Measuring DVB-T Signals - Digital Video and Audio Broadcasting Technology - page 396

fed with 90 degrees carrier phase and the two modulation products added
together result in the COFDM signal cofdm(t).

I

Re(f)

re(t)

+

IFFT cofdm(t)

im(t)

Im(f)

Q

90°

Fig. 21.8. COFDM modulator

Fig. 21.9. I/Q imbalance

The signal branches re(t) and im(t) must exhibit exactly the right ratios
of levels with respect to one another. The 90 0 phase shifter must also be set
correctly. And there must not be any DC component superimposed on the
re(t) and im(t) signals. Otherwise, so-called I/Q errors will occur. The re-