Learning About LMR SDR V1.7 15 Watt
The LMR SDR V1.7 is a multiband software-defined transceiver designed by YE3CIF. Its major upgrade from earlier iterations is the integration of a 15-watt power amplifier directly onto the main board, eliminating the need for separate exciter and PA modules.
Here are the technical highlights of the V1.7 design:
- Final Stage: It uses two RD15HVF1 MOSFETs to deliver a steady 15 to 20 watts of RF output evenly across all bands.
- Bias and Idle Current: The bias voltage at the transistor gates is tuned to approximately 4 Volts. This establishes an idle current of around 500mA to maintain linear operation.
- RF Transformer:To achieve this power, the later revisions (late 2023) swapped the older bifilar transformer for a trifilar design, specifically winding 4-10 turns of 0.5mm enameled wire on a 10mm toroid core. This change was implemented to ensure the 15 to 20-watt output remains consistent across all HF bands.
- Software & Firmware:The STM32 microcontroller firmware remains identical to version 1.6, and the radio continues to interface seamlessly with PowerSDR.
- Enclosure:The PCB dimensions were specifically calculated to drop directly into standard commercial aluminum project boxes, meaning the front and rear panels just need standard drilling.
With 15 watts of baseline output, this board provides more than enough drive power to directly key up a larger 100W linear amplifier—such as a VU2EVQ design—completely bypassing the need to homebrew an intermediate QRP driver stage.
The official Bill of Materials (BOM) and component lists for the LMR SDR Version 1.7 are available for download on the ORARI Malang Raya LMR SDR v1.7 BOM Archive.
Complete Layout & Component Guides: You can access structured, itemized part layouts from the developer’s community portal on the Scribd LMR SDR V1.7 BOM Document.
Full Device Schematic: If you prefer tracing the circuit layout manually while sourcing parts, download the full blueprint at the Scribd LMR SDR V1.7 Schematic Design Sheet.
Key Components to Highlight
| Section | Key Components / ICs | Purpose |
|---|---|---|
| Main Processing | STM32F103C8T6 (Bluepill Module) | Acts as the core microcontroller system logic. |
| Frequency Synthesizer | Si5351A-B-GT + 27.000 MHz TCXO | Manages stable clock generation and variable frequency control (VFO/BFO). |
| Power Amplifier | 2x RD15HVF1 (or RD16HHF1) RF Transistors | Delivers the integrated 15-watt linear transmission output. |
| Mixer & Switches | FST3253MX Bus Multiplexer | Drives high-speed QSD/QSE processing for RX/TX mixing. |
| Audio Processing | NE5532 & TL084IDR Operational Amplifiers | Amplifies baseband input and line-level audio outputs. |
| Voltage Regulation | AMS1117-5.0, AMS1117-3.3, and 7812 | Step downs power rails smoothly across 13.8V input. |
| Toroids & Chokes | BN43-3312 (for linear output transformer) | Crucial for winding custom RF inductors and transformers. |