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Page: 17 Of 57
Model No: 3420
Drawing No:
Customer :
Model No:
H 520 PLUS
Rev. Date:
2. BASIC SYNTHESIZER SCHEME
The crystal frequency (10.240MHz) is divided by 1800 times to make 2.5 KHz which is fed to one side of the
phase detector. The VCO output is divided by a programmable divider, and fed to other side of the phase
detector Pin 11 of IC302. The feedback loop is closed by passing the phase detector output through an active low
pass filter and using the output to control the VCO frequency through varicap diode D301.
Under locked conditions, both of phase detector input signal must be indential at 2.5 KHz. The VCO frequency is
then given by:
FVCO / N = 0.0025 MHz or FVCO = 0.0025 x N MHz
Since “N” is an integer, the VCO frequency can be stepped up with 2.5 KHz increments. By suitable choice of “N”
the desired output frequency can be obtained.
Channel 1
Channel 40
N
FVCO
N
FVCO
Function
Transmit 5393
13.4825
5481
13.7025
Receive 6508
16.2700
6684
16.7100
EU
Transmit 5520.25
13.800625
5598.25
13.995625
Receive 6762.50
16.90625
6918.5
17.29625
UK
(SEE TABLE FOR OTHER CHANNELS)
