Some customers require high carrier suppression when using the external I/Q modulation inputs. Tests have shown that the SRS SG384 (with Option 3, External I/Q modulation inputs) can provide more than 70 dB of carrier suppression with careful control of the offset voltage on the external I/Q modulation inputs. SRS_SG384_150514 The photo above shows the power signal envelope of a SRS SG384 in the External I/Q modulation mode. The carrier is 0 dBm at 3 GHz. The external modulation source (from the BNC output of another SRS SG384) is a 5 kHz, 1 Vpp sine, pulse modulated with a 50% duty cycle at 1 kHz and applied to the I input only. The DC offsets of the I&Q inputs were adjusted to minimize the carrier feed through during the external modulation “off” time. The external I/Q modulation circuits are the same in both the SRS SG380 series and SRS SG390 series RF signal generators, and so these results are expected to hold for all of these instruments. External I/Q modulation is an option in the SRS SG380 series instruments and a standard feature in the SRS SG390 series instruments.  
Related Products