Stanford Research Systems SR844, User Manual

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3-30 Reference Section
SR844 RF Lock-In Amplifier
Important!
The 2F detection frequency is limited to 50 kHz to 200 MHz. This corresponds to a REF
IN and REF OUT frequency range of 25 kHz to 100 MHz.
The absolute phase in 2F mode is not specified. However, the relative phase accuracy
generally applies.
Ref Z-In
This key selects the impedance of the External Reference Input (REF IN), either
50
Ω Ω Ω Ω
or
10 k
Ω
Ω Ω
Ω
|| 40 pF . The reference signal should be 0 dBm (sine) or 0.7 Vpp (pulse) for
proper locking. The SR844 will lock to other amplitudes with possible degradation in
phase accuracy and jitter.
OUT OF
RANGE This indicator is on whenever the External Reference input is out of the operating
frequency range (25 kHz to 200 MHz) or is not detected at the input due to insufficient
amplitude or non-periodic pulse shape. This only applies in External Reference mode.
UNLOCK This indicator is on whenever the SR844 is not locked.
In External Reference mode, this occurs when the REF IN frequency is changing or
unstable. In Internal Reference mode, this occurs when the internal reference frequency is
changed. The internal synthesizer requires time to lock to the new frequency.