Tektronix 1L40, Instruction Manual

Page: 60 / 145

Performance C heck/Calibration— Type 1L40
First N inth
A . 1 m arker/centim e ter (1 0 % error)
First N inth
Centimeter
Line
irst
arker
Cent
Li
meter
ne
fc __
^ F
M
Fi Fth
M a rker '
B. 1 m a rk e r/2 centimeters (5 % error)
must remain within listed specifications given in Table 5-1,
to the -f- and —25 MHz positions.
g. Center the coarse IF CENTER FREQ control. Set the
DISPERSION control to .5 MHz position and apply 10 ns and
1 /is markers from the Time-Mark Generator.
h. CHECK— The range of the IF CENTER FREQ-FINE control.
Must equal or exceed -( -a n d — 1 MHz from its centered
position.
i. Return the VERTICAL DISPLAY switch to the LIN position.
TABLE 5-1
DISPER­
SION
Position
M a rke r
Selection
M a rk e rs /
Cm
A llo w ­
able
Error
S upplem entary
Notes
10 MHz 10 ns and
.1
/IS
i
3%
5 MHz 10 ns and
.1 /IS
1 marker/
2 cm
3%
Dispersion ac­
curacy must
hold over the
range of the IF
CENTER FREQ
2 MHz 10 ns and
.5 /is
1 5%
1 MHz 10 ns and
1 /IS
1
7%
control
( ± 2 5 MHz).
.5 MHz 10 ns and
1 /is
1 marker/
2 cm
10%
Display linear­
ity over a 10
centimeter dis-
.2 MHz 10 ns and
5 /is
1 15% play must be
within 3%.
Fig. 5-3. Typical dispersion accuracy displays (step 2 ) .
f. Check the range of the IF CENTER FREQ control plus the
dispersion accuracy and linearity over this range, in the 5, 2,
1, .5 and .2 MHz positions of the DISPERSION selector.
Range of the IF CENTER FREQ control should equal or ex­
ceed - f and — 25 MHz from its centered position. Rotate the
control from center and note the frequency shift of the .1 /is
or 10 MHz markers, then rotate the control to the other
extreme position. Dispersion accuracy and display linearity
This m arker This marker
on graticule X cm on graticule
Percent n o n lin e a rity = —-------- X 100
8 cm
Fig. 5 -4 . M easuring displersion lin e a rity.
2(B) Adjust Frequency Dispersion and O
Linearity
When making a Performance Check only, omit this step and
proceed to step 3 (A).
Dispersion accuracy and the display linearity for the Type
1L40 is a function of the RF output amplitude, circuit con­
stants, etc. DISP CAL adjustment R208, primarily affects the
dispersion accuracy and C358 (lO M H z/C M Linearity) the
linearity. If these two adjustment w ill not calibrate the dis­
persion to specifications the following techniques may be
tried.
Shift the sweep oscillator RF output voltage to a new
level. (Output voltage level must remain within — 0.7 and
— 1.0 volt.) If the level is changed, the Center Freq Range
adjustment (step 1) must be repeated.
Interchange Q310, Q340 and Q350. The slight differences
between the transistor parameters w ill have some effect on
display linearity.
Interchanging the discriminator cables
(W375 and W370) with another length is also a possible
correction.
Changing these transistors or cables is only
recommended after new transistors have been installed or
components have been changed and linearity cannot be
obtained by other means.
a. The equipment setup for this step is shown in Fig. 5-1.
b. A pply .1 /.is and 10 ns markers from the Time-Mark
Generator (Type 184) through a 20 dB attenuator a 50
Cl
termination and the proper adapter to the RF INPUT connec­
tor. Set the VERTICAL DISPLAY switch to LOG position.
5-6