Freq Err (Digital Demod)

Freq Err (Frequency Error) shows the carrier's frequency error relative to the VSA's center frequency. This error data is displayed in Hertz and is the amount of frequency shift from the VSA's center frequency that the VSA must perform to achieve carrier lock.

Errors in RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). frequency, LO frequency, or digitizer clock rate can all appear as carrier frequency error.

Freq Err is computed using all points (including points between symbols).

Maximum frequency offset for reliable carrier lock

The following table shows the maximum frequency offset for which the demodulator will still be able to achieve reliable carrier lock when Result Length = 1000 symbols.

Digital Modulation Format	Maximum frequency offset (Result Length = 1000 symbols)
QPSK Quadrature phase shift keying	9.6% symbol rate
16 QAM Quadrature Amplitude Modulation	4.8% symbol rate
32 QAM	3.15% symbol rate
64 QAM	4.65% symbol rate
128 QAM	0.3% symbol rate
256 QAM	0.3% symbol rate
512 QAM	0.15% symbol rate
1024 QAM	0.15% symbol rate
2048-QAM	0.1% symbol rate*
4096-QAM	0.1% symbol rate*
16 DVB QAM	4.65% symbol rate
32 DVB QAM	2.85% symbol rate
64 DVB QAM	4.65% symbol rate
128 DVB QAM	0.45% symbol rate
256 DVB QAM	0.15% symbol rate

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