QAM (Digital Demod)

Use the Format drop-down list to select a QAM Quadrature Amplitude Modulation (Quadrature Amplitude Modulation) modulation format to demodulate. The VSA supports 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM, 512-QAM, 1024-QAM, 2048-QAM, and 4096-QAM modulation formats.

Reliable Carrier Lock

This table shows the minimum Result Length and frequency offset values for reliable carrier lock for QAM signals:

Digital Modulation Format	Minimum Result Length (0 Hz frequency offset)	Maximum frequency offset (Result Length = 1000 symbols)
16-QAM	50 symbols	4.8% symbol rate
32-QAM	75 symbols	3.15% symbol rate
64-QAM	150 symbols	4.65% symbol rate
128-QAM	250 symbols	0.3% symbol rate
256-QAM	400 symbols	0.3% symbol rate
512-QAM	1000 symbols	0.15% symbol rate
1024-QAM	1000 symbols	0.15% symbol rate
2048-QAM	4000 symbols	0.1% symbol rate*
4096-QAM	4000 symbols	0.1% symbol rate*

*Using Low SNR Signal-to-Noise Ratio Enhancement is required to make frequency locking robust for this QAM format.

QAM formats with 512 or more states are very sensitive to noise. Even an 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. of approximately 2% can cause symbol detection errors in the algorithm. This can cause a positive bias on EVM (an EVM appears better than it really would be for that signal). Analysis of these higher-order QAM formats is not intended with a Signal to Noise Ratio of less than 40dB.