HP TM 11-6625-2779-14&P Frequency Response Adjustment, Common Mode Adjustment, Balance Check

Model 3555B

c.Adjust A3R15 for 0dBm indication on the 3555B meter.

d.Change the 654A frequency to 1kHz. Change the 3555B FUNCTION switch to VF/Nm, 600 BAL. Compare the 3555B meter indication with the indication in step c. If any difference exists, adjust A3R15 to split the difference between these two indications.

NOTE

If the set is being operated from the ac line ground currents may be encountered on the low ranges, particularly if other instruments are connected in any way to the 3555B. In order to eliminate this problem, operate the set from its own internal battery or use the C MSG filter. If the C MSG filter is used, perform the filter calibration described in Paragraph 5-24and then perform the following step.

e.Change the 654A to -80dBm output .level at 1.00kHz. Change the 3555B RANGE switch to -80dBm. Adjust A3R26 for 0dBm indication on the 3555B meter.

f.Change the 654A to 135 BAL (150 BAL) and change the 3555B FUNCTION to 135 BAL (I50 BAL). Adjust A3R24 for 0dBm indication on the 3555B meter.

g.Change the 3555B RANGE switch to - 5OdBm, INPUT switch to TMS TERM, and the FUNCTION switch to VF/Nm 600 BAL. Change the 654A to 1kHz at an output level of -50dBm, 600 BAL. Adjust the AMPLITUDE control for exactly 0dBm indication on the 3555B meter.

h.Change the 3555B FUNCTION switch to 900 BAL without changing anything else. Adjust A3R20 for -0.15dBm indication on the 3555B meter.

5-21. FREQUENCY RESPONSE ADJUSTMENT.

a. The following adjustment consists of selecting fixed values for frequency compensation at 20Hz, 600 BAL, -70dBm and 20kHz, 600 BAL, -70dBm.

b.Connect the 654A 600 BAL output to the 3555B input. Set the 3555B controls as follows:

FUNCTION ............... VF/Nm 900 BAL INPUT............................. TMS, TERM RANGE ..................................... 0dBm

Section V

RESPONSE ............................. DAMP

c.Set the 654A (600 BAL) output level to 0dBm at a frequency of 20Hz. The 3555B meter should Section V indicate -0.1SdBm +0.3dBm. Note this indication.

d.Change the 654A output level to -70dBm at a frequency of 20Hz. Change the 3555B RANGE switch to -70dBm and change the FUNCTION to VF/Nm 600 BAL. The 3555B meter should indicate 0dBm +0.3dBm. Note the exact indication.

e.Compensation should be made between the 900 BAL, 0dBm check (step c) and the 600 BAL, -70dBm check (step d). To raise the level, increase the value of A3R72 until the 900 BAL 0dBm check indicates high by the same amount that the 600 BAL, - 70dBm check indicates low. The total difference should not exceed +0.3dBm.

5-22. COMMON MODE ADJUSTMENT.

a.Connect the equipment as shown in Figure

5-5and set the 3555B controls as follows: FUNCTION ................VF/Nm, 600 BAL INPUT...............................TMS, TERM RANGE ....................................... 0dBm

b.Set the 654A frequency to 20kHz and adjust the output level of the 654A for 0dBm indication on the 3555B meter.

c.Disconnect the left output terminal on the 654A and short the tip and ring together on the cable. Down range the 3555B RANGE switch for an on-scale indication.

d.Adjust A1C7 for minimum indication on the 3555B meter. This indication must be down at least 60 dB.

e.Change the 3555B FUNCTION switch to CARRIER, 600 BAL and change the 654A frequency to 100kHz.

f.Use the procedure described above and adjust A1C4 for minimum indication on the 3555B meter. This indication must be down at least 40dB.

5-23. BALANCE CHECK.

a.First check the balance as described in paragraph 5-13to be sure that the balance does not meet specifications. If it does, disregard this step. If it does not perform the following procedure.

b.Since there are no adjustments for balance it will be necessary to change the value of a fixed factory selected capacitor. To adjust the balance on the

5-9