2-8
SYN circuit
2Lo2Lo
2Lo2Lo
2Lo
Mixing at Q510 the frequency of the 36MHz reference oscillator and the output of “18MHz” dividing
the frequency 1/2 by U505, 2nd local oscillator generates 54MHz.
3Lo3Lo
3Lo3Lo
3Lo
3Lo is generated by the DDS, U506 and FL503 (455kHz, BPF) at the next stage.
Phase data is set from the main CPU to the DDS, and the signal of “456.7kHz” is output.
The phase data is shown by the formula below:
Phase data : K = (2
n
/ DDS CLK) x DDS F
OUT
= 108972865
n : Phase accumulator bit count of DDS = 32 bits
DDS CLK : 18,000,000Hz
DDS F
OUT
: 456,700Hz
1Lo1Lo
1Lo1Lo
1Lo
1Lo is the PLL circuit consisting of U501, DDS and U502, VCO generates the signal “F+54.455MHz”
The DDS output frequency, about 6MHz is set to the PLL reference frequency, and frequency dividing
ratio of the PLL and reference frequency from the DDS are set according to preset frequency informa-
tion, by there generating required frequency.
Relation between DDS and PLL oscillation frequency is:
- DDS output frequency : fo = (K x fc) / 2
n
fc : DDS CLK (18MHz)
n : DDS phase accumulator bit count (32 bits)
K : DDS phase data input (Frequency data of 32 bits from CPU)
- PLL oscillation frequency : 1Lo = (fo x N) / M
Comparison frequency divider : N (54 to 84) (frequency data from CPU)
Reference frequency divider : M (Fixed at 6)
The PLL (VCO) oscillates between 56.0615MHz and 81.955MHz with setting frequencies of
1.6065MHz to 27.5MHz. The oscillation frequency range of 30MHz approximately cannot cover by a
single VCO. For that reason, the oscillation coil of the VCO circuit is divided by 4 according to setting
frequency, each of which is further divided by 2 to generate 1Lo. Setting frequency versas VCO output
frequency is tabulated below.
3. Function and overview of each board
BAND Setting Freq. VCO Output Freq.
1-L 1.6065 - 2.99999 MHz 56.06150 - 57.45499 MHz
1-H 3.0 - 5.99999 MHz 57.45500 - 60.45499 MHz
2-L 6.0 - 9.49999 MHz 60.45500 - 63.95499 MHz
2-H 9.5 - 13.49999 MHz 63.95500 - 67.95499 MHz
3-L 13.5 - 17.49999 MHz 67.95500 - 71.95499 MHz
3-H 17.5 - 21.49999 MHz 71.95500 - 75.95499 MHz
4-L 21.5 - 25.49999 MHz 75.95500 - 79.95499 MHz
4-H 25.5 - 27.50000 MHz 79.95500 - 81.95500 MHz
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