Agilent Technologies 8647A User Manual

7-24
Adjustments
Manual Adjustments
Motherboard Audio Path (All 8648A/B/C/D)
This adjustment calibrates the internal and external audio paths of the motherboard by
determining the full-scale (100%) DAC values required for the audio path calibration.
For internal modulation measurements, the DAC is set to a percentage, DAC Offset
Percentage, of its value. The percentage is 70% for the 8648A and 90% for the 8648B/C/D.
At each DAC value, the corresponding output depth/deviation is measured with the
measuring receiver and the slope of the DAC is calculated using the following:
The slope determines the actual value of the DAC required to set the modulation level at
the exact DAC Offset Percentage. The DAC is fine-tuned by measuring the output
depth/deviation and adjusting the DAC until the resulting depth/deviation is within a
specified tolerance. The final value of the DAC for internal modulation measurements is
calculated as follows:
The difference between internal and external modulation involves compensating for the
inaccuracies of the external function generator. First, the voltage level of the function
generator is set to 1.083 volts (not 1V) to compensate for the mismatch between its
600 ohm output and the 50 ohm input of the DUT. Then, the actual voltage is measured
and the target deviation set at DAC Offset percentage of the measured voltage. The level
DAC is adjusted for DAC Offset Percentage deviation and then the 100% level DAC value
for external modulation measurements is calculated as shown:
Required Test Equipment
• Function Generator
•DVM
• Measuring Receiver
S
lope
Measured Depth
()
Deviation
()⁄
DAC Offset Percentage
100
---------------------------------------------------------


409
5
×
-----------------------------------------------------------------------------
----
=
D
AC Value
int
DAC Value at DAC Offset Percentage
DAC Offset Percentage
100
---------------------------------------------------------


-----------------------------------------------------------------------------------------
---
=
D
AC Value
ext
DAC Value at DAC Offset Percentage
Actual 3325B Voltage
DAC Offset Percentage
100
---------------------------------------------------------


×
-----------------------------------------------------------------------------------------------------------------------
----
=

Agilent Technologies 8647A Specifications

General

Brand	Agilent Technologies
Model	8647A
Category	Test Equipment
Language	English