Agilent Technologies E8247C, User Manual

Page: 170 / 220

160 Chapter 7
Custom Real Time I/Q Baseband
Working with Phase Polarity
Working with Phase Polarity
To Set Phase Polarity to Normal or Inverted
1. Press
Mode
>
Custom
>
Real Time I/Q Baseband
>
More (1 of 3)
>
Phase Polarity Normal Invert
.
Phase Polarity Normal Invert enables you to either leave the selection as Normal (so that the phase
relationship between the I and Q signals is not altered by the phase polarity function), or set to Invert and
invert the internal Q signal, reversing the rotation direction of the phase modulation vector.
When you choose Invert, the in-phase component lags the quadrature-phase component by 90° in the
resulting modulation. Inverted phase polarity is required by some radio standards and it is useful for
lower sideband mixing applications. The inverted selection also applies to the I, I-bar, Q, and Q-bar
output signals.
Working with Differential Data Encoding
The Diff Data Encode Off On menu enables you to toggle the operational state of the signal generator’s
differential data encoding.
• When set to Off, data bits are not encoded prior to modulation.
• When set to On, data bits are encoded prior to modulation. Differential encoding uses an exclusive-OR
function to generate a modulated bit. Modulated bits will have a value of 1 if a data bit is different from
the previous bit or they will have a value of 0 if a data bit is the same as the previous bit.
This section provides information about the following:
• “Understanding Differential Encoding”
• “Using Differential Encoding” on page 165
Understanding Differential Encoding
Differential encoding is a digital-encoding technique whereby a binary value is denoted by a signal change
rather than a particular signal state. Using differential encoding, binary data in any user-defined I/Q or FSK
modulation can be encoded during the modulation process via symbol table offsets defined in the
Differential State Map.
For example, consider the signal generator’s default 4QAM I/Q modulation. With a user-defined modulation
based on the default 4QAM template, the
I/Q Values
editor contains data that represent four symbols (00,
01, 10, and 11) mapped into the I/Q plane using two distinct values, 1.000000 and -1.000000. These four