ADJUSTMENTS

5-19. LOG AMPLIFIER LOG AND LINEAR ADJUSTMENT(SERIAL PREFIX 22O8A) (Cont'd)

12.Set step attenuator to 0 dB. Digital voltmeter should indicate 800 mV, plus offset (algebraicsum) *1 mV. If DVM reading is not within limits, adjust A14R2 LOG LIN adjustment for a digital voltmeter reading of 800 mV, plus offset minus 50 percent of overshoot. (Example: if DVM indicates 767 mV and should be indicating 777 mV (- 10 mV overshoot), adjust A14R2 for a DVM reading of 777 mV minus -5 mV, or 782 m l )

13.Repeat steps 10, 11, and 12 until the digital voltmeter indicates800 mV plus offset f1 mV with no further adjustment of Al4R2 in step 12.

14.Set the step attenuator to the positions shown in Table 5-7 and record DVM reading for each setting. Correct the DVM readings by algebraically adding the offset (recorded in step 9).

 

 

 

 

TABLE 5-7. LOG FIDELITY CHECK

 

 

 

 

 

 

 

 

 

 

DVM Reading Corrected for

 

 

 

Step Attenuator

 

 

DVM Reading

 

1

 

 

 

 

 

Setting (dB)

 

 

(mV)

 

 

Min. (mV)

Actual (mV)

Max. (mV)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

15.Readjust A14R2if necessary to meet the limits in Table 5-7.

16.Set step attenuator to 0 dB and set output level of signal generator for a digital voltmeter reading of 800 mV plus offset (recorded in step 9) f1 mV.

17.Set Amplitude Scale to LIN. The digital voltmeter should indicate the reading set in step 16 *25 mV. If it does, go to step 19. If it does not, or if log fidelity is not within limits, go to step 18 and select A14R16*.

18.Select A14R16* to obtain an output in step 17 within f25 mV of the reading set in step 16. Decreasing A14R16* 10 percent will increase the DVM reading approximately 30 mV in step 17.

NOTE

Log fidelity must be considered when selecting A14R16*. That is, if the DVM READING CORRECTED FOR OFFSET in Table 5-7 is greater than 100 mV for a STEP ATTENUATOR SETTING of 70 dB, A14R16* should be selected for a DVM reading greater than the reading set in step 16. If the READING CORRECTED FOR OFFSET is less than 100 mV, A14R16* should be selected for DVM reading less than the reading set in step 16.