Tektronix TSG4102A, User Manual

Page: 72 / 99

Digital communications
Table 10: PRBS generating polynomials (cont.)
Length Polynomial
29 x
29
+ x
27
+ 1
30 x
30
+ x
29
+ x
16
+ x
4
+ 1
31 x
31
+ x
28
+ 1
32 x 32 + x 31 + x 18 + x 10 + 1
Pattern data Digital modulation subtypes can also be modulated with 16-bit patterns. The
current pattern is shown as hexadecimal digits. Once selected, the pattern may
be edited from the front panel by modifying each hexadecimal digit. The default
pattern is the binary sequence 01010101 01010101, which corresponds to the
hexadecimal value 0x5555.
User data User data can be downloaded into on-board SRAM and subsequently saved into
FLASH. If user waveforms are available for the selected modulation subtype,
they can be selected as a modulation function. You can read more about user
waveforms. (See page 30,
Arbitrary waveform user presets .) and (See page 57,
User waveforms, constellations, and fi lters .)
Modulation rate The modulation rate is associated with the current modulation type. For digital
modulation subtypes, this is the symbol rate; otherwise, it is the frequency or
bandwidth of the selected waveform.
Modulation deviation
(scale factor)
For FSK or CPM modulations, the modulation deviation identi fi es either the peak
deviation or the modulation index of the modulation as indicated. For all other
types of vector modulation, the power of the modulated waveform is de
fi ned
by the constellation, the fi ltering, and the carrier power. However, in order to
prevent clipping when waveforms are passed through the pulse shaping fi lters, the
constellations are reduced by a factor of 7/16. The resulting scale is de fi ned to
have a scale factor of 1.0. Output power calibration assumes a scale factor of 1.0.
Normally, this scale factor need not be changed, because the carrier power is set
with the Amplitude button. However, you can alter this scale factor, if desired.
Larger scale factors will use more of the available digital phase space and reduce
the quantization noise of the
fi nal waveform. This might also be desirable if
the amplitude is already at max power and you still need a bit more power. The
risk is that the pulse shaping
fi lters will occasionally clip the waveform to the
rail during large excursions.
56 TSG4100A Series RF Signal Generators User Manual