## RXM-GPS-R4 Overview The **RXM-GPS-R4** is a high-performance GPS receiver module developed by Linx Technologies (now part of TE Connectivity). It belongs to the **R4 Series**, designed for low power consumption and high sensitivity in positioning applications. ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Receiver Type** | 66-channel MediaTek MT3339 Engine | | **Sensitivity** | -165 dBm (Tracking), -148 dBm (Cold Start) | | **Update Rate** | 1Hz to 10Hz | | **Supply Voltage** | 3.0V to 4.3V | | **Operating Current** | 18mA (Tracking), 20mA (Acquisition) | | **Protocol** | NMEA-0183 (Default), PMTK (Command sets) | | **Interface** | UART (Universal Asynchronous Receiver-Transmitter) | --- ### 2. Core Electronic Components & Architecture The module is a "System-in-Package" (SiP) that integrates several critical electronic sub-systems: #### A. The MediaTek MT3339 Chipset The heart of the module is the **MT3339** baseband processor. This chip handles the complex mathematics required to calculate Time of Flight (ToF) from satellite signals and translates them into latitude, longitude, and altitude data. #### B. Internal Low Noise Amplifier (LNA) To achieve its high sensitivity of -165 dBm, the module includes a built-in LNA. This boosts the extremely weak signals received from satellites before they are processed, allowing the module to work even in dense urban environments or under light foliage. #### C. SAW Filter Surface Acoustic Wave (SAW) filters are integrated to reject interference from nearby cellular or Wi-Fi signals. This ensures that only the GPS L1 frequency (1575.42 MHz) is passed to the processor. #### D. TCXO (Temperature Compensated Crystal Oscillator) Because GPS timing requires extreme precision (nanosecond level), a standard crystal is insufficient. The R4 uses a **TCXO** to maintain a stable clock frequency regardless of temperature fluctuations, which significantly speeds up the "Time to First Fix" (TTFF). --- ### 3. Pin Configuration & Hardware Integration The module is designed for surface mount (SMD) integration. Below are the primary pins used in a circuit: ```c // Example Pin Logic for Hardware Integration Pin 1 (VCC): Power supply (3.3V typical) Pin 2 (GND): Common ground Pin 3 (TX): Serial data output (NMEA sentences) Pin 4 (RX): Serial data input (Configuration commands) Pin 10 (RESET): Active low reset Pin 12 (1PPS): 1 Pulse-Per-Second output (High precision timing) ``` --- ### 4. Implementation Requirements To use the RXM-GPS-R4 in a custom PCB, the following peripheral components are typically required: * **Antenna:** A passive or active 50-ohm antenna. * **Backup Battery:** A small coin cell or supercapacitor connected to the `VBACKUP` pin to retain satellite data (Ephemeris) for faster warm starts. * **Decoupling Capacitors:** 10µF and 0.1µF capacitors on the VCC line to filter power supply noise.