Agilent Technologies 856290216 service manual Video Off set

Total gain can be measured by injecting the specified power into A4J3 and measuring the total gain provided by A4U201C and A4U201E. The following procedure provides a means of troubleshooting the linear amplifiers:

1. On the HP 85623 spectrum analyzer, press c-1, (SPAS3), ZEXQ SF&N, a),

TP ADJ OFF, (FREQUENCY), 1 (GHz), (m), -50 dBm, LINW, MORE, AMFTD UNITS, [dem, and [AMPLITUDE).

2.Disconnect W27 (coax 3) from A4J3 and connect the output of a signal generator to A4J3.

3.Set the signal generator controls as follows:

Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6 dBm Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7MHz

4.Simultaneously decrease the signal generator output and HP 85623 spectrum analyzer REF LVL in 10 dB steps to -90 dBm. At each step, the signal displayed on the spectrum analyzer should be within one division of the previous position.

5.If a problem exists, isolate it by comparing the actual gain of A4U201C and A4U201E with those listed in the above gain guidelines.

6.Reconnect W27 (coax 3) to A4J3.

Video Off set

Refer to function block P of A4 Log Amplifier Schematic Diagram (sheet 3 of 4) in the

HP 8560 E-Series Spectrum Analyzer Component Level Information.

The circuit provides a programmable video offset, with a step size of 5 mV, from -300 mV to i-900 mV.

1.On the HP 85623 spectrum analyzer, press (PRESET), (SPAN), ZEND SPAN, (-1, 1 m), @iZiiKZ), -50 dBm, (CAL), IF AD3 OFF.

2.Disconnect W27 (coax 3) from A4J3 and connect a signal generator to A4J3.

3.Set the signal generator controls as follows:

Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +lOdBm Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7MHz

4.Simultaneously decrease the signal generator output and HP 85623 spectrum analyzer reference level in 10 dB steps down to -110 dBm. At each step, the signal displayed on the spectrum analyzer should be close to the reference level.

5.Reconnect W27 (coax 3) to A4J3 and cycle the spectrum analyzer power. Press STOP NJ?<CN when it appears.

6.On the HP 85623 spectrum analyzer, press (K), SINGLE, (CAL), and IF A1)J DFF .

7.The offset DAC, A4U102 pin 2, should now be at its default value of approximately t2.45 V. The voltage at U601 pin 3 should be approximately 0 V for a DAC output of 2.45 V.

8.If this default offset voltage is incorrect, DAC U102 is the most probable cause.

IF Section 9-15