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6. Video Processor
Adjustments
Reference
Related Performance
Description
Equipment
Note
Procedure
IF-Display Section
Log Scale Switching Uncertainty Test
The CAL OUTPUT signal is connected to the RF INPUT through a
step attenuator. The instrument is placed in zero frequency span to
produce a dc level output from the log amplifier. The A4A2 ZERO
adjustment, which sets the dc offset of the output buffer amplifier of
the log board, is checked and adjusted if necessary. The dc level into
the video processor is adjusted by varying the input signal level and
reference level. The offsets and gains
are adjusted for proper levels using a DVM.
Figure 3-35. Video Processor Adjustments Setup
Digital Voltmeter (DVM) . . . . . . . . . . . . . . . . . . . . . . . . HP 3456A
10 dB Step Attenuator . . . . . . . . . . . . . . . . . . . . . . . . . . HP 355D
The voltage at A4AlTP3 may drift noticeably with temperature
during this adjustment. Allow A4Al (Video Processor) to warm up at
least one-half hour prior to adjustment.
1.
Position instrument upright as shown in Figure 3-35. Remove the
top cover.
2.
Set LINE switch to ON and press
3.
Connect DVM to A4AlTPl and DVM ground to the IF casting.
Connect CAL OUTPUT to RF INPUT through 10 dB step
4.
attenuator.
Key in
5.
[
CENTER FREQUENCY
Press LIN pushbutton.
6. Video Processor Adjustments
the A4Al Video Processor
on
D I G I T A L
V O L T M T E R
).
PRESET
20 MHz and
)
[
FREQUENCY SPAN
0 Hz.
)
Adjustments 3-69
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