X, Y, R, Θ Θ Θ Θ And Dbm - Stanford Research Systems SR844 User Manual

X, Y, R, θ θ θ θ and dBm
This measurement is designed to use the internal oscillator and an external signal source to explore some
of the signal types. You will need a synthesized signal generator cable of providing 200 mVrms (0 dBm)
sine waves at 100 kHz into a 50
BNC cables.
Specifically you will display the lock-in outputs when measuring a signal that has a frequency close to,
but not equal to, the internal reference frequency.
Note: The last few items in this section require that the signal generator have a Sync output; if you are
using a signal generator that has a single output only, you can split the output using a BNC Tee (or a
power splitter or a directional coupler).
1 Disconnect all cables from the SR844.
If the power is off, turn it on. Wait for self-
tests to complete.
2 Press Shift then Recall (PRESET) to restore
factory presets.
Use the knob to adjust the SR844 reference
3
frequency to 100 kHz.
Press Sensitivity Down.
4
Press Time Constant Down twice until the
time constant is 10 ms.
5 Turn on the external signal generator and set
the frequency to 100 kHz exactly, and the
amplitude to 200 mVrms, 0 dBm, or
600 mVpp into 50
really matter. Low-frequency signal generators
may have waveform selection (select sine
wave) and DC offset (set it to zero). If the
signal generator offers modulation, make sure
it's off.
Ω
load (the DS335 from Stanford Research Systems will suffice), and
Ω
. The exact value doesn't
X, Y, R, θ θ θ θ and dBm
Turn on the unit.
The factory preset configuration is:
1 Vrms sensitivity.
100 ms, 12 dB/oct time constant.
Internal Reference at 1.00 MHz.
Ω
Signal Input 50 .
We are using a low reference frequency so that the
intrinsic frequency difference between the SR844
and the signal generator has a smaller absolute
value.
The SR844 sensitivity should now be 300 mVrms.
We need a shorter time constant to measure the
output signal.
While not phase-locked, the signal generator and
SR844 should be at very nearly the same frequency;
the slight frequency difference will be manifested as
a changing relative phase.
SR844 RF Lock-In Amplifier
1-9