R&S FSMR, Operating Manual

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R&S FSMR TRACe Subsystem
1313.9723.12 6.1-227 E-1
TRACe:IQ Subsystem
The commands of this subsystem are used for collection and output of measured IQ data. A special
memory is therefore available in the instrument with 512k words for the I and Q data. The measurement
is always performed in the time domain (span = 0 Hz) at the selected center frequency. The number of
samples to be collected can be set. The sample rate can be set in the range from 15.625 kHz to 32
MHz. Prior to being stored in memory or output via GPIB, the measurement data are corrected in terms
of frequency response.
Depending on the sample rate, the following maximum bandwidths can be obtained during the
measurement.
Sample rate Max. bandwidth Notes
32 MHz 9.6 MHz
16 MHz 7.72 MHz
8 MHz 4.8 MHz Signals outside the given bandwidth are
folded back into the useful band due to the
anti-aliasing filter.
4 MHz 2.8 MHz
2 MHz 1.6 MHz max. bandwidth = 0.8 * sample rate for
sample rate 2 MHz
1 MHz 800 kHz
500 kHz 400 kHz
250 kHz 200 kHz
125 kHz 100 kHz
62.5 kHz 50 kHz
31.25 kHz 25 kHz
15.625 kHz 12.5 kHz
Due to the sampling concept (21.4 MHz IF, 32 MHz Sampling rate), the image frequency is suppressed
only by the 10 MHz analog IF filter. When applying an input signal at the edge of the 10 MHz band (+5
MHz from center), the image frequency appears 800 kHz above the input signal.
The image frequency in MHz is calculated as follows:
signal center image
f MHz) 5.4 (f 2 f
+ =
where
f
image
= image frequency in MHz
f
center
= center frequency in MHz
f
signal
= frequency of the signal to be measured in MHz
For correct operation the RF input signal shall be limited in bandwidth. Signals more than 5.4 MHz
above the center frequency will be mirrored into the 10 MHz pass band.
For additional bandwidth limitation of the measurement data the analog filters (RBW
300 kHz) are
available.
I Memory
512 k
Processor
Analog
IF filter
Bandwidths
300 kHz
1 MHz
3 MHz
10 MHz
Analyzer IF
20.4 MHz
A
D
A/D
converter
32 MHz
sampling
clock
Digital down conversion
+ decimation
cos
sin
decimation
filters
NCO
20.4 MHz
Q Memory
512 k
sampling rate
32 MHz / 2 n
n = 0 ... 11
Data aquisition hardware
I data
Q data
Trigger
Fig. 6.1-1 Block diagram illustrating signal processing in analyzer