30
Chapter 5. External modulation
The
signal
processing
chain
causes
a
propagation
delay
between
the modulation input and the
RF
output of approximately 500 ns in
fast (parallel) mode, and
<
3
µ
s in slow (serial) mode.
Furthermore,
inducing a step change with slow modulation (e.g. using
AM
to switch
the
output)
may
appear
to
have
jitter
of
up
to
500 ns
depending
on the delay between the change in the modulation input and the
subsequent
DDS
update.
Simultaneous
FM
and
PM
is not currently supported, as phase mo-
dulation shares the “
FREQ
” modulation input.
5.4
Examples
5.4.1
Simple linear ramps
Listing 5.1 shows how to use the
MOD OUT
connector on the rear
panel to linearly ramping the
RF
amplitude and frequency simulta-
neously (Figure 5.1).
Ensure that
MOD OUT
is connected to both
the
FREQ1
and
AMPL1
modulation inputs in parallel.
Subsequently
increasing the
AM
gain results in clamping the amplitude to respect
the limit set by the
LIMIT
command (Figure 5.2).
# configure the channel
FREQ,1,60MHz
POW,1,0dBm
LIM,1,10dBm
ON,1
# connect MODOUT to FREQ1 and AMP1 mod in
MOUT,SHLRAMP
MDN,1,AMPL,ON,4000
MDN,1,FREQ,ON,30000
FMSPEED,1,SLOW
Listing 5.1:
Simultaneous
AM
and
FM
Содержание ARF021
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