Dynascan B&K 2050 User manual

INSTRUCTION
MANUAL
.
..
..-
(
RF SIGNAL
GENERATOR

Dear Friend:
Congrat ula ti ons on your purchase of B& K-Precision
T st Equipment, and welcome to the B & K family. We
hop e yo ur experie nce with your new test equipment
will ma ke y ou a lifet ime B & K customer.
Your ins tru men t is bac ked by more than 20 years of
experience in d esign ing and manufacturing. Our most
important g oa l is your sa tisfaction. At B & K, test
equipmen t is mad e to me et th e demands of th e field focus ing on de p endability
and acc ur acy. We al so conc entra te on si mp lici ty an d operati n ease with
features th at red u ce the possibility of hum an error a nd speed the servicing
proc ess .
In order to de termine th e typ e of t es t units t ha t are needed we have been
guided by lett ers an d reports from t ec h nicians and engineers w ho us the
equ i pmen t da ily. Ou r fi e ld t es ts and stu dies ha ve helped pr ovide bette r and
fast er serv ice tec hniqu es. Cl ose co nt ac t h as been m ai nt ai ned with t he m anu-
fac t urers of cons um er pro d ucts which our test un its will be ch ec king and
troub le-shooting.
K ey p erso nne l in our co mp any cu t their eye t ee th in the TV service b usin ess .
This is why we hav e more "sensitivity" for th e pr o bl em s and conditions under
which the tes t e qu i pmen t will be us ed .
B & K product designs are constan tly reviewed, a nd refinemen ts ar e made
or n w models devel o ped to meet ad v ances in o ur in dus try a nd to fill your
n ee ds . W se t our s tan dards hig h so you can be a ured t hat the B & K test
instrum e nts you buy r epresent ad van ce d desi gn , qua lity co n struc tion, and
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in general, I would be delig ht ed to h ea r fr om y ou .
Tha nks for your confiden ce in B & K and we look forwar d to se rving you for
a l ong t ime to come.
Sincerely,
Cl-/~
Carl Korn
President

INSTRUCTION MANUAL
FOR
Model 2050
RF SIGNAL
GENERATOR

TABLE OF CONTENTS
Features .................................................. .- .. 2
Specifications
................................................. 3
Theory
of Operation ............................................ .4
Operator's Controls and Panel Indicators ................................ 5
Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Applications
.................................................. 8
Maintenance
................................................. 11
Adjustments ................................................. 13
Precautions .................................................. 15
Block Diagram (Fig. 1) .......................................... 15
External View of the 2050 .... - ................ , ..................... 16
Warranty Service Instructions
................................... Cov. 3
Warranty
................................................ Cov. 3
FEATURES
• All solid-state construction.
• Compact, easy-to-read frequency scale with smooth mechanism.
• 100 kHz to 30
MHz frequency coverage in 6 ranges, each in different
color on dial for quick, accurate readings.
• Output voltage
of better than 0.1 V rms, continuously variable to any
desired magnitude through combined use of 20
dB (approximately 1/10)
attenuator and RF OUTPUT control.
• Modulation
is either internal (approximately 40% at 400 Hz) or external
(SO Hz to 10 kHz)-selectable by MODULATION switch.
• High stability against supply voltage fluctuations.
• Convenient markings on dial plate for making adjustments and frequency
checks in Amateur band, TV and
AM receivers.
2
•

Frequency Ranges
Frequency Accuracy
Output Voltage
Attenuator
Internal modulation frequency
Internal modulation level
External modulation frequency
External modulation voltage
Operating temperature
Power requirements
Power consumption
Dimensions overall
Weight
Accessories
MODEL 2050
SPECIFICATIONS
Band
Frequency
A 100 kHz to 250 kHz
B 250 kHz
to 650 kHz
C 550 kHz
to 1.5 MHz
D 1.5
MHz to 4 MHz
E 4 MHz to 11 MHz
F 10MHz to 30MHz
±1.5%
0.1 V rms or better (20 • C.)
HIGH-LOW (provides approximately 20 dB change)
Approximately
400 Hz
40%,±5%
50 Hz to 10 kHz
1.5V rms for 40% modulation
0
to so· C.
100V, 117V or 230V AC, +10%, 50/60 Hz (unit
supplied for use on 117 V AC, 50/60 Hz line)
2.8 watts
71h x 9-3/4 x 6-1/8 inches
5 lb.
Shielded lead with insulated clip and banana plug;
fuse; instruction manual.
3

THEORY OF OPERATION
1. Outline. Please refer to the block diagram of Fig. 1 (P. 15).
The sine
wave signal produced in the RF oscillator circuit is directly amplified by
the modulated amplifier when the MODULATION switch
is at CW, then passes the
output attenuator, and appears at the output terminal. When the MODULATION
switch
is set to INT, the output can be internally modulated to approximately 40%
at 400 Hz by sine wave signal from the AF oscillator circuit, or externally
modulated when the switch
is shifted to EXT. Required level of the modulating
signal
is more than 1.5V rms for 40% modulation at frequencies between 50 Hz and
10 kHz.
2.
RF Oscillator Circuit. The RF oscillator circuit employs a Hartley circuit, the
oscillating elements consisting
of coils (FREQ. RANGE), which are switched in six
ranges, and a variable capacitor (FREQUENCY dial), covering 2.5 times the lower
edge
of each range or a total range of 100 kHz to 30 MHz.
The amplifier circuit for the oscillator is a high input impedance circuit employ-
ing an FET and includes a feedback resistor for each range
so that output may be
equal in all ranges.
3. Modulated Amplifier. The signal from the RF oscillator circuit is amplified by
Q2, passes the modulated amplifier (a gate-modulated type built around Q3), and
then an
RLC type low-pass filter before being taken out through an emitter
follower, Q4.
4. AF Oscillator Circuit. Transistor Q5 forms an LC oscillator circuit, and its output
is couple.d to the modulated amplifier through VRl (INT. MOD. ADJ.).
5. Power Supply. Input AC voltage (100V, 117V or 230V AC) is stepped down to
a required voltage by the power transformer, rectified (full-wave) by rectifier D1,
and passed through a smoothing circuit to obtain the
DC voltage. This power supply
section feeds 15V
DC to all signal generator circuits as "B" voltage.
4

OPERATOR'S
CONTROLS AND PANEL INDICATORS
NOTE: This instrument is supplied for use on 117 V AC, 50/60 Hz lines. For 100 V
AC or 230 V AC operation, please refer to the instructions under "PRECAUTIONS,"
on page 15
of this manual.
The 2050's controls and their functions are
as follows (refer to EXTERNAL VIEW
drawing on page 16):
FRONT PANEL
Ref. Controls, Description
No. Connectors, etc.
( 1 ) (Neon lamp) Lights up when POWER switch (2)
is
turned to ON.
(
2) POWER Slide switch; turns power
ON when set
to right-hand position.
(
3) MODULATION Selector switch for modulating signal.
EXT In this mode,
output signal can be
AM-modulated at any frequency be-
tween 50
Hz and 10 kHz when a
modulating signal
is fed to EXT MOD
INPUT terminals (12) and (13).
cw
This is the central position of the
MODULATION switch, and produces
unmodulated output.
INT Output
is AM-modulated by the built-
in AF oscillator to approximately 40%
at
400 Hz.
(4)
~ (GND) Grounding terminal.
(
5)
RF OUT Any
output can be obtained from this
output terminal.
( 6)
OUTPUT Output attenuator .
=20 dB
HIGH In this position,
output is applied
directly to the
output terminal with-
out attenuation.
LOW
Gives an attenuation of approximately
20 dB.
5

Ref. Controls, Description
No. Connectors, etc.
(7)
RF OUTPUT Permits changing
output voltage con-
tinuously between Oand 0.1 V rms.
(8)
FREQ.RANGE Used to select frequency ranges indi-
cated on scale (10) and pointer (11)
as
follows:
A:
100 kHz to 250 kHz
B: 250 kHz to 650 kHz
C: 550 kHz to 1
.5 MHz
D:
1 .5 MHz to 4MHz
E: 4
MHz to 11 MHz
F: 10
MHz to 30 MHz
(9)
(Frequency d1a l) Used to select desired
output fre-
quency. Mechanically ganged with the
variable capacitor and pointer (
11 ).
(10 ) (Scale plate) Graduated in six ranges
to read output
frequencies between 100 kHz and 30
MHz.
(1 1) (Pointer) Indicates scale settings.
REAR PANEL
(12) EXT
MOD INPUT Input terminal for external modul
a-
tion signals. To modulate the 2050
with an external modulation signal,
feed a signal to this terminal and set
MODULATION switch
(3) to EXT.
Usable modulating frequencies are be-
tween 50
Hz and 10 kHz.
(13) GND
Grounding
terminal for external
modulation.
(14) (Power cord} Power supply cord.
6

OPERATING INSTRUCTIONS
1. Preliminary Setup. With power cord (14) connected to a power source, turn power
switch (2)
to ON. This turns neon lamp (1) on and places the signal generator in the
operating condition. Allow 2 or 3 minutes warm-up for optimum frequency stability.
2. Selecting a Specific Frequency. To set
to a specific frequency, select a proper range
with FREQ. RANGE switch (8) and operate FREQUENCY dial (9) until its pointer (11)
indicates the desired frequency
on scale (10). The frequency dial is ganged with the
variable capacitor.
For example,
to set to 1 MHz:
Set FREQ. RANGE switch (8) to C, and pointer (11) to 1 MHz on scale (10).
3. Adjusting Output Voltage. Output voltage at output terminal (5) can be continuously
adjusted from O
to 0.1 V rms by means of RF OUTPUT control (7). The RF OUTPUT
control increases the output voltage when turned clockwise, up
to O.lV rms at the fully
clockwise position if
output attenuator (6) is at HIGH. When the attenuator is set to
LOW, the output voltage is reduced to approximately 1/10 (-20 dB). When obtaining a
small voltage, set the attenuator to
LOW, since this makes adjustments easier at such
small voltages.
4. Using the EXT
MOD INPUT Terminal (Rear Panel). When connected to an external
sine
wave signal, this terminal enables the output voltage to be AM-modulated at a desired
frequency between 50
Hz and 10 kHz, when the MODULATION switch (3) is at EXT.
Required modulating voltage
is approximately 1.SV rms for 40% modulation.
7

APPLICATIONS
The standard radio intermediate frequencies are as follows:
AM Broadcast IF
AM Broadcast IF,
FM Broadcast IF
455 kHz
262 kHz
10.7
MHz
In the applications of the 2050 described below, it is assumed that the broadcast
receiver IF
is 455 kHz, and the FM IF is 10.7 MHz.
Following are examples of how to use the B & K 2050 to check the frequency
response
of RF and IF amplifiers of AM receivers:
1. Aligning IF Transformers. Set the 2050 to 455 kHz, the intermediate frequency of
the AM receiver to be aligned, and connect the 2050 to the base of Transistor Tr2, a•
mixer (See Fig. 2). The local oscillator must be kept inoperative during this adjustmen·t.
To make it inoperative, shunt the base of the local oscillator transistor or the tank circuit
to ground.
Connect an output meter (or a
VOM set to 2.5-lOV DC range) to the emitter of Tr3,
and measure the emitter voltage. This voltage, which
is high when IFTl is detuned, will
drop
as IFTl is tuned to 455 kHz. IFT1 now is accurately tuned. Next, gradually change
the frequency
of the 2050 output to points above and below the 455 kHz point, to
obtain a curve, as shown in Fig. 3. A detuning width between points that yield 3 dB
difference in output as compared to the center frequency, is the passband of the IF
transformer; the attenuation obtained when the IF transformer is detuned ±-10 kHz from
the center frequency,
is the rated selectivity.
ANT. Trl
~!![!
~~
o=c
OUT
Tr2
Local OSC
8
Tr3
Volt meter
(VOM)
Tr4
FIG2. ALIGNING IF AMPLIFIER