6.Video Processor Adjustments

Reference

Related Performance Test

Description

6. Video Processor Adjustments

IF-Display Section

A4A 1 Video Processor

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 on the A4Al Video Processor are adjusted for proper levels using a DVM.

Equipment

Note

Procedure

D I G I T A L V O L T M T E R

0 cd

1OdB S T E P A T T E N U A T O R

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 (INSTR PRESET).

3.Connect DVM to A4AlTPl and DVM ground to the IF casting.

4.Connect CAL OUTPUT to RF INPUT through 10 dB step attenuator.

5.Key in [CENTER FREQUENCY) 20 MHz and [FREQUENCY SPAN) 0 Hz.

Press LIN pushbutton.

Adjustments 3-69