User-defined Filters (Digital Demod)

MeasSetup > Digital Demod Properties > Filter > Reference Filter

The VSA allows use of a filter in your design for the I/Q measured filter or the I/Q reference filter. Typical applications for user-defined filters include:

Custom filters other than those provided. In this case both measured and reference filters are user defined.
Modified filters that are based on the raised cosine filter but add channel equalization. In this case, the measure filter is a user-defined filter and the reference filter is standard.

Creating and using a User-defined filter

To use a user-defined filter, create a trace file containing the time-domain impulse response of the desired filter.

The trace data file must satisfy the following criteria:

Only be real data, not complex
Only be time-domain data. If the data domain type cannot be determined from the trace file (unknown domain), the VSA will default to time-domain data. If any other domain is used, for example the frequency-domain, the VSA will reject the user-defined trace file and use a root raised cosine filter as the Measurement Filter and a raised cosine filter as the Reference Filter.
Contain > 0 and £ 20 symbols (401 samples) in overall length. However, if the filter alpha is < 0.4, the trace length must be £ 40 symbols (801 samples) in overall length.
Contain 20 samples-per-symbol. For example, 401 samples = 20 symbols at 20 points-per-symbol.
Use an odd number of points so that the center of the impulse is positioned on a symbol, this would be the 201st point in a 401 point trace. The middle sample is assumed to be at t = 0.

If the trace file does not satisfy all of previously mentioned criterion, the VSA will reject the user-defined trace file and default to using the Root Raised Cosine filter as the Measurement Filter and the Raised Cosine filter as the Reference Filter. The VSA will not indicate (display a status message) that the user-defined trace file was rejected and that the default filters were used in the measurement.

The VSA will not indicate (display a status message) that the user-defined trace file was rejected.

After creating the trace file, store it in a data register. Then select "User Defined" as the Measurement Filter and select the Data Register that contains the trace file to be used as the "User-defined" filter. Repeat these settings for the Reference Filter (if required).

Accuracy of user-defined filters is undefined. In addition, the value of Alpha / BT has no effect on user-defined filters.

APCO-25 Phase 2 RC filter

A custom RC Radio Configuration: defines the physical channel configuration of cdma2000 (IS-2000) signals. Each RC specifies a set of data rates based on either 9.6 or 14.4 kbps. RC1 is the backwards-compatible mode of cdmaOne for 9.6 kbps voice traffic. It includes 9.6, 4.8, 2.4, 1.2 kbps data rates and operates at Spread Rate 1 (SR1). RC3 is a cdma2000 specific configuration based on 9.6 kbps that also supports 4.8, 2.7, and 1.5 kbps for voice, while supporting data at 19.2, 38.4, 76.8, and 153.6 kbps. RC3 also operates at SR1. For more information see Keysight application note "Performing cdma2000 Measurements Today". filter is included for use with APCO-25 Phase 2 HDQPSK signals. See APCO25 Phase 2 RC Filter for information on how to use this filter.