Stanford Research Systems DS345, Manual

Page: 98 / 139

Calibration
6-7
6) Set the DS345 to 625mV offset. Measure the DC voltage. The new value
for calbyte 9 = old calbyte 9 * Vref/(16 * Vdc).
7) Set the DS345 to 312mV offset. Measure the DC voltage. The new value
for calbyte 10 = old calbyte 10 * Vref/(32.05 * Vdc).
8) Set the DS345 to 156mV offset. Measure the DC voltage. The new value
for calbyte 11 = old calbyte 11 * Vref/(64.1 * Vdc).
9) Set the DS345 to 78mV offset. Measure the DC voltage. The new value
for calbyte 12 = old calbyte 12 * Vref/(128.21 * Vdc).
10) Set the DS345 to 39mV offset. Measure the DC voltage. The new value
for calbyte 13 = old calbyte 13 * Vref/(256.41 * Vdc).
Carrier Null Calibration
This calibration nulls the carrier feedthrough of the DS345's frequency dou-
bler. This calibration depends on frequency and is calibrated at 98 frequency
points in the DS345's frequency range. This calibration must be done before
the amplitude calibrations.
1) Set the DS345 to sine wave, 1 kHz, 8 Vpp, 0 V offset. Connect the
DS345's output to the FFT spectrum analyzer using a 50
Ω
terminator. Set
the analyzer to display 0 to 2 kHz.
2) Adjust calbyte 314 to minimize the 1 kHz carrier amplitude.
3) Connect the DS345's output to the RF spectrum analyzer. Set the
DS345's frequency step size to 312500 Hz. Set the frequency to 313500 Hz.
At 96 frequencies between 313500 Hz and 30,001,000 Hz in 312500 Hz
steps repeat the following procedure.
4) Set the spectrum analyzer center frequency to the programmed frequency/
2. Set the span to 100 kHz.
5) Adjust the appropriate calbyte to minimize the carrier frequency compo-
nent at f/2 (ignore any nearby spurs). The calbyte has a range of 0 to 4095.
The calbyte number for a particular frequency is: 314 + (f - 1000Hz)/312500
Hz (that is 313500 Hz = 315, 626000 Hz = 316, etc.).
6) Step to the next frequency, and reset the analyzer. Continue until
30,001,000 Hz and calbyte 410.
7) Set calbyte 411 to the same value as calbyte 410.