DVB QAM (Digital Demod)

Use the Format drop-down list to select a DVB QAM Quadrature Amplitude Modulation format that conforms to the DVB (Digital Video Broadcast (DVB) standard, EN 300 429. The VSA supports the following DVB QAM formats:

Format	DVB QAM signal format
DVB 16-QAM	16 QAM signals
DVM 32-QAM	32 QAM signals
DVB 64-QAM	64 QAM signals
DVB 128-QAM	128 QAM signals
DVB 256-QAM	256 QAM signals

The standard defines the bits that represent each state as follows:

The first two bits are differentially encoded so that pi/2 rotations in the QAM constellation do not affect detection of the two MSBs.
The LSBs are positioned to be rotation-invariant as defined in EN 300 429

I/Q Origin Offset Compensation

Unlike QAM, DVB QAM does not compensate for I/Q origin offset. When the demodulation format is DVB QAM, the VSA reports I/Q origin offset in the symbol table, but doesn't remove it from the measurement. When the demodulation format is QAM, the VSA reports I/Q origin offset in the symbol table AND removes it from the measurement.

To see the effects of I/Q origin offset on your DVB QAM signal, change the demodulation format to QAM. For example, if your signal is 16 DVB QAM, select 16-QAM to see the effects of I/Q origin offset removal on your signal.

The Error Vector Magnitude (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.) for DVB QAM will be higher than QAM because DVB QAM includes IQ origin offset in the measurement.

Reliable Carrier Lock

This table shows the minimum result length and frequency offset values for reliable carrier lock for DVB QAM signals:

Digital Modulation Format	Minimum Result Length (0 Hz frequency offset)	Maximum frequency offset (Result Length = 1000 symbols)
DVB 16-QAM	50 symbols	4.65% symbol rate
DVB 32-QAM	75 symbols	2.85% symbol rate
DVB 64-QAM	150 symbols	4.65% symbol rate
DVB 128-QAM	250 symbols	0.45% symbol rate
DVB 256-QAM	400 symbols	0.15% symbol rate