Table of Contents
Advertisement
DC TO DC CONVERTER
The DC to DC converter converts 5v to 14-16v to supply the necessary voltage for wide range
frequency in the VCO.
VCO
The radio adopts a two VCO system for RX and TX in order to maximize each performance.
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/D301are low-resistance elements and have different capacitance for reverse bias voltage.
Using the change of reverse bias voltage (2 ~ 11V), the wanted frequency for each channel can
be obtained. L203/L303 are resonant coils and C208/C308 are used to change the control
voltage by the tuning core. D202 modulation diode modulates the audio signal. C204
compensates the non-linearity of the VCO due to the modulation diode and maintains a
constant modulation regardless of frequency.
4.3.2. TRANSMITTER
The transmitter consists of:
1. Buffer
2. P.A. Module
3. Low Pass Filter
4. Antenna Switch
5. A.C.C. Circuits
BUFFER
VCO output level is -4dBm and amplified to +10dBm. The buffer consists of Q9 and Q10 for
reverse isolation and gain.
P.A. BLOCK
The P.A. Block uses a three stage amplifier and contains Q501, Q502, and Q503. The SD-171,
SD-174 have different amplifiers applied compared to the SD-161, SD-164 because different of
a output power specification. Q501 amplifies the TX signal from +10 dBm to 100mW and Q502
28
Advertisement
Table of Contents
