A Gain Calibration; Preliminary; Ac Gain - Stanford Research Systems SR446 Operation And Service Manual

Appendix A Gain Calibration
A.1 Preliminary
WARNING
A.2 AC gain
SR446 400 MHz Programmable Gain Preamplifier
This chapter describes the equipment and procedures to trim the overall
gain of the SR446.
All equipment should be powered on and warmed up for at least 2 hours
prior to performing calibration. The SR446 should be in a temperature‑
stable ambient indoor environment, and the offset calibration procedure
(see § 1.3.1) should be performed within 24 hours prior to gain calibration.
Adjusting the gain calibration requires removing the protective cover
from the amplifier while power is applied.
performed by a qualified technician.
Gather the following instruments and accessories:
1. SR865A 4 MHz DSP Lock‑in Amplifier
2. Two 1 m (approximate) long RG58 coax cables with BNC connectors
3. BNC Tee adaptor
4. BNC 50 Ω terminator
The gain steps of the SR446 are controlled by variable‑gain amplifier
U302, and cannot be trimmed.
inverting output, and separately the non‑inverting output, can be
trimmed by adjusting internal trimmers R412 and R512 respectively
(see Figure A.1). The procedure described here adjusts the gain at
+ 20 dB, and at 1 MHz.
To configure the SR865A to calibrate the amplifier AC gain:
1. Both the SR865A and the SR446 should be powered on and
warmed up, ideally for at least 2 hours.
2. Connect a 50 Ω terminator to the BNC tee, and connect the tee to
the "A" input of the SR865A.
3. Reset the SR865A by pressing the [Save Recall] button. Then touch
the [Recall default] tile at the upper‑left of the screen, and touch
[Confirm].
This should only be
However, the overall gain for the
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