Anritsu 682XXB, 683XXB manual MHz, RF OUT Coarse Loop Fine Loop

FUNCTIONAL	FREQUENCY
DESCRIPTION	SYNTHESIS

Table 2-1.RF Output and Loop Frequencies

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

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 ￿1.9755 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

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