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Adjustment Procedures
5-46
2715 Spectrum Analyzer Service Manual
Adjust Downconverter Local Oscillator. Adjust R59 and R63 as follows:
1. Reconnect the 110 MHz input signal (from the RF Mother board) to the
Video Demod board 110M IN connector.
2. Move the input cable of the test spectrum analyzer from TP110M (on the
Video Demod board) to TP45M.
3. Set the test spectrum analyzer as follows:
Center Frequency 45 MHz
Reference Level --30 dBm
Span/Div 1 MHz
4. Initialize the 2715 setting by pressing UTIL 1 1.
5. Select the following settings on the 2715:
CENTER FREQUENCY 100 MHz
REFERENCE LEVEL 18.8 dBmV
RESOLUTION BANDWIDTH 1 MHz
SPAN ZERO
Calibrator Signal ON
Markers OFF
6. Activate the TOGGLE VD DAC LO/HI function by pressing UTIL525.
NOTE. When performing steps 7 through 10 you will be adjusting the operating
frequency and tuning range of the Downconverter Local Oscillator. While
making the adjusts, use menu item 5 (TOGGLE VD DAC LO/HI) to toggle the
frequency between the two values (41 and 47 MHz as indicated by the “41 SET”
or “47 SET” at the end of the menu line).
The object of the procedure is to set R63 and R59 so that the frequencies
produced in both states are each within 100 kHz of the nominal value.
7. Adjust the video demod BIAS (R63) so that the signal peaks, in both states
(41SETand47SET),arevisibleonthetestspectrumanalyzer’s screen. If
necessary adjust RANGE (R59) toward the counterclockwise end of its
rotation.
8. Adjust RANGE (R59) so that the two signal peak locations are 6.0 MHz
apart.
9. Adjust BIAS (R63) so that the lower frequency signal is located at 41 MHz
±100 kHz.
10. Alternately adjust R59 and R63 to eliminate interaction until the lower
frequency peak is at 41 MHz ±100 kHz and the upper peak is at 47.0 MHz
±100 kHz.