Leader Electronics Corp. LSG-17 User manual

"TECHNICAL FILE"
. .
MODEL LSG-17
WIDE BAND SIGNAL GENERATOR
lNSTRUCTION MANUAL.
LEADER ELECTRONICS CORP.

Model LSG-17
SIGNAL GENERATOR
TABLE OF CONTENTS
SECTION PAGE
General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1
SPECIFICATIONS......................... 1
2DESCRIPTION 2
2.1 Controls 2
2.2 Circuit
Design. . . . . . . . . . . . . . . . . . . . . . . . . 3
3OPERATION 5
3.1 Preparation 5
3.2 .Connections 5
3.3 Modulated Carrier, internal source. . . . . . . . . . . 6
3.4 Modulated Carrier, external
source. .......... 6
3.5 Unmodulated Carrier 6
3.6 Crystal Oscillator
Output . . . . . . . . . . . . . . . . . 7
3.7 AF
Output, 1kHz 7
3.8 Oscillator Frequency Calibration 8
3.9 Removal
of Chassis from Cabinet 9
3.10 The Line Voltage Changing. . . . . . . . . . . . . 9
Block Diagram
Schematic

General
LSG-17 is avery versatile thick film integrated circuit (IC), wide-
band signal generator designed for the radio experimenter, hobbyist,
service technician and instructional purposes. An IC
is used in astable
oscillator circuit
to cover the frequency range from 100kHz to 150MHz
on fundamentals and up to 450MHz on harmonics. Among the many
features are
the large easy-to-read dial marked at 455kHz and
10.7MHz, one audio frequency for amplitude modulation
or external
use, provision for crystal oscillator operation. Serves
as amarker
generator when used with asweep generator in checking and aligning
RF and IF circuits in TV and FM receivers.
SECTION 1
SPECIFICATIONS
Frequency Range
Band
Frequency Accuracy
RF Output
Output Control
Modulation
100kHz
to 150MHz (up to 450MHz on
harmonics)
A100 -300kHz
B
300 1000kHz
C1.00 -3.5MHz
D3.0
-l1MHz
E10 -35MHz
F
32 -- 150MHz (96 450MHz,
calibrated harmonics)
±1.5%
100mVrms, approx.,
up to 35MHz. (open
circuit)
HIGH-LOW switch and flne adjuster.
Int.: approx. 1kHz 30% ±10%
Ext.: 50Hz-20kHz, at less than .15Vrms
(30% ±5%) input.
-1-

Audio Output
Cyrstal Oscillator
Power Supply
Size and Weight
1kHz; 1Vrms or more (fixed).
For l-l5 MHz crystal in Type FT-243
holder. (not included).
100, 115 120, 220 -240V, 50/60Hz;
approx.3VA.
l50(H) X238(W) X80(D) mm; 2.5kg.
SECTION 2
DESCRIPTION
®
2.1 Controls
Frequency dial Sets the RF output frequency in
the range selected with FREQ
RANGE switch.
FREQ RANGE switch With six positions for RF output
frequency range.
- 2 -

INPUT-OUTPUT
XTAL socket
POWER switch
Pilot lamp
Mode switch
For insertion of quartz crystal,
1-15MHz, in Type FT-243 holder.
For turning on the AC power.
Indicates when AC power
is on.
EXT
MOD: For modulation of
carrier with an external source.
INT
MOD: Use of internal 1kHz
for modulation or external cir-
cuit testing.
XTAL OSC: Crystal oscillator out-
put; frequency depends on crys-
tal used.
For external modulation .input or
output from internal 1kHz oscilla-
tor.
@FINE control Continuous RF output voltage ad-
juster.
RF LOW-HIGH switch Sets the RF output level; at LOW,
output is lowered by 1/10.
OUTPUT terminals For connection to RF output leads.
2.2 Circuit Design
The circuits which compose the LSG-17 will be described
with reference to the functional block diagram and components
designated
on the schematic.
A. RF Circuit.
The
RF oscillator uses an IC, IC102, in the Colpitts
circuit to generate frequencies from 100kHz
to 150MHz
on fundamentals. The frequency of operation is set with
the FREQ RANGE switch and the tuning dial. Calibration
-3-

accuracy is better than ±l.5%. For convenience in setting
the IF circuit frequencies, tuning scales are marked at
455kHz and 10 .7MHz.
The RF output is controlled with the fine adjuster
and LOW-HIGH switch.
For amplitude modulation, the audio signal is sup-
plied
by the modulator, IC101. The modulating is done
by varying the supply voltage at the audio rate.
B. AF Oscillator/Amplifier and Crystal Oscillator.
An IC, IC101 is used for three functions, depending
on the positions of the mode switch.
At EXT MOD position, it serves as an audio amplifier
for
the external modulation input. The signal from INPUT
is applied to the IC101 and on to the modulator.
The 1kHz signal is generated with use of the phase-
shift oscillator.
The output is fed to the modulator and
OUTPUT (when used externally).
At XTAL position, IC101 acts as an oscillator when
acrystal,
1-l5MHz, is inserted in the XTAL socket.
The output is connected to the LOW terminal of LOW-
HIGH output switch. The signal is available at the OUT-
PUT
connector at the LOW position. It is possible to super-
impose the
RF oscillator signal on the crystal oscillator
output at this position.
C. Power Supply.
ADC voltage
is supplied from arectifier-ftlter system.
Unregulated voltage at approximately
+20V is used for
the IC101 and IC102 circuits. IC101 includes regulated DC
power supply. Regulated DC is supplied
to the IC101 and
IC102.
4

The power transformer T1 01, has its primarywindings
with three taps;100V, 115-120V, 220-240V. It is easy
to change line voltage.
The LED,
D103 is connected across the +20V power
supply through
the RI09.
SECTION 3
OPERATION
3.1 Preparation
(1) Set the POWER switch at OFF.
(2) Connect the AC plug
to the AC supply.
(3) Connect the
RF output leads to OUTPUT terminals.
(4) Set the FINE control at center and the
RF slide switch
at
LOW.
During the tests, this switch is set· at LOW or HIGH as
required.
(5) Set the
FREQ RANGE switch at the operating band and
rotate the frequency dial knob
to set the pointer on the
desired frequency.
3.2 Connections
The
RF leads are connected to the input of the circuit
under test. The red terminal is at high potential, or
"hot", and
black is
at ground potential for chassis connection.
For the
RF signal at the receiver antenna input, connect
a50
to 200 ohm resistor, 1/4W, in series. When checking sets with
the bar
or rod antenna, connect leads to acoil with afew turns
of wire and couple the coil to the antenna.
In checking
RF and IF amplifier circuits, connection
should be made through asmall capacitor,
1-5pF, in order to
-5-

prevent detuning effects.
NOTE: When connecting directly
to the input circuit, make
certain
that there is no ,high DC voltage present.
Otherwise, connect ablocking capacitor,
0.05 uF -100
pF, depending on the frequency.
3.3 Modulated Carrier, internal source
Set the mode switch at INT. MOD.
By tuning the receiver to the generator frequency, or vice
versa, an audio
tone will be heard in the loudspeaker. An audio
voltmeter should be connected across the speaker terminals when
aligning the internal circuits. A
dummy resistor with suitable
power rating can
be used in place of the moving coil curing
the measurements.
It is advisable to keep the RF signal level as low as possible
in order
to prevent overloading the transistors or IC in the circuit.
Excessive
input voltage will cause AGC action and/or two
resonance points
to appear and proper alignment or adjustment is
impossible.
3.4 Modulated Carrier, external source
Set the mode switch at EXT, MOD.
Connect leads from an external audio generator
to the
INPUT.
Frequencies
up to 20kHz can be used for modulation.
The audio input voltage should not exceed 0.5V; this is to pre-
vent modulation distortion.
3.5 Unmodulated Carrier
Set the mode switch at EXT. MOD. There should be no
connection
to the INPUT.
6

The RF signal can be used in testing areceiver equipped
with a
beat oscillator, or circuits that do not require amodulated
signal.
The
RF signal can be applied to asweep generator for the
marker signal.
3.6 Crystal Oscillator
Output
Control settings:
Mode switch
at XTAL. Insert acrystal, in FT-243 holder,
in the XTAL socket.
RF output switch at LOW.
FREQ RANGE switch at "F" and frequency dial at
150MHz.
FINE control
at minimum.
The
output signal is treated in the same manner as for
the unmodulated carrier with the exception that the output
level cannot be adjusted.
In certain calibration procedures ashort lead near
the
test circuit will provide sufficient coupling.
NOTE:
If the RF signal is required at the same time, set
the
output frequency with the FREQ RANGE switch
and frequency dial
as required. Adjust the RF FINE
control.
3.7
AF Output, 1kHz
Control settings:
Mode switch at INT. MOD.
FREQ RANGE switch at "F" and frequency dial at
150MHz.
Connect leads from OUTPUT to the test circuit. Use
an external potentiometer, 100k-1M, to lower the voltage.
- 7

3.8 Oscillator Frequency Calibration
The RF oscillator frequency can be calibrated to ahigh
degree
of precision using the harmonics of the internal crystal
oscillator
and an external all-wave receiver. The latter is utilized
as afrequency transfer unit. I
(1) Set the mode switch at XTAL.
(2) Insert the "standard frequency" crystal, preferably at
amultiple of 1MHz. For spot frequency checking, at say
10.7MHz, use a10.7MHz crystal.
(3)
Set the RF slide switch at LOW.
Adjust the FINE control as required.
(4)
Connect the RF output to the receiver input, direct or
through asmall coupling capacitor to the rod antenna.
(5) In
the following example, use of a1MHz crystal will be
given.
(6) Tune
the receiver to 5MHz, or 5th harmonic of IMHz.
Then by carefully tuning
both the oscillator and receiver,
an audio
beat will be heard. The oscillator is adjusted to
zero beat and the dial reading is noted. At other frequen-
cies spaced 1MHz apart, the same procedure
is repeated,
namely, oscillator setting tuning the receiver retuning
oscillator and noting the reading on the dial.
Practical use
of harmonics up to the tenth or higher is
possible. However, care must be exercised in selecting
the proper harmonic, especially at high RF when arela-
tively low frequency crystal
is used.
NOTE: When areceiver equipped with a
beat frequency
oscillator
is used, the measurements can be sim-
plified. The
"zero-beat" condition is at the point
where the steady
beat is heard most clearly.
8

3.9 Exposing the chassis
The chassis can be exposed in the following manner for
inspection:
(1) Loosen one screw
at front part of top cover.
(2) Remove one screw on the bottom side.
(3) Remove one screw at the back.
(4) Take off the cover.
3.10 The Line Voltage Changing
This instrument can be oper-
ated from AC line sources of 100V,
115V -120V or 220V -240V.
The Line Voltage Selector
(pin
connector with plastic cover)
allows one
of three voltages to be
selected.
Fig. 3-1
115~
120V lOOV
9

To select the desired line
voltage, proceed
as follows:
(1) DISCONNECTTHE INSTRU-
MENT FROM THE POWER
SOURCE,
(2) Remove screw on the right
side of
the instrument then
take the cover off. (Ref:
Fig. 3-1)
(3) Move
the Line Voltage Se-
lector to the desired voltage
position. (Ref: Fig. 3-3)
LINE VOLTAGE SELECTOR
Fig. 3-2
Block diagram
AF
IN/OUT
IC 102
OUT ONLY
SIG SELECT
I C101
XTAL.