. Connect the load under test to the slotted line
section and measure the swr (see Paragraph 3-26 or
3-28). Also note the position of the probe carriage at
the minimum.
b. Replace the load under test with a short.
c. Locate the minimum with the line shorted.
A d ■
Figure 3-9. Shift of Minimum with Load and Short
02152-2
3-7

Section III
Paragraphs 3-37 to 3-38
Model 415E
and: ±Ad = Shift in centimeters of the minimum
point when the short is used. Ad takes a positive
sign (+) if the minimum shifts toward the load.
Ad takes a negative sign(-)if the minimum shifts
toward the generator.
X «/2 = one-half guide wavelength, i.e., the
distance in centimeters between two adjacent volt¬
age minima.
Note
The above calculations are based on the as¬
sumption that no losses occur in the trans¬
mission line. It is assumed that the char¬
acteristic line impedance, Zq, is resistive.
3-37. SMITH CHART EXPLANATION.
3-38. When data is obtained from a slotted line sys¬
tem, one of the best aids for determining impedance
is the Smith Chart. * A Smith Chart with an example
(see Paragraph 3-39) is shown in Figure 3-10. The
values of resistance and reactance are based on a nor¬
malized value obtained by dividing the actual value by
the characteristic impedance, Zq, of the line. Thus
if Z = 5 +• j 25 ohms and if Zq = 50 ohms, then Zjg =
0.1 + j 0.5. On the Smith Chart, the circles which
are tangent to the bottom of the chart are for a con¬
stant, normalized resistance; lines curvingtothe right
from center are the normalized positive reactance
components; lines curving to the left from center are
the normalized negative reactance components; the
straight line forming the vertical diameter is aline of
zero reactance; the lower half of the zero reactance
line (marked 1 through 50) also represents the stand¬
ing wave ratio line.
* Smith, P. H. , "Transmission - Line Calculator, ”
E lectronics , Jan. 1939, McGraw-Hill.
3-8
Figure 3-10. Example for Use of Smith Chart
02152-2

Model 415E
3-39. SMITH CHART CALCULATIONS.
3-40. Use of the Smith Chart for calculating imped¬
ance is outlined below. Followingthe generalized pro¬
cedure is a numerical example. Other methods are
possible for first entering the Smith Chart, but the one
suggested here is practical and easy to use.
a. Determine the guide wavelength, A as explained
in Paragraph 3-28.
b. Measure the swr by the method in either Para¬
graph 3-26 or 3-28.
c. Locate a convenient minimum with the load still
in place. Record the probe carriage reading.
d. Replace load by a short, relocate the minimum
and record the probe carriage reading. Determine
A d, the difference between this reading and the one
from step c. Note whether the minimum was moved
toward the load or toward the generator.
e. Calculate the shift of the minimum, in terms of
wavelength:
f. Start at center of Smith Chart and draw a circle
with a radius equal to the swr.
g. Enter the Smith Chart at the top, move in the di¬
rection of probe movement noted in step d and a dis¬
tance AA, computed in step e. Use wavelength scale
at the periphery of the Smith Chart.
h. Draw a line from the A A point to the center of
the chart.
i. Locate the normalized impedance as the inter¬
section of the swr circle and the line drawn in step h.
j. The actual impedance is the product of the nor¬
malized impedance from step i and Zq, the line char¬
acteristic impedance.
Note
The convention of entering the chart as stated
in step g applies only if the minimum is lo¬
cated first with the load on the line and relo¬
cated when the line is shorted. If it is neces¬
sary to first establish the shorted minimum
point, the direction of A a would be opposite
to the direction of probe movement required to
relocate the minimum with the load concerned.
3-41. The following example will clarify the above pro¬
cedure. Figure 3-10 shows the important steps involv¬
ing the Smith Chart. The assumed characteristic im¬
pedance is 50 ohms. The distance between adjacent
minima is 15 cm, therefore A ff = 30 cm. The swr is
measured as 3.3. A minimum is located at 22 cm. The
load is shorted and the minimum shifts to 19 cm, toward
the generator.
Section III
Paragraphs 3-39 to 3-49
Ad = 22 cm - 19 cm = 3 cm
AA = Ad/ a D . = 3 cm/30 cm = 0.1 wavelength
3-42. The following numbered steps refer directly to
Figure 3-10.
(1) A circle for swr = 3.3 is drawn.
(2) A line is drawn from the 0.1 A point (toward the
generator) to the center of the chart.
(3) The normalized impedance at the intersection
of the circle and the line is 0.44 + j 0.63.
The impedance of the load (for Zq = 50ft) is then:
50 (0.44 + j 0.63) = 22 + j 31.5 ohms
3-43, SPECIAL APPLICATIONS.
3-44. The Model 415E is equipped with outputs which
allow applications other than as a meter indicating de¬
vice for swr or attenuation.
3-45. RECORDER.
3-46. The rear panel recorder output furnishes an out¬
put from Oto 1 volt DC with internal resistance of 1.000
ohms and provides a convenient means of obtaining a
permanent record of measured data. For proper op¬
eration, the recorder output ground (BNC shell) must
be connected to a floating ground. Adapters are com¬
monly available to float the ground of grounded input
instruments at the power cord (see Paragraph 3-11).
3-47. AMPLIFIER OUTPUT.
3-48. The rear panel amplifier output furnishes an
output from 0 to 0.8 volt RMS into lOKohms or more.
The Model 415E will supply up to 126 db of voltage gain.
For proper operation, the ground terminal (black) must
be connected to a floating ground (see Paragraph 3-11).
With the 415E EXPAND switch set to NORM, a full
scale meter reading will result in a 0. 3 volt RMS out¬
put signal, and a minimum scale reading (10 db) will re¬
sult in approximately 0.03 volt RMS. With the 415E EX¬
PAND switch set to any position except NORM, a full
scale meter reading results in a 0.8 volt RMS output
and a minimum scale reading (2 db) results in a 0.5
volt RMS output signal. A zero input signal results in
a zero volt output signal.
3-49. The Model 415E is especially useful as a tuned
amplifier in a measurement setup using an Oscilloscope
and a Sweep Oscillator. Sweep speeds may be increased
(over the speeds using a ratio meter in a reflectometer
system) and the Model 415E, used as a high gain amp¬
lifier, provides the required sensitivity.* The AM¬
PLIFIER OUTPUT (AC) is often more useful for this
purpose than the RECORDER OUTPUT (DC) since the
DC output is filtered to reduce ripple and its response
is too slow to make full use of maximum bandwidth.
* See hp Application Notes 54, 61, 65, and 66.
02152-2
3-9

Section HI
Paragraphs 3-50 to 3-51
Model 415E
3-50. MODEL 4!5i MOiSi FIGURE .
3-51, Figure 3-11 illustrates a typical value of Noise
Figure that would be encountered in a Model 415E.
The following example of Model 415E noise figure
measurement is presented to illustrate the particular
considerations that must be made to calculate instru¬
ment noise figure.
a. Calculate the meter indication when a 5000 ohm
resistor is connected as a source, assuming the Model
415E is noiseless (0 db noise figure).
b. Any excess indication of415E meter is then one-
half of its noise figure.
SOURCE IMPEDANCE(R S )
SOURCE IMPEDANCE (R s )
Figure 3-11. 415E Noise Figure Curves
c. C alculation example:
(1) Assume 415E with controls set for the following
conditions: EXTAL IMPED HIGH (input imped¬
ance 200K), 1 pv RMS sine wave at input causes
full scale deflection (Oon Oto 10 DB scale), 130
cps bandwidth at 3 db points (1.5 db points on
Model 415E meter which is calibrated for
square-law. Noise equivalent bandwidth is n/2
times 3 db bandwidth).
(2) The open-circuit noise voltage across a 5000
ohm resistor at 295° K (22°C) in a bandwidth of
(130 times n/2) cps is as follows:
V n = 2HKTBR
V n = 2]|(1.38 x 10“ 23 ) (295/130 xtt/ 2 ) (5000)
V n = 0.129 x 10“ 6 volts = 0.129 pv
(3) The 0.129pv open circuit voltage is reduced to
0.126 pv by the 200K ohm input resistance of
the 415E which is assumed to be noiseless.
(4) 0.126 pv is 18.0 db below 1 pv but square-law
calibrated meter of the 415E, set as above,
would indicate 1/2 of 18 db or 9.0 db below full
scale. Also, since the 415E meter is average¬
reading and calibrated to read RMS value of a
sine wave, it reads 1.05 db below the RMS value
of Gaussian noise. Therefore, the 415E reads
1/2 of 1.05 db or 0.525 db less than 9.0 and the
415E would read 9.525 db with a 5000 ohm
resistor connected to the input as described.
Hence, a 7.525 db (9.525 + 2) meter reading
indicates a 4 db noise figure.
2 4 6 8 10 12
SIGNAL PLUS NOISE MINUS NOISE ALONE {DB)
Figure 3-12. Meter Noise Correction Curve
3-10
02152-3

Model 415E
Section III
Paragraphs 3-52 to 3-56
3-52. A system error occurs when making meas¬
urements on lower 415E ranges due to noise. For con¬
venient reference, a graph (Figure 3-12) is shown to
allow correction to meter reading for any given meas¬
urement. To use this graph, make a signal measure¬
ment, then turn RF power source off or disconnect
detector from RF source and note average meter read¬
ing due to noise. The difference between these two
reading is used to obtain the proper correction factor
from Figure 3-12. For example: if the average noise
level is 9.5 db and the measured signal level is 3.5db
then the difference is 6 db. Refer to Figure 3-12, 6db
corresponds to an error of 0.1 db. This 0.1 db
correction factor is always added to measured signal.
Hence, 3.5+ 0.1 = 3.6 db (corrected meter reading).
3-53. USE OF CRYSTAL DETECTORS.
3-54. The input impedance of Model 415E must always
be higher than the output or source impedance of a
bolometer or crystal detector connected to the INPUT
connector (see Paragraph 4-21 for discussion). For low
output impedance devices, such as 100 to 200 ohm
detectors, use 415E XTAL IMPED/LOW switch posi¬
tion. For high output impedance devices, such as hp
Models 420B, 423B, 424B, or 786D, use 415E XTAL
IMPED/HIGH position. If improper input impedance is
selected, the crystal detector may depart from square-
law for which 415E is calibrated. Paragraph 3-55
gives method of checking and calibrating a detector for
square-law response.
3-55. CHECKING SQUAStS-LAW RESPONSE.
3-56. Increase the power level to the crystal detector
by known increments and note detector response on
415E. Note: a deviation in square-law response may
be due to excessive RF power to the crystal detector
(see Operating literature for specified response
characteristics of crystal detector in use).
02152-1
3-11/3-12

Model 415E
Section IV
Paragraphs 4-1 to 4-4
SICTiON l¥
PRINCIPLES OF OPERATION
4-1. GENERAL.
4-2 The 415E is a high-gain tuned amplifier which
takes an input from a bolometer, crystal, or any audio
source, amplifies it and applies it to a meter calibrated
for use with square-law detectors. With bolometer
or biased crystal operation, the Model 415E supplies
the appropriate bias current. Figure 4-1 is a block
diagram which illustrates instrument operation. Refer
also to the schematic diagrams, Figures 5-11 and 5-12
which fold out of the manual for easy reference.
4-3. INPUT CIRCUITS.
4-4. The input voltage is first routed through INPUT
switch, A1S1. In the HIGH position it is applieddirec-
tly to the first section of the range attenuator, A2S1.
When the INPUT switch is set to any other position but
HIGH, the input signal passes through transformer T1
whose turns ratio provides a 50 to 1 impedance trans¬
formation, converting a 50 to 200 ohm source to 2500
to 10,000 ohms (which is the range of best noise figure
for the INPUT AMPLIFIER).
I INPUT 1
AISI
rh
R3
IOOK
Figure 4-1. Block Diagram
02152-1
4-1

Section IV
Paragraphs 4-5 to 4-21
4-5. RANGE ATTENUATOR .
4-6. The signal from A1S1 is fed to the first section
of the RANGE- DB switch, A2S1, and then to the input
amplifier. The second section of A2S1 is located be¬
tween the input amplifier and the second amplifier.
The RANGE-DB Switch positions are marked in 10
db steps.
4-7. INPUT AMPLIFIER.
4-8. After passing through the first section of the
range attenuator, A2S1, the signal goes to the input
amplifier (A3Q1/Q2/Q3/Q4) which consists of four
transistors in cascade. The input signal is applied to
the base of A3Q1 and the final amplifier signal is taken
from the collector of A3Q4. The GAIN and VERNIER
controls are associated with this amplifier and vary its
gain over a range of more than 10 to 1. GAIN control
Rl, the coarse control, is a250Kohm variable resistor
which adjusts the amount of negative feedback from
the collector of A3Q4 to the emitter of A3Q1. VER¬
NIER control, R2, is a fine gain control and changes
gain by inserting 0 to 5000 ohms in series with the
output signal.
4-9. SECOND AMPLIFIER.
4-10. Transistors A3Q5 and A3Q6 amplify the signal
from the second section of the range attenuator. AC
feedback provides gain stability and high input im¬
pedance . The output of the amplifier is applied through
the EXPAND attenuator, A2S2, to the third amplifier
A3Q8 and A3Q9.
4-11. EXPAND CIRCUIT .
4-12. The function of the EXPAND switch A2S2, is to
allow any signal level to be measured on an expanded
scale with continuous coverage while maintaining the
original reference level. Expansion is accomplished
by applying a precise amount of DC-offset current from
A3Q17 to the meter and simultaneously increasing the
signal to the 3rd amplifier. This increased gain allows
a 2 db change in signal level to deflect the meter across
its full scale. The offset current places the zero signal
indication off scale to the left.
4-13. FREQUENCY SELECTIVE CIRCUITS.
4-14. The frequency response of the third amplifier,
A3Q8 and A3Q9, is shaped by negative feedback. The
feedback path includes a Wien-bridge and amplifier
A2Q7. At the null frequency of the Wien-bridge, the
negative feedback path is open and the gain of the am¬
plifier is maximum. Off center frequency the negative
feedback through the Wien-bridge reduces gain. The
amount of the "off resonance" gain reduction depends
on the setting of the BANDWIDTH control, R3.
4-15. The Wien-bridge is adjusted for a sharp null at
center frequency with BRIDGE STABILITY ADJUST
A3R29. Actually, this control is set for a very slight
bridge unbalance to produce just enough positive feed¬
back so that signal current to the base of A3Q8 is
supplied mainly by A3Q7. Thus, at resonance, negligible
signal current flows through BANDWIDTH control, R3,
Model 415E
and gain is independent of its setting. Center frequency
is set by varying resistors R4 and R5 (these resistors
are ganged and comprise the front panel FREQ control).
4-16. FINAL AMPLIFIES.
4-17. The output amplifier consists of four transis¬
tors. The two output transistors, A3Q12 and A3Q13,
operate as a push-pull class B amplifier with both
collectors AC grounded. The emitters of these tran¬
sistors are tied together and the AC amplifier output
is taken from this point through a coupling capacitor,
A3C28. Large negative feedback makes the gain of
the output amplifier very nearly unity. The AC output
voltage is developed across resistor A3R51: The cur¬
rent through A3R51 is supplied by A3Q12 and A3Q13
conducting one at a time on alternate half cycles (Class
B operation ) and the output signal sine wave is
a composite of this half-cycle operation. In addition,
the collector current of A3Q13 can drive the meter
directly. No rectifier diodes are needed. This meter
driving current is filtered by capacitor A3C26 and
passes through the meter and a 1000 ohm resistor, R6,
to develop a DC voltage for the recorder output.
4-18. GROUND LOOPS.
4-19. The grounding technique used in the 415E con¬
sists of an input connector ground, a circuit board
ground, and output connector grounds. These are
"floating" grounds that are tied together and isolated
from chassis ground except for a 46. 4 ohm resistor,
R7, and a 0.05 uf capacitor, Cl, connecting ground
and chassis. A solid connection to chassis-or-earth
ground permits troublesome ground loop currents to
flow causing erroneous instrument operation. For
this reason, connecting grounded instruments to the
415E output connectors can cause erroneous readings.
Most recorders and oscilloscopes that might be used
with the 415E outputs have differential inputs available
with neither side grounded (see Paragraph 3-11).
4 - 20 . INPUT IMPEDANCE.
4-21. The Model 415E is designed to have an input
impedance much higher than that of any crystal detec¬
tor or bolometer normally used with it. This results
in lower noise figure and the highest possible input
signal to the 415E. For example with the 415E INPUT
switched to LOW, the input impedance is approximately
2000 ohms while the output or source impedance of a
bolometer is approximately 200 ohms.
4-2
02152-3