LimeRFE

An RF Front End Module for the LimeSDR Platforms

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A Complete Solution for Custom HAM, Cellular, and Wideband Networks

The Lime RF Front End (LimeRFE) is a power amplifier (PA) module with appropriate filtering and support circuity to augment the LimeSDR, LimeSDR Mini, and LimeNET Micro platforms to form a complete solution to address real life applications, ranging from HAM radio to standards-compliant cellular network implementations.

Software-defined Front End

A single LimeRFE covers three very different sets of bands: HAM, cellular, and wideband. The exact band used at any given time is software-selectable. By making the RF front end definable in software, LimeRFE is the next step in the evolution of software-defined radio.

LimeRFE render front (left) and back (right)

Features & Specifications

HAM Bands

No. Name Frequency (MHz) Output P1dB (dBm)*
1** HF** 1.6 – 30** 35
2 2 m 144 – 146 36
3 70 cm 430 – 440 34.5
4 23 cm 1240 – 1325 30.5
5 13 cm 2300 – 2450 33.5
6 - 3300 – 3500 26.5

* Preliminary estimates of 1-dB compression point

** See note below about HF bands

A Note About HF Bands

Depending upon the application and overall system configuration, additional filtering may be required for use with HF bands. In particular, HF is not one, but ten bands starting at 1.6 - 1.8 MHz and moving up incrementally to 28.0 - 29.7 MHz. On-board filtering will attenuate signals greater than 30 MHz, but not Tx harmonics, or out-of-band Rx signals below this. Whether you need additional filtering could depend on things like use of external power amplifiers with integrated filters, antenna tuning units, and the environment (e.g., presence of nearby HAMs operating on other HF bands).

Cellular Bands

No. Name Duplex Downlink Freq. (MHz) Uplink Freq. (MHz) Modulated Output Power (dBm)
1 Band 3/DCS-1800 FDD 1805 – 1880 1710 – 1785 24
2 Band 2/PCS-1900 FDD 1930 – 1990 1850 – 1910 24
3 Band 1 FDD 2110 – 2170 1920 – 1980 24
4 Band 7 FDD 2620 – 2690 2500 – 2570 24
5 Band 38 TDD 2570 – 2620 2570 – 2620 24

Wideband Channels

No. Frequency (MHz) Output P1dB (dBm)*
1 1 – 1000 27.5
2 1000 – 4000 25.5

* Preliminary estimates of 1-dB compression point

  • Filtering
    • Each band has appropriate filtering both for RX & TX
    • Selectable AM/FM notch filter
  • Fully Open Source Software
    • Firmware
    • API support
    • GUI
    • LimeSuite integration
  • Control & Configuration
    • Programmable via Arduino IDE
    • Arduino Nano-compatible microcontroller (ATmega328)
    • FT232RL USB-to-serial converter
    • Host serial connection via USB mini Type B connector
  • Power & SWR Meter
    • 1 – 4000 MHz power & SWR meter (external directional coupler required)
    • Cellular bands TX power meter (internal coupler)
  • 10-pin Interface to SDR
    • Power and ground
    • I2C (SDA and SCL)
    • 2x GPIO connected to on-board microcontroller
    • 4x bi-directional level shifted I/O
      • 1.2 – 5.5 V
      • Each I/O has a high voltage and power Darlington drive stage for inductive loads (e.g., coaxial relays)
      • Individually switchable direction (input/output)
  • Power Supply
    • Single 12 V supply
    • Optionally supply microcontroller and RX channels via USB

Block Diagram

* Output 1 dB compression values are preliminary assessments only. Final values may differ. Values are given for the driver outputs - final output values will be lower.

Development Status

We’ve produced a number of prototype revisions to verify the performance over the frequencies and bands of detailed above. We are close to finalizing the board and will be launching the campaign very soon.

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