4. External modulation
The
QRF
supports external modulation of the
RF
in
NSB
mode through
the modulation input
SMA
connectors on the back-panel. Frequency,
amplitude and phase modulation of the
RF
are supported.
WARNING:
The
modulation
inputs
are
nominally
±
1V,
and
can
be
permanently
damaged
by
applying
higher
voltages.
Disconnected
inputs
are
floating
and
can
cause unexpected results when modulation is enabled.
4.1
Operational principle
Modulation
is
performed
by
digitising
the
analogue
input
signal,
which is then multiplied by the modulation gain and added to the in-
ternal control value associated with the particular modulation mode
(“
frequency tuning word
” for frequency, “
amplitude scale factor
” for
power or “
phase offset word
” for phase). Limits are applied to ensure
that the value remains within the bounds.
The
ADC
has
12-bit
resolution
(
±
1 V
range),
has
2
nd
-order
anti-
aliasing filters at 100 kHz and a measured 3-dB bandwidth of 70 kHz.
Modulation is enabled/disabled with the
MOD
For exam-
ple, to enable
AM
on channel 1, use the command
MOD,1,AM,ON
.
Note
than
no
amplitude-compensation
is
applied
in
FM
mode,
so
changes in amplitude with frequency are expected in applications
that sweep the frequency by a large amount. Consult the test report
shipped with your
QRF
for an indication of the response curve, or
use dual-modulation with
AM
to maintain a desired output power.
Note that modulation is not available in table mode.
1
The “
MDN
” command is a synonym for compatibility with other products.
17
Summary of Contents for QRF041
Page 1: ...Quad RF Synthesizer QRF041 QRF241 Version 0 2 0 Rev 2 hardware ...
Page 4: ...ii ...
Page 10: ...viii Contents ...
Page 12: ...x Getting started ...
Page 16: ...4 Chapter 1 Introduction ...
Page 22: ...10 Chapter 2 Connections and controls ...
Page 28: ...16 Chapter 3 MOGRF host software ...
Page 36: ...24 Chapter 4 External modulation ...
Page 46: ...34 Appendix B Firmware upgrades ...
Page 56: ...44 Appendix C Command language ...
Page 60: ...48 Appendix D Communications ...