The **XT09-PKI-R** is a legacy high-performance 900 MHz stand-alone radio modem produced by Digi International (formerly MaxStream). It is designed for long-range serial communication in industrial environments. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Frequency Range** | 902 - 928 MHz (ISM Band) | | **Power Output** | 1 mW to 100 mW (Variable) | | **Indoor Range** | Up to 1500 ft (450 m) | | **Outdoor Range** | Up to 20 miles (32 km) with high-gain antenna | | **Interface** | RS-232 / RS-485 (DB-9 Port) | | **Data Rate** | 9.6 kbps or 19.2 kbps | | **Modulation** | Frequency Hopping Spread Spectrum (FHSS) | --- ### 2. Core Electronic Components The XT09-PKI-R is an assembly consisting of an internal RF module housed in a rugged enclosure with interface circuitry. #### A. The RF Module (9XTend) The heart of the device is the **9XTend (XT09)** OEM module. - **Microcontroller:** Manages the FHSS algorithms and packet framing. - **Transceiver IC:** Handles the modulation/demodulation of the 900 MHz signal. - **Power Amplifier (PA):** Boosts the signal up to 20 dBm (100 mW) for long-range transmission. #### B. The Interface Board (PKI) The "PKI" designation refers to the RS-232/485 interface board. - **RS-232/485 Transceivers:** ICs (like the MAX232 or similar) convert standard PC-level serial signals to TTL levels for the RF module. - **Voltage Regulator:** Accepts a wide input range (typically 7-18V DC) and steps it down to the 5V or 3.3V required by the internal electronics. - **Status LEDs:** Indicators for Power (Green), TX (Red), and RX (Yellow). --- ### 3. Connection Pinout (DB-9) The device typically uses a standard DB-9 female connector. Below is the typical RS-232 configuration: | Pin Number | Signal Name | Direction | | :--- | :--- | :--- | | 2 | TXD | Output (to PC) | | 3 | RXD | Input (from PC) | | 5 | GND | Ground | | 7 | CTS | Output (Clear to Send) | | 8 | RTS | Input (Ready to Send) | --- ### 4. Operational Features 1. **FHSS Technology:** It hops between frequencies within the 900MHz band to avoid interference and provide secure data transmission. 2. **Peer-to-Peer & Point-to-Multipoint:** Supports complex network topologies beyond simple cable replacement. 3. **Buffer Management:** Includes internal buffers to handle data flow when the RF link is busy.