Stanford Research Systems SR844, User Manual

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3-34 Scan - Rel
SR844 RF Lock-In Amplifier
Scan and Rel
Overview
Scans
The SR844 offers the facility of doing a manual frequency scan covering up to 11 frequency points. This
facility is available
only in the Internal Reference mode. Frequency scans are a convenient method for
making repeated measurements over a set of frequencies. For example, measurements of device noise or
frequency response using REF OUT as the signal source.
The set of scan frequencies are specified by a start frequency, a stop frequency and the number of points.
The start frequency and stop frequency may be anywhere within the operating range of the instrument,
25 kHz – 200 MHz. The SR844 will select the frequency points by interpolating geometrically between
the start and stop frequencies. The following equation gives the frequencies F
i
for i=0 to N–1, where N
≥
2
is the number of points.
F F
F
F
i start
stop
start
i
N
= ×






−
1
Here F
start
and F
stop
are the start and stop frequencies respectively. The geometric interpolation is
appropriate for wide frequency intervals, and is close to linear for narrow frequency intervals. The
interpolated frequencies are rounded to the resolution of the internal frequency
source.
The SCAN MODE indicator is on while a scan is in progress. Use the Scan
Set
key to setup a scan. Scan setup is not permitted while a scan is in progress.
Use the Start/Step key to start a scan and to step through the frequencies. To
stop a scan without going through all the frequencies, use
OFF
(
Shift–
Scan Set ).
Rels
At each scan frequency, a stored measurement setup, or Rel Configuration
(sensitivity, reserve, etc.), can be recalled. In addition, stored offsets (Rel Values) may be applied to the
signal. XY Rel Values are stored X and Y offsets. R
θ
Rels are stored R[dBm] and
θ
offsets. Rel Values
can be stored for each scan frequency.
To store Rel Values at the current scan frequency:
•
Use the Store XY key to Auto Offset X and Y and store the offsets as XY Rel offset values. The
XY READY
indicator is on when XY Rel Values have been stored at the current scan frequency. This
also stores the Rel Configuration (sensitivity, reserve, etc.).
•
Use STORE R[dBm]
θ
( Shift–Store XY ) to Auto Offset R[dBm] and Auto Phase the reference and
store the results as R[dBm] and
θ
Rel offset values. The
R[dBm]
θθθθ
indicator is on when R[dBm]
θ
Rel
Values have been stored at the current scan frequency. This also stores the Rel Configuration
(sensitivity, reserve, etc.).