Anritsu 682XXB - Manual (Page 40)

output signal sample with the adjacent coarse-loop
harmonic produces a low frequency difference signal
that is the YIG IF signal (21.5 to 40 MHz).
The 682XXB/683XXB CPU programs the coarse-loop
oscillator’s output frequency so that one of its har-
monics will be within 21.5 to 40 MHz of the desired
YIG-tuned oscillator’s output frequency. The YIG
Loop phase detector compares the YIG IF signal to
the 21.5 to 40 MHz frequency reference signal from
the Fine Loop. If there is a difference, the YIG phase
detector fine tunes the YIG-tuned oscillator (via the
FM circuitry and the FM coil driver) to eliminate
any frequency difference between the two signals.
Phase locking the instrument’s output frequency
over a broad frequency range is accomplished by
programming the coarse-loop oscillator’s output to
various frequencies that have harmonics close to the
desired operating frequencies. Exact frequency tun-
ing for each desired operating frequency is accom-
plished by programming the fine-loop oscillator. (In
each case, the YIG-tuned oscillator is first tuned via
the main tuning coil to the approximate desired op-
erating frequency.) Table 2-1 shows the coarse-loop
and fine-loop frequencies for some specific RF out-
put frequencies.
The coarse-loop oscillator has a programming (tun-
ing) range of 219.5 to 245 MHz and a resolution of
1 MHz. This provides harmonics from
³1.9755 GHz
to >20 GHz. This allows any YIG-tuned oscillator
output frequency to be down converted to a YIG IF
signal of 21.5 to 40 MHz.
The YIG Loop is fine tuned by varying the 21.5 to
40 MHz reference frequency signal applied to the
YIG loop phase detector. By programming the fine-
loop oscillator, this signal can be adjusted in 1 kHz
increments over the 21.5 to 40 MHz range. The reso-
lution of the fine-loop oscillator (hence the resolu-
tion of the RF output signal) is 1 kHz, which is
much finer than is available from the coarse loop
alone. For applications requiring a resolution finer
than 1 kHz, an optional tuning resolution of 0.1 Hz
is available.
The Coarse Loop and Fine Loop outputs are derived
from high-stability 10 MHz and 500 MHz signals
generated by the Reference Loop. For applications
2-12 682XXB/683XXB MM
FUNCTIONAL FREQUENCY
DESCRIPTION SYNTHESIS
RF OUTPUT/LOOP FREQUENCIES
(in MHz)
RF OUT COARSE LOOP FINE LOOP
2000 219.5 24.5
3000 229 23
4000 234 22
5000 237 23
6000 239 25
7000 240.5 25.5
8000 241.5 30.5
9000 242.5 27.5
10000 243 37
11000 238.5 29
12000 239.5 25
Table 2-1. RF Output and Loop Frequencies