Mhz Vctcxo; Synthesizer Circuit - Furuno FS-1575 Service Manual

2. 36MHz VCTCXO

The 36-MHz reference oscillator is of the voltage controlled, temperature compensated
type and provides a high level of frequency stability. This oscillator also allows the
control of frequencies with voltage.
Make adjustment of frequency deviation to "±10 Hz" by selecting [MENU] -> 9.
SERVICE -> 3.RT SETUP-> 1.SETUP -> "REF OSC."
used to make reference offset adjustment. Set "REF OSC" to "0," and then make
"R143" adjustment so that the deviation of a frequency of 36 MHz will come to
"±1 Hz." For the procedure for making frequency adjustment, refer to information on
page 5-29.
This reference frequency signal is inputted in the PLL circuit of the TX board, and also
outputted to the RX, WR1, and WR2 boards. However, a frequency of 18 MHz, half the
frequency of 36 MHz is outputted to the RX board.
・TX board: 36 MHz (72 MHz (36 MHz multiplied by 2) to the 1st local oscillator)
・RX board: 18 MHz (36 MHz divided by 2)
・WR1 and WR2 boards: 36MHz

3. Synthesizer circuit

A circuit used to output the 2nd oscillation frequency consists of DDS and PLL circuits.
The DDS circuit outputs a frequency of approximately 6 MHz. This frequency is taken
as a reference frequency for the PLL circuit.
The PLL IC (U13) operates in steps of approximately 1 MHz using the "devide-by-6"
R-counter and "devide-by-72 to 103" N-counter in combination.
• DDS output frequency: F
• PLL output frequency: F
Furthermore, in order to expand the VCO oscillation frequency range (72,065.5 kHz
(100 kHz) to 101,965.4 kHz (29,999.9 kHz), the VCO circuit is divided into four bands
and each of the four bands are further divided into two subbands.
Band
1
2
3
4
Note) For USB, add a shift frequency of 1.5 kHz to the oscillation frequencies listed
above. PLL setting shift frequencies are as follows:
CONFIDENTIAL (internal use only)
This confidential document is used only by FURUNO authorized persons.
It is strictly prohibited to reproduce the document in whole or in part without prior written permission of FURUNO.
= (Lo / N) × R
DDS
= (N / R) × F
VCO
H/L 2nd Lo Output Freq.
L 73560.0 to 74963.9kHz
H 74964.0 to 78163.9kHz
L 78164.0 to 81663.9kHz
H 81664.0 to 85363.9kHz
L 85364.0 to 89263.9kHz
H 89264.0 to 93363.9kHz
L 93364.0 to 97563.9kHz
H 97564.0 to 99436.0kHz
• USB: +1.5 kHz
・H3E, CW, TLX: 0 kHz
7-11
"R143" is a variable resistor
REF
Table 7.2.2 Division of 2nd Lo Frequency
Setting Freq.
1.605-3MHz
3-6.2MHz
6.2-9.7MHz
9.7-13.4MHz
13.4-17.3MHz
17.3-21.4MHz
21.4-25.6MHz
25.6-27.5MHz
7.2 Transmission Circuit