Tektronix 1L40, Instruction Manual

Page: 14 / 145

Operating Instructions— Type 1L40
(A ) Large and small beat signal displays. LOCK CHECK
bu tton is depressed w h ile the RF CENTER FREQUENCY con­
tro l is slow ly tuned.
(B) LOCK CHECK button depressed w h ile RF FINE FREQ
control is adjusted. D isplay DC level w ill s h ift as control is
adjusted. Select a be a t mode near the screen center fo r best
op eration.
Signal feet
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1 thro jg h
n
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(C) N ull po in t. O scillator w ill now lock in phase w ith the ID ) LOCK CHECK b u tton released. N orm al d isp la y o f a phase
reference frequency. Release LOCK CHECK button. locked condition. Center desired signa l on screen w ith the IF
CENTER FREQ controls.
Fig. 2 -6 . Lock check displays
13. Set the DISPERSION selector to 500 kHz, switch the
DISPERSION RANGE switch to the kHz/CM position, then
decrease the DISPERSION to kHz/cm keeping the signal
centered on screen with the IF CENTER FREQ control. Un­
couple the RESOLUTION control and turn clockwise. Note
that the displayed bandwidth increases as the resolution
bandwidth is increased. The resolution bandwidth may be
varied from approximately 1 kHz to 100 kHz. Return the
RESOLUTION control to the coupled position with the DIS­
PERSION selector.
14. Turn the INT REF FREQ switch to the INT position.
15. Push the LOCK CHECK button and turn the RF CENTER
FREQ control slowly through the signal frequency. Note
the phase lock beat signals between the tunable local oscil­
lator and the Internal Reference Frequency oscillator as
the display blooms then snaps into the phase lock opera­
tion (Fig. 2-6). See Phase Lock Operation on page 2.
16. W ith the LOCK CHECK button depressed, adjust the
FINE RF CENTER FREQ control. Note the beat frequency
display, as the control is varied, and the vertical displace­
ment of the display baseline. This baseline vertical shift
is the change in the output DC level of the phase lock am pli­
fier. Note the zero beat signal compression at the extreme
position of this control compared to the amplitude near
the center. Phase lock condition should be set with the DC
level midrange between the two extreme positions noted
above on the CRT as the FINE IF CENTER FREQ control was
rotated. Adjust for phase lock operation and release the
LOCK CHECK button.
17. Set the DISPERSION selector to 500 kHz, switch the
DISPERSION RANGE switch to the kHz/CM position, then de­
crease the DISPERSION to 50 kHz/cm, keeping the signal
centered on screen with the IF CENTER FREQ control. If the
signal should suddenly shift off screen, phase lock operation
has probably been lost. A slight adjustment of the FINE RF
CENTER FREQ control w ill usually restore the phase lock con­
dition and return the signal on screen.
2-8