Tektronix RSA5100A Series Printable Help page 302

APCO P25 Analysis
How to Select Filters
In a signal transmitter/receiver system, the baseband signal might be filtered for bandwidth limiting or for
another kind of necessary shaping that needs to be applied. Normally, a filter in the transmitter (Ft) and a
filter in the receiver (Fr) are applied.
The Measurement Filter setting in the analyzer corresponds to the baseband filter in the receiver (Fr): This
setting tells the analyzer what filter your receiver uses. When the analyzer is set to the same filter used by
the receiver, the analyzer sees the signal as your receiver would. The Measurement Filter setting should be
the same as the filter used in the receiver under normal operation (as opposed to testing).
The Reference Filter setting in the analyzer corresponds to the baseband filter in the transmitter-receiver
combination (Fr * Ft). The baseband filter for the transmitter-receiver combination is often referred to as
the System Filter. This filter is called the reference filter because it is used to recreate a reference signal
that is compared to the received signal. This recreated reference signal is the ideal signal with Fr * Ft
applied; differences between this ideal signal and the received signal enables the determination of signal
quality, such as modulation fidelity measurements.
Filter Parameter (C4FM only)
The filter parameter specifies the alpha for the Raised Cosine filter when selected as the Reference filter.
Some filter types have a fixed parameter value that is specified by industry standard, while other filter types
by definition have no filter parameter. For filter types with no filter parameter, there is no filter parameter
control present in the control panel. The recommended Reference filter for C4FM is Raised Cosine and the
corresponding filter parameter for C4FM is 0.2.
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Modulation Params Tab - P25
RSA5100A Series Printable Help