ACCEPTANCE TESTING
6-29
Digital modulation mode
IQ outputs
Baseband IQ output signals are available on the front panel at a level of 0.5 V pk PD nominal into
50
Ω
. The following test uses these outputs to provide an operational test of the drive signals for
the IQ modulator in digital mode.
Test equipment
Description Minimum
specification Example
Oscilloscope
2 channel inputs with X-Y facility
Tektronix 2235
C1678
UUT
Q IN/OUT
I IN/OUT
CH 1
CH 2
Oscilloscope
Fig. 6-15 IQ output test set-up
(1) Connect the test equipment as shown in Fig. 6-15.
(2) Set the UUT to Digital Modulation Mode, IQ output enabled, 8PSK modulation and a Nyquist
filter as follows:-
[UTIL]
[Mod’n Mode][Digital]
[SIG GEN]
[Config. Select][IQ O/P Enable]
[SIG GEN]
[Mod’n System][Select Mod. Type][PSK][8PSK]
[EXIT] [EXIT] [Filter Type][Nyquist][EXIT]
[SIG GEN]
(3) Set the oscilloscope to X-Y, channel 1 and channel 2 sensitivities to 0.2 V/div, and check for
8 clearly defined points on the constellation as shown in Fig. 6-16.
Fig. 6-16 8PSK constellation
(4) Set the UUT to generate phase offset
π/4
differential QPSK as follows:-
[Mod’n System][Select Mod. Type][PSK][
π/4
DQPSK]
(5) Check for 8 clearly defined points on the constellation as shown in Fig. 6-17.