DIGITAL MODULATION MODE
3-40
Mixer selection
Pressing the
[Int/Ext Mixer]
key toggles between internal and external mixer selection. When set
to internal mixer the configuration is as shown in Fig. 3-39 where an internal mixer is used to
convert the IQ modulated IF to the required carrier frequency. When external mixer is selected the
normal signal generator output is made available on the RF OUTPUT connector and the
configuration is as shown in Fig. 3-41. The output can then be used as a local oscillator for
external frequency multiplication and mixing with the IF to produce higher frequencies than those
available internally.
When set to internal mixer the IF output is disabled. When set to external mixer the IF
output is enabled and appears at the rear panel IF OUTPUT connector.
IQ
OUTPUT
ENABLE
➤
➤
MODULATOR
DATA
IQ
CHANNEL
FILTER
INTERNAL
DATA
IF
SOURCE
IF
OUTPUT
Q
I
RF
OUTPUT
C1657
ENVELOPE
PULSE
INPUT
EXTERNAL
DATA
2050/1/2
SYNTH
Xn
MODULATED
OUTPUT
Fig. 3-41 Simplified block diagram: Digital mode with external mixing
Pulse input selection (applies if Option 002 fitted)
Pressing the
[Pulse Input]
key enables and disables the pulse input. With pulse input enabled,
applying 5 V to the PULSE INPUT connector turns the RF carrier on and 0 V turns the carrier off.
This facility enables the RF output to be rapidly turned on or off.