LORA Frequency hopping, Max Transmit power and FCC Rules

Hello,
I have few questions that will help any non RF person planning to use lora and be compliant with FCC rules. Any help will be appreciated.

  1. As I read on LoRa FCC Certification Guide and 47 CFR § 15.247 - Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz. | CFR | US Law | LII / Legal Information Institute frequency hopping is required to use license free band in order to evenly distribute traffic among channels. Does that mean using single channel modules like RFM95W are illegal to use?

  2. Most of the use cases and libraries I came across for RFM95W are using it as single channel transmitter/receiver at fixed spread factor. Anyone has tried to implement frequency hopping algorithms? I think HOPE RF hardware (SX1276) itself supports frequency hopping as mentioned in datasheet.

  3. Adafruit #4327 is a 8 channel Lora gateway. But as mentioned in LoRa FCC Certification Guide you need to use at least 25 channels equally to transmit data to be compliant with FCC Part 15.247(a)(1)(i). Maybe I am interpreting something incorrectly.

  4. If transmission has to be equally distributed among X channels and receiver has to actively listening for same channel, how can you listen all frequency simultaneously with software/hardware frequency hopping.

  5. What is Maximum allowed Transmit power for license free use (with 2 dbi antenna)? If I increase antenna gain at what promotion transmit power has to be reduced?

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The RFM 95 / SX1276 is a single channel at a time but that does not mean that you are confined to only operating it on one channel.

Most of the use cases and libraries I came across for RFM95W are using it as single channel transmitter/receiver at fixed spread factor.

Those are primitive and not practically usable demos of the LoRa radio alone. They are not LoRaWan, and as such they are not compatible with TTN and not on topic here.

as mentioned in LoRa FCC Certification Guide you need to use at least 25 channels

Read further until you get to the discussion of hybrid schemes

ransmission has to be equally distributed among X channels and receiver has to actively listening for same channel, how can you listen all frequency simultaneously with software/hardware frequency hopping.

This is why LoRaWan requires a multi-channel concentrator chip in a gateway, not a one-channel-at-a-time node class radio which simply cannot fill that role.

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If you want to form a reference for FCC compliant use of plain LoRa, a better place would be over in the Semtech developer forums, where use of the LoRa devices in plain point to point mode would be supported.

If you are getting started with LoRaWAN, that’s great, on this forum we do LoRaWAN on TTN. This is a standard that when you use one of the radio modules or common software stacks will cover the compliance issues for you. Reading some or all of this may help:

Read all of: https://www.thethingsnetwork.org/docs/lorawan/
The devices section of: https://www.thethingsnetwork.org/docs/devices/
The gateways section of: https://www.thethingsnetwork.org/docs/gateways/
The network section of: https://www.thethingsnetwork.org/docs/network/
The applications and API sections of: https://www.thethingsnetwork.org/docs/applications/

Yes, We are planning to deploy LoRaWAN on TTN. TTN fundamentals are clear to me but I need more info on RF side. I would like to maximize the range while being FCC compliant.

The decision to use TTN removes most of it from your control, since both the gateway transmit power, and (if you use ADR, which you probably should) node transmit power are commanded by the network.

You can of course rig things to output less power than commanded if you feel that’s appopriate.

Mostly though you’re left with duty cycle. IIRC the regs you face may be written more in terms of packet duration limit, which does place a fairly short limit on what you can do at SF10 (and make anything slower unusuable) compared to the very long and slow packets that European TTN users are used to.

Understood. How about Antenna Gain / Directional antenna? Any restrictions on using higher gain antenna?

Did you look?

If you did, you’d see that you’re supposed to factor that into the calibration tables that your nodes and gateway use to achieve the commanded radiated power.

If you looked here on the forum you’d also see that directional antennas are not recommended.

The only place they might barely make sense would be on a node if you knew where the gateway was, since while it wouldn’t get you any more radiated power, it could let you achieve the radiated power at a lower battery cost.

Do you have a couple of gateways and half-a-dozen devices going yet?

If not, I’d get to that point before trying to warp time & space. There’s plenty to learn before then and you can engineer a truly Evil Genius scheme for your long distance antenna array only to find the local concrete manufacturer’s trucks passing back and forth on the highway scuppers the whole deal.