Operating instructions

More Complex Programming Examples R&S ESCI
1166.6004.12 7.40 E-1
The image frequency in MHz is calculated as follows:
signalcenterimage
fMHz)5.4(f2f −+⋅=
where
f
image
= image frequency in MHz
f
center
= center frequency in MHz
f
signal
= frequency in MHz of signal measured
For correct measurements, the RF input signal must be band-limited. Signals spaced more than
5.4 MHz from the center frequency are reflected into the passband of the 10 MHz filter.
Analog prefilters (bandwidth ≥300 kHz) are available to provide additional band-limiting of the signal
measured.
The following example shows the steps necessary to collect data at a predefined sampling rate and
read it from the I/Q memory.
Data is output in the form of voltage values referred to the analyzer input. Data can be read in binary or
ASCII format.
In binary format, the length information carried in the message header is evaluated and used for
calculating the x axis values.
In ASCII format, only a list of voltage values is output.
Binary data is read in three steps:
1. The number of digits carrying the length information is read.
2. The length information itself is read.
3. The trace data is read.
This procedure is necessary with programming languages like Visual Basic which support only
structures of identical data types (arrays), whereas the binary data format uses different data types in
the header and the data section.
Note: The arrays for measured data are dimensioned in such a way that they can accommodate
2 * 128 k * 4 byte.
REM ************************************************************************
Public Sub ReadIQData()
'--------- Create variables -----------------------------------------------
Dim IData(131072) As Single 'Buffer for floating-point
'I data (= 128*1024 bytes)
Dim QData(131072) As Single 'Buffer for floating-point
'Q data (= 128*1024 bytes)
'Note:
'Visual Basic cannot read in
'data volumes larger than
'128k words!
Dim digits As Byte 'No. of digits as length
Dim IQBytes As Long 'Length of trace data in bytes
Dim IQValues As Long 'No. of meas. values in buffer
asciiResult$ = Space$(6553600) 'Buffer for ASCII I/Q data
'(= 25*2*1024 bytes)
result$ = Space$(100) 'Buffer for simple results
'--------- Default setting ---------------------------------------