User's Manual

MaxonSM5102Radio
Level Shifter & Charge Pump
The charge pump is used for changing output signals Fr, Fv at PLL IC from 0-5v to 16v necessary for controlling vco.
DC to DC Converter
The DC to DC converter converts the 8v to 15-16v to supply the necessary voltage for wide range frequency in vco.
VCO
The TX and RX VCO generates RF carrier and local frequency and each VCO is switched by a TX/RX power source. It
is configured as a Colpitts oscillator and connected to the buffer as a cascade, the bias circuit is a cascade configuration
to save power. The varicap diode D201/D202 are low-resistance elements and have different capacitance for reverse
bias voltage.
Using the change of reverse bias voltage(2v – 14v), the wanted frequency for each channel can be obtained.
L203 are resonant coils and L303 are used to change the control voltage by the tunning core.
D201 modulation diode modulates the audio signal. C208,C308 compensates the non-linearity of the VCO due to the
VCO due to the modulation diode and maintains a constant modulation regardless of frequency.
Microphone Audio Circuit
Microphone audio is fed through the front panel PCB onto the main PCB, where it is amplified, pre-
emphasised and limited before being applied to the VCO and TCXO (via pin 1 on TCXO module).
Frequency synthesiser circuit
With data received from the EEPROM (U6) the frequency synthesiser circuit controls and produces the RF
carrier frequency for the transmitter during transmit and the local oscillator frequency for the receiver. The
frequency synthesiser circuit is comprised of:
• Rx/Tx Voltage Controlled Oscillator (VCO)
• Charge Pump and Loop Filter
• Dual Modulus Prescaler
Voltage Controlled Oscillator
Contains two VCOs. One for producing carrier frequencies during transmit and one for producing the
local oscillator frequency during receive. The module also has Rx and Tx power line filters.
RX/TX VCO
The VCO consist of an RX VCO and a TX VCO. It is switched RX/TX by the power source .
It is connected to the buffer as a cascade bise in order to save power . The varicap diode
D201,D202,D301 are low-resistance elements and produce a change in frequency With a change in
reverse bias voltage(1.5~11v) .L203,L303 are resonant coils,which change the control voltage by the
tuning core. D201modulation diode, modulates the audio signal.
Charge Pump and Loop Filter
Transistors Q903 to Q904 and associated resistors and capacitors form the charge pump and loop
filter. The phase detector output from U1 pins 7 and 8 are combined by the charge pump to produce a
0 – 16 tuning volt signal. The signal is filtered by the loop filter to remove any residual reference
frequency harmonics from the signal. After filtering, the signal is applied to the voltage controlled
oscillator module.
Dual Modulus Prescaler
The prescaler divides the VCO frequency by 64 or 65.