Section N Model 240A
Paragraphs 4-34 to 4-42
J402
multi-vibrator oscillator V501 by means of the
ganged potentiometers R529A and R529B labeled
SWEEP RATE. In the LINE SYNC position, voltage
of the power source frequency is applied to one
(I grid, pin 7, of the V501 multi-vibrator.
RF LEVEL I
VERNIER I ,
4-38. Either the output of the multi-vibrator OS-
cillator or an external sweep voltage applied through
IO STEP ATTENUATOR the EXTERNAL SWEEP IN post 5501, is fed to the
grid of amplifier V502. The time constants in this
1 circuit are chosen so as to integrate the rectangular
' TO
METER waveform from the multi-vibrator into a triangular
saw-tooth waveform. This waveform, or the EXTER-
Figure 44. Output Attenuator System
NAL SWEEP waveform, is amplified in the second
half of V602 and delivered as EXTERNAL SWEEP
OUT voltage through the front panel post 5503.
4-34. The output of the "L" pad is fed to a 10-step
attenuator unit AT401, having 10 db per step. The
4-39. The SWEEP WIDTH control, R536, feeds a
output impedance of the step attenuator is 50 ohms
controllable amount of saw-tooth voltage into the
resistive except on th3 maximum output position in
amplifier V504 whose output appears across the
which case the impedance rises somewhat. The out-
cathode load resistor, R542, of the second section,
put of the attenuator is connected with the front panel
which is common with the dc amplifier, V505.
RF OUTPUT jack, 5402, by a 50-ohm coaxial cable.
4-35. The equivalent voltage source of the output VOLTAGE
system is shown in the diagrams of Figure 4-5. For PIN l* V504, TO
GROUND
50 ohms impedance, add an external 25-ohm resis-
tor.
VOLTA G E
PIN 1, V505, TO
TYPE 240-A GROUND
r-------
VOLTAGE
PIN 5* RF TERM.
BOARD.10 GROUND
I J-402 I
-
I ATTENUATOR READS~*E*I/
Figure 4-6. Sweep Control Waveforms
A. OPEN CIRCUIT AT PANEL JACK
TYPE 240-A
r--=--- 1 I
4-40. SHAPING CIRCUITS.
I 4-41. For the reasons mentioned in paragraph
I <-
4-26, it is necessary to adjust the waveshape of the
' I a m U P saw-tooth current being fed to the yokes, LA08 and
'U I 50 SL LA09, in order to produce a linear deviation of fre-
ATTENUATOR READS'*E'~
L-, - - - - quency as a function of the original saw-tooth tolt-
0. ACTUAL CIRCUIT WITH CABLE
age. This is done by the voltage shaping network in
the grid and cathode of V505; the triple diode, V506;
and the compensating resistors associated with
RF LEVEL S501, sections D, E, and F. The bias voltages ap-
METER pearing across the three elements contained in the
READS 6BJ7 tube, V506, are controlled by the five poten-
*. E " tiometers R549, R553, R558, R564 and R573,
which are selected by the frequency range switch.
C . EQUIVALENT CIRCUIT THRU CABLE
442. These bias levels determine when each diode
Figure 4-5. RF Output Characteristics cuts into the circuit as the dc voltage 011 the cathode
increases. The amount by which each diode changes
the slope of the waveform is determined by the addi-
tion of the resistances R548, R552, R557, R563 and
4-36. SWEEP GENERATOR.
R568 in the voltage divider containing R539 from the
4-37. The repetition rate of the sweep voltage ap- cathode of V504. Additional control is obtained
plied to the saturable reactor is controlled in the through the diode CR501 acting on the cathode of V505
4-4 |
ACEC
HEWLETT-PACKARD
