First, the basic analog walkie-talkie is composed of several key functional modules, including the transmitting module, receiving module, modem module, signaling module, and power control module. These components work together to enable communication over short distances using radio waves.
Second, the core working principles of these modules are as follows:
1. Transmitting Module: The process starts with a phase-locked loop (PLL) and a voltage-controlled oscillator (VCO), which generate the RF carrier signal. This signal is then amplified through buffer, excitation, and power amplifiers to reach the required RF output level. After passing through a low-pass filter to suppress unwanted harmonics, the signal is transmitted via the antenna.
2. Receiving Module: The receiving section typically uses a double-conversion superheterodyne architecture. The incoming signal from the antenna is first filtered and amplified before being mixed with a local oscillator signal from the PLL frequency synthesizer. This generates an intermediate frequency (IF) signal, which is further processed through crystal and ceramic filters to remove interference. After additional amplification and filtering, the signal is converted into an audio signal that is then sent to the speaker through volume control and power amplification circuits.
3. Signaling Processing: Traditional walkie-talkies do not require complex signaling, allowing users to simply tune to a channel and press PTT to communicate. However, modern devices often use CTCSS (Continuous Tone-Coded Squelch System) to filter out unwanted signals. A microcontroller or dedicated chip generates a sub-audio tone, which is modulated onto the RF signal. When receiving, the system checks if the tone matches a preset value; if so, it enables the speaker, otherwise it mutes it.
4. Modulation and Modem Circuit: The user's voice is captured by a microphone and converted into an electrical audio signal. This signal is then amplified, pre-emphasized, and filtered before being directly modulated onto the VCO signal for transmission.
5. Power Control: The CPU manages different power states to optimize energy usage. For example, during reception, the device operates in intermittent mode to save power. Transmission occurs only when needed, while the CPU receives a stable power supply to ensure consistent performance.
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