Semtech SX1302 LoRa Transceiver to Deliver Cheaper, More Efficient Gateways

After our interview with Rak Wireless CEO, we received a comment inquiring about the availability of SX1302 gateways. Semtech so far had two LoRa transceivers for gateways namely SX1301 and SX1308, but I had never heard about a third one.

Semtech SX1302 is brand new, the latest generation of baseband LoRa chip for gateways that is said to reduce current consumption in order to simplify the thermal design of gateways, as well as the BoM (bill of materials) costs), while being capable of handling a higher amount of traffic.

Semtech SX1302 LoRa Transceiver

Semtech SX1302

Key features:

  • Up to -141 dBm sensitivity with SX1250 Tx/Rx front-end
  • 125 kHz LoRa reception with:
    • 8 x 8 channels LoRa packet detectors
    • 8 x SF5-SF12 LoRa demodulators
    • 8 x SF5-SF10 LoRa demodulators
  • 125 /250 / 500 kHz LoRa demodulator
  • (G)FSK demodulator
  • Direct interface to Semtech transceivers SX1255, SX1257 and SX1250
  • SPI host interface
  • Single 32 MHz clock
  • QFN68 Package
  • Temperature Range – -40°C to +85°C.

One important change is support SF5 and SF6 high-speed packets that have been made possible by eight extra modems, while the eight others are handling SF7-SF12 traffic. SF stands for Spreading Factor which represents the duration of the transmission.

Semtech SX1250 Front-End

SX1250 front-end

SX1302 is meant to be used paired with SX1250 sub-GHz RF Front End device which covers any frequency band below 1 GHz.

Features:

  • Half Duplex operation
  • Capable of low power operation
  • 150 – 960 MHz ISM frequency bands
    • Europe 868MHz
    • India 866MHz
    • North America 915MHz
    • APAC 920MHz
    • Asia 923MHz
    • Lower UHF bands 169 and 433 or 490MHz
  • Can handle LoRa or FSK
  • Built-in differential Low Noise Amplifier (LNA)
  • Controlled via a serial SPI interface and a set of general-purpose input/output (DIO)

Semtech Corecell SX1302 LoRa Gateway Reference Design

Semtech Corecell SX1302 Gateway

The company has also created a Corecell reference design based on one SX1302 transceiver and two SX1250 RF front-ends, a 27dBm front-end module, and all of the necessary filters and power supplies to create an 8-channel LoRa gateway.

Highlights:

  • 10x power reduction compared to legacy products
  • Maximum TX output power = +27 dBm
  • Receive 8 LoRa channels multi-data rates (SF5 ~ SF12 / 125 Simultaneously kHz) + 2 mono-data rate (LoRa 250 / 500 kHz and FSK 50 kbps)
  • Half Duplex mode
  • Typical sensitivity level:
    • -141 dBm at SF12 BW 125 kHz
    • -127 dBm at SF7 BW 125 kHz
    • -111 dBm at FSK 50 kbps
  • Typical Power Consumption @ 5V
    • 39mA with 8 RX CHANNELS ON and TX OFF
    • 421 mA with 8 RX CHANNELS OFF and TX ON at 27 dBm (868 MHz)
    • 148 mA with 8 RX CHANNELS OFF and TX ON at 14 dBm (868 MHz)
Corecell LoRa Gateway Block Diagram
Corecell SX1302 Gateway Block Diagram – Click to Enlarge

Semtech Corecell is designed for home, building and factory automation. The board interface with the host machine through a mini PCIe interface that requires the following signals:

  • 1x SPI coming from host to the SX1302 SPI interface
  • 1x I2C coming from host to the temperature sensor I2C interface
  • Power Enable line
  • SX1302 reset line
  • PPS ( Pulse-Per-Second) signal

It’s note quite standard so the company also designed an interface board for the mini PCIe card as well as a 40-pin header for easy connect to Raspberry Pi board as shown below.

SX1302 Raspberry Pi Gateway
Click to Enlarge

That also probably means we should shortly see Raspberry Pi-powered SX1302 gateways come to market.

Technical Documentation, and Availability

You’ll find more details including the datasheets on the transceiver, RF front-end, and reference design pages. SX1302 Hardware Abstraction Layer (HAL) and tools such as the packet forwarder can already be found on Github. You may also want to follow the thread about SX132 on TTN forums for new development, or read the comment in this blog post :).

All three are currently listed on Mouser (here and there) with SX1302 going for $18.22 per unit on a 3,000 pieces reel, SX1250 for $2.80, and the Corecell gateway reference design is apparently going for $257.99. Commercial SX1302 gateways will hopefully be more affordable since SX1302, SX1250, and the Corecell gateway are actually slightly cheaper than their SX1308 equivalents.

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dgpzoobabJean-Luc Aufranc (CNXSoft)TLS Recent comment authors
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dgp
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dgp

I wish semtech would put a bit of love into their HAL/forwarder for everyone that already has sx1301s in the wild. Instead of maintaining the existing one and making it compatible with this new chip they’ve copied it and started a new repo.

TLS
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TLS

What’s the difference between APAC (Asia Pacific) and Asia?

zoobab
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I am wondering if a listening-only GW could not be done in software with multiple RTL-SDRs listening each on one channel.

dgp
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dgp

I’ve tried this. In theory you would only need enough SDRs to cover the frequency range and a normal LoRa radio module to act as your transmitter to have a full gateway. In reality the current LoRa block for gnu-radio requires a lot of cpu power so the end result is the hardware to do it in software is going to be multiple times more expensive than just buying an sx130x based concentrator.