About Fixed Equalization (User Correction, Playback User Correction)

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Fixed Equalization applies a fixed FIR Finite Impulse Response equalization filter to the time data of the specified Measurement Channel. The filter is defined by its frequency response rather than by its impulse response. The frequency response must be stored in a data register.

Fixed equalization can be used for the following:

to normalize frequency response measurements
to compensate for channel differences in two-channel time domain measurements such as those required for Complex Stimulus-Response Measurements
in conjunction with Adaptive Equalization in digital demodulation measurements, for example to isolate channel response from transmitter and receiver response.

Fixed equalization is different from the adaptive equalization available with some digital demodulation formats. Fixed equalization:

is always available
is applied to the time data along with Time Corrections and affects any measurement result (except raw main time)
is not adaptive (like in Digital Demod) and the filter must be defined
can be applied either to zoomed or baseband measurements

A FIR filter is constructed from the frequency response data stored in a data register. The FIR filter is 200 taps long.

Absolute or relative frequency mapping

If possible, the equalizer response is defined using the portion of the register data that falls within the current measurement span. For example, if the data register covers frequencies from 200 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second. to 236 MHz and the measurement span is 6 MHz wide centered at 210 MHz, then the register data from 207 MHz to 213 MHz is used to define the equalizer response. This is an example of absolute frequency mapping.

If the same register data is used but measurement center frequency is then changed to 70 MHz, then relative frequency mapping must be used. The center frequency of the register data is mapped to the measurement center frequency and an equivalent span of data is taken. In this example, register data from 215 MHz to 221 MHz is used as though it covered a frequency span of 67 MHz to 73 MHz.

Relative frequency mapping is used if some or all of the measurement span falls outside the data register's frequency span. It can be desirable when measuring across frequency converters but can be surprising otherwise. Be careful to use a measurement span that is equal to or narrower than the span of the data register.