Rohde & Schwarz R&S FSL3 - Bandwidths; Measurement Filter (Meas Filter

R&S FSL Bluetooth Measurements (Option K8)
1300.2519.12 2.41 E-11
The measurements are performed by passing the following signal processing steps:
 LAP (Lower Address Part) trigger detection

Resampling
 Channel filtering
 Automated packet and bit pattern detection
 Limit check
 Parallel display of measurement curves and numeric results on the screen
Fig. 2-1 shows the R&S FSL hardware from the IF to the processor. The analog IF filter is fixed to
20MHz. The A/D converter samples the 20 MHz IF signal with a sampling frequency of 65.83 MHz.
Low pass filtering is performed after the signal has been down–converted into the complex base band
and the data rate is reduced in the sequence. The amount of decimation depends on the selected
oversampling factor = points / symbol. The default setting is 4, resulting in a 4 MHz sampling rate. For
EDR–measurements, the oversampling factor is always fixed to 4. The resulting I/Q data are stored in a
memory of 512 k words for I and Q respectively. The hardware trigger (external or IF power) controls
the memory access.
I Memory
512 k
Processor
Analogfilter
Bandwidths
20 MHz
Analyzer IF
47,9 MHz
A
D
A/D
converter
65,83 MHz
sampling
clock
Digital down conversion
+ decimation
cos
sin
decimation
filters
NCO
47,9 MHz
Q Memory
512 k
sampling rate
65,83 MHz / x
Data aquisition hardware
I data
Q data
Trigger
SW -
Resampler
Fig. 2-29 Block diagram of the signal processing architecture of the R&S FSL
Bandwidths
The Bluetooth RF Specification defines a minimal bandwidth of 3 MHz. The digital bandwidth depends
on the selected oversampling factor (= points / symbol). With the default setting of 4, the digital
bandwidth is 3 MHz. This digital filter has a flat amplitude characteristics and does not affect the
frequency deviation of the signal.
Measurement Filter (Meas Filter On)
The RF Specification allows high distortion power in the first adjacent channels. The 3 MHz filter does
not suppress this kind of distortion, which leads to a high interference in modulation. Therefore a
precise measurement of the frequency deviation is not possible.
In order to obtain correct deviation results, the spectrum analyzer supplies an optional filter with a
passband only appropriate for the channel to measure. This filter is used by default. The Bluetooth
spectrum has a bandwidth of 1 MHz. The filter is flat within 1.04 MHz (ripple: only 0.02 dB) and has
steep edges. This measurement filter is not dependent on the selected oversampling factor. As a result