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3-45
Vector modulation mode
Vector modulation
In vector mode operation the instrument provides IQ modulation of the carrier from an external
source. The RF level can be varied by applying an envelope control voltage. Fading errors can be
simulated. Provision is also made for using an external mixer to generate a modulated carrier at a
higher frequency than can be provided by the instrument.
To select the Vector control function press the
[Vector]
key on the
Modulation Mode Selection
Menu
(see Fig. 3-6), followed by [SIG GEN]. This causes the
Sig Gen
menu shown in Fig. 3-45
to be displayed.
Sideband : UPPER
IF
: 132 MHz
Envelope : DISABLED
RF
Level
Carrier
Freq.
LOCAL
Config.
Select
IQ
Selfcal
Carrier :
Freq.
RF Level :
dBm
Vector Mod’n Mode
Modulation ENABLED
MHz
Int Std: 10 MHz
2 700.000 0000
-138.0
ON
C1627
Fig. 3-45 Sig Gen menu in vector modulation mode
Setting the output carrier
In vector modulation mode the carrier output frequency and level are set by pressing the
[Carrier
Freq.]
and
[RF Level]
keys respectively and entering the values in the normal way.
Self-calibration
To achieve the high precision of the complex modulation the 2050T series Signal Generators have
an IQ self-calibration feature which automatically adjusts the modulator for optimum performance
minimising vector errors. The instrument generates a warning message at the top of the screen
when an IQ self-calibration is advisable. This will occur 30 minutes after power-on and thereafter
at 3 hour intervals.
To perform a self-calibration press
[IQ Selfcal]
. The calibration process is automatic and during
operation the message
IQ MODULATOR CALIBRATION IN PROGRESS PLEASE WAIT ...
appears.