Ref Level - HP 85020A Operating And Service Manual

Model 85020A/B
Service
Procedure
1. Remove the silicone rubber seal from the two potentiometers to
gain access to the screwdriver slots.
2. Connect the equipment as shown in Figure 8-7. If the
Directional Bridge is an 85020B, connect the Model 11852A
50-ohm to 75-ohm minimum loss pad between the step attenuator
and the input port of the Directional Bridge. Allow the
equipment to warm up for 30 minutes.
3. On the 8350A/B, press
[INSTR PRESET] [SHIFT] fCWj [2] [0] [0]
[MHz]
to set the signal to swept CW. Press
[SWEEP TIME] [1]
[5] [0] [ms].
Press [Lil
MOD]
to turn on squarewave modulation.
4. Set the 8756A as follows:
CHANNEL 2 ..... . OFF
CHANNEL 1 ON
MEAS PWR .. A
REF LEVEL .. 0
SCALE.. . 10 dB/DIV
5. Set the attenuator to 0 dB. Set the REFERENCE POSITION near
the top of the screen. Adjust the REFERENCE LEVEL to coincide
with the REFERENCE POSITION. (The reference level should be 0
dBm +2 dB with an input signal of +13 dBm, for the 85020A. For
the 85020B, the reference level should be -6 dBm +2 dB.)
6. Set the attenuator to 20 dB. On the 85020A/B, adjust A2R2 (Z)
to position the trace on the graticule line 20 dB below the
reference.
7. Set the attenuator to 0 dB. On the 85020A/B, adjust A2R4
(GAIN) to reposition the trace at the reference.
8. Iterate between the last two steps until the trace is on the
graticule line +0.5 dB at both steps.
9. Step the attenuator in 10-dB steps to 40 dB. Check that the
traces at all steps are spaced at 10 dB intervals +0.5 dB on
the displav. If the trace is not tracking at 10-dB intervals,
iterate between 0 dB and 40 dB of attenuation while
compensating the GAIN and Z adjustments as described above.
8-15