Anritsu 682XXB - Manual (Page 42)

Frequency
Modulation Frequency modulation (FM) of the YIG-tuned oscil-
lator RF output is achieved by summing an external
or internal modulating signal into the FM control
path of the YIG loop. Refer to Figures 2-1 and 2-2.
The external modulating signal comes from the
front panel or rear panel
FM IN input; the internal
modulating signal comes from the A8 Function Gen-
erator PCB. Circuits on the A11 FM PCB adjust the
modulating signal for the FM sensitivity selected,
then sum it into the YIG loop FM control path.
There, it frequency modulates the RF output signal
by controlling the YIG-tuned oscillator’s FM (fine
tuning) coil current.
Phase
Modulation
(Option 6) Phase modulation (
FM) of the YIG-tuned oscillator
RF output is achieved by summing an external or
internal modulating signal into the FM control path
of the YIG loop. The external modulating signal
comes from the front panel or rear panel
FM IN/
F
M
IN input; the internal modulating signal comes from
the A8 Function Generator PCB. Circuits on the
A11 FM PCB adjust the modulating signal for the
FM sensitivity selected, convert the modulating sig-
nal to a
FM signal by differentiation, and then sum
it into the YIG loop FM control path. There, it phase
modulates the RF output signal by controlling the
YIG-tuned oscillator’s FM (fine tuning) coil current.
Analog Sweep
Mode
(683XXB only) Broad-band analog frequency sweeps (>100 MHz
wide) of the YIG-tuned oscillator RF output are ac-
complished by applying appropriate analog sweep
ramp signals, generated by the A12 Analog Instruc-
tion PCB, to the YIG-tuned oscillator’s main tuning
coil (via the A13 YIG Driver PCB). In this mode, the
start, stop, and bandswitching frequencies are
phase-lock-corrected during the sweep.
Narrow-band analog frequency sweeps ( £100 MHz
wide) of the YIG-tuned oscillator RF output are ac-
complished by summing appropriate analog sweep
ramp signals, generated by the A12 Analog Instruc-
tion PCB, into the YIG-tuned oscillator’s FM tuning
coil control path. The YIG-tuned oscillator’s RF out-
put is then swept about a center frequency. The cen-
ter frequency is set by applying a tuning signal (also
from the A12 PCB) to the YIG-tuned oscillator’s
main tuning coil (via the A13 YIG Driver PCB). In
this mode, YIG loop phase locking is disabled except
during center frequency correction, which occurs
during sweep retrace.
2-14 682XXB/683XXB MM
FUNCTIONAL FREQUENCY
DESCRIPTION SYNTHESIS
NOTE
For 683X5B models at frequencies
of
£2.2 GHz, broad-band analog fre-
quency sweeps are >25 MHz wide;
narrow-band analog frequency
sweeps are
£25 MHz.