HP 8568B manual VTV and Atten Adjustments, Linear Gain Adjustments

5. Log Amplifier Adjustments

Bandpass Filter Amplitude Adjustment

9.Connect one end of a jumper wire to A4A3TP8. Connect the other end of the jumper to A4A3TP7 (+ 15V). Connecting the jumper to A4A3TP8 first reduces the chance of shorting the + 15V to ground. Note DVM indication.

V dc

10.Remove the short from between A4A3TP7 and A4A3TP8.

11.Adjust A4A3R67 AMPTD for DVM indication the same as that noted in step 9 f0.0005 V dc. See Figure 3-34 for location of adjustment. If unable to adjust A4A3R67 AMPTD for proper indication, increase or decrease value of A4A3R66. (If A4A3R67 is fully counter-clockwise, increase the value of A4A3R66.)

Refer to Table 3-3 for range of values.

12.Repeat steps 9 through 11 until DVM indication is the same f0.0005 V dc with A4A3TP7 jumpered to A4A3TP8, and with A4A3TP7 and A4A3TP8 not jumpered. Remove the jumper.

-12 VTV and ATTEN Adjustments

13.Press LIN pushbutton.

14.Adjust frequency synthesizer output level for DVM indication of

+1.000 &IO.0002 V dc.

Synthesizer level: dBm

15.Press LOG [ENTER dB/DIV)

16.Wait three minutes for the log assemblies to stabilize.

17.Decrease the frequency synthesizer output level by 50 dB.

18.Adjust A4A2R91 - 12 VTV for DVM indication of + 500 f 1 mV dc. See Figure 3-34 for location of adjustment.

19.Increase the frequency synthesizer output level by 50 dB (to the level of step 14).

20.Adjust A4A2R61 ATTEN for DVM indication of + 1.000 *O.OOOl V dc. See Figure 3-34 for location of adjustment. If unable to adjust A4A2R61 ATTEN for proper indication, increase or decrease value of A4A2R62. (If A4A2R61 is fully clockwise, increase the value of A4A2R62.) Refer to ‘Ihble 3-3 for range of values.

21.Repeat steps 17 through 20, until specifications of steps 18 and 20 are achieved without further adjustment. Because adjustments A4A2R61 and A4A2R91 are interactive, several iterations are needed.

Linear Gain Adjustments

22.Press LIN pushbutton. DVM indication at A4AlTPl should be

+1.000 f0.020 V dc (+ 0.980 to + 1.020 V dc). If indication is not within this range, repeat steps 14 through 21. If indication is within this range, press [*I CENTER dB/div] q. This disables the IF step gains.

Adjustments 3-67