Demod Tab (Flex Frame - Basic Mode)

The Demod tab configures the Flex Frame measurement characteristics.

Modulation sets the modulation for the entire frame. If you select Custom, another drop-down appears to select a custom modulation. If no custom modulations exist, you can click Add Custom Modulation to add a new custom modulation to the Custom Modulation tab.

BPSK Binary phase shift keying - A type of phase modulation using 2 distinct carrier phases to signal ones and zeros.
QPSK Quadrature phase shift keying
16-QAM Quadrature Amplitude Modulation
64-QAM
256-QAM
1024-QAM
8-PSK Phase Shift Keying: A broad classification of modulation techniques where the information to be transmitted is contained in the phase of the carrier wave.
Custom - selecting Custom displays a dropdown containing custom modulations created in the Custom Modulation tab. If there are no custom modulations, you can click Add Custom Modulation to add a new custom modulation tab. The VSA will automatically switch to the Custom Modulation tab. You can also Import a custom modulation.

Default: BPSK

Range: BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM, 1024-QAM, 8-PSK, Custom

Custom Name (when Modulation is set to Custom) provides a drop-down list of Custom Modulation formats.

Import... (when Modulation is set to Custom) opens a dialog to import a custom modulation format. Imported modulation formats will be added to the Custom Name drop-down list to select a custom modulation format.

The same Import functionality is available in the Custom Modulation tab, which also provides constellation summaries and a means of managing and exporting custom modulations.

Symbol Rate sets the frame symbol rate in Hz.

Default: Depends on the Current Analyzer Configuration

Transmit Filter specifies the filter applied at the transmitter and sets the combination of Measurement Filter and Reference Filter (see the Filter tab) accordingly.

Root-raised Cosine - Measurement Filter will be also set to Root-raised Cosine and Reference Filter will be set to Raised Cosine (the combination of Transmit Filter and Measurement Filter).
Raised Cosine - Measurement Filter will be set to None and Reference Filter will be set to Raised Cosine.

If there is some other combination of Tx and Rx filters, "(other combination)" will be shown, indicating that you need to go to the Filter tab to see what is set.

Equalization

Off - equalization is not performed. There is no tracking for equalization impulse response, so the equalization impulse response is re-calculated for each run.
Track - equalization is performed. Equalization implulse response is updated run by run (based on data).
Hold - equalization is performed. Equalization impulse response is held to the most recent equalization impulse response estimate.

Choices: Off, Track, Hold

Default: Off

The Reset button will reset the eq channel response to be flat (no correction).

These settings are also available on the Compensation tab.

Convergence (only useful when Equalization is on) controls the rate of convergence of the adaptive equalizer of the digital demodulation measurement. This setting is also available on the Compensation tab.

Convergence determines how quickly the equalization filter coefficients converge to the estimated values for each measurement. Larger values converge faster but might not be as consistent, based on noise in the data. Smaller values converge more slowly but provide a more consistent equalization filter for a given channel. This provides a trade-off in the number of measurements required for convergence of the equalization filter taps, and the stability of those taps. For more information, see Convergence (Digital Demod).

Default: 1E-06

Eq Filter Taps This is the total number of taps in the equalization filter, just like DigDemod or Custom IQ (to relate to Normalized Delay Spread, Eq Filter Taps = 2* normalized delay spread + 1). This setting is also available on the Compensation tab.

Default: 3 symbols

Enable Cross-Correlated EVM (available when Pattern Search is enabled and 2 channels are configured) when enabled, computes EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. by combining the results of two different measurements of the same signal so as to reduce the noise contributed by the acquisition hardware. This procedure causes the ccEVM value to primarily contain the noise coming from the DUT Device under Test: An acronym used to describe some type of electrical apparatus connected to test instrumentation. The apparatus can range from a single component to a complex subsystem such as a mobile phone, base station or MSC. (or source and DUT, in the case of an amplifier). In Basic mode, the channel mapping is tied to ch1 and ch2 in case you have more than 2 channels in your channel configuration.

Default: disabled (cleared)