11. Down/Up Converter Adjustments

Down Converter Gain Adjustment

Note

If a gain problem is suspected in the 10 Hz to 1 kHz resolution bandwidths, perform the following procedure to test and adjust the gain through A4A6A2.

1.Place A4A6 on extender boards.

2.On the spectrum analyzer being tested, press QNST PRESET], and set the spectrum analyzer to the following settings:

CENTER FREQUENCY . . . . . . . . . . . . . . . . . . . . . . . . 20 MHz RESOLUTION BANDWIDTH . . . . . . . . . . . . . . . . . . . . . 1 kHz FREQUENCY SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz REFERENCE LEVEL . . . . . . . . . . . . . . . . . . . . . . . . -10 dBm INPUT ATTENUATION . . . . . . . . . . . . . . . . . . . . . . . . . . 10 dB

3.Connect an active probe to a second spectrum analyzer, and set the spectrum analyzer to the following settings:

CENTER FREQUENCY . . . . . . . . . . . . . . . . . . . . . . 21.4 MHz

RESOLUTION BANDWIDTH . . . . . . . . . . . . . . . . . . 100 kHz

FREQUENCY SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . ..200 HzREFERENCE LEVEL . . . . . . . . . . . . . . . . . . . . _ . . . -30 dBmINPUT ATTENUATION . . . . . . . . . . . . . . . . . . . . . . . . . . 10 dB

SCALE . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . LOG 1 dB/div

4.Measure the signal at A4A6A2TP4 using the active probe and record below. The signal level should be approximately -33 dBm.

Signal level at TP4

 

dBM

5.Change the center frequency of the spectrum analyzer used for measuring the signals to 3 MHz. Measure the signal at A4A6A2Pl-9. The signal level should be 10 dB f0.6 dB lower than the signal measured in the previous step.

Signal level at Pl-9

 

dBM

 

6.If the signal at A4A6A2Pl-9 needs adjusting, change A4A6A2R33. (Decreasing R33 ten percent increases the signal level by 0.6 dB.) Refer to Table 3-3 for the acceptable range of values for A4A6A2R33.

3-94 Adjustments