Synthesizer - Aeroflex NAV 2000R Operation Manual

Aeroflex Operation Manual

4.3.13 SYNTHESIZER

The synthesizer module consists of the REFERENCE/CONTROL board, the RF/OUTPUT board, the
MAIN VCO board, and the 400 MHz VCO board. A block diagram of the module (JPN 40-9520-52) is
located in Section V of this manual.
Referring to this block diagram, frequency generation begins with the 10 MHz Temperature Compensated
Voltage Controlled crystal Oscillator. The output of this frequency standard is buffered and sent
throughout the REF/CONTROL board, and to the RF/OUTPUT board as the reference for the 400 MHz
phase lock loop. Within the REF/CONTROL board, this 10 MHz is transformer coupled to the TIME
BASE, 10 MHz OUTPUT jack, buffered and sent to a 10 MHz phase detector, buffered and sent to the
microprocessor and Direct Digital Frequency Synthesizer circuitry, and buffered and sent to the mixer
circuit.
The 10 MHz sent to the reference phase detector, allows an external 10 MHz reference to be used as the
frequency standard. A signal sensed at the 10 MHz INPUT causes the output of the Low Passed filtered
phase detector to be applied to the voltage control of the TCVCXO, thereby phase locking the internal
standard (TCVCXO) to the externally applied reference signal.
The 10 MHz is used by the microprocessor and direct digital frequency synthesizer as basic operating
clocks. The microprocessor interfaces with the NAV 2000R system buss and generates the control
signals required to program and monitor frequency generation. The Direct Digital Frequency Synthesizer
clocks into the Digital to Analog Converter values at a 10 MHz rate that produces a sine wave of 700 kHz
plus or minus 1.2 kHz with millihertz of resolution.
The output of the DAC is passed through a 1 MHz low pass filter and then to a mixer. Here it is mixed
with the 10 MHz to produce 10.7 MHz plus or minus 1.2 kHz. The filtered output of the mixer
is passed to the RF/OUTPUT board where it is used as the reference for the MAIN phase lock loop.
The RF/OUTPUT board consists of a MAIN phase lock loop, RF divide by two and divide by four circuits,
harmonic suppression filter networks, 400 MHz phase lock loop, low band mixer, and an output leveling
circuit.
The Main phase lock loop uses a PLL IC which incorporates reference dividers, a dual modules
prescaler, divide by A and N counters , and a digital phase detector. The 10.7 MHz reference from the
REF/CONTROL board, is divided by 214 to produce an internal 50 kHz reference for the phase detector.
The Main VCO output is divided by, the divide by 64/65 prescaler, and the A and N counters. This
produces a total divide ratio of from 4500 to 9125, thus the VCO frequency produced will vary from 225
MHz to 456.25 MHz. The 50 kHz phase detector reference allows the PLL to be programmed in 50 kHz
steps. To produce the smaller 10 Hz steps, the 10.7 MHz is skewed up or down. As described
previously, this is done by the Direct Digital Frequency Synthesizer on the REF/CONTROL board.
The Main Loop is only required to produce a frequency range of 225 MHz to 456.25 MHz for the NAV
2000R synthesizer to generate output frequencies of 150 kHz to 450 MHz. For output frequencies of 225
MHz to 450 MHz, the Main Loop output is used directly. For output frequencies from 112.5 MHz to 225
MHz, the Main Loop output is divided by two. For output frequencies of 56.25 MHz to 112.5 MHz, the
Main Loop output is divided by four. To produce the Low Band range of 150 kHz to 56.25 MHz the Main
Loop output is mixed with a fixed 400 MHz.
NAV 2000R SIGNAL GENERATOR - REV. 0 – JULY 26, 2007 - PG 4-10