8
$\begingroup$

I am very new to general RF/radio in general other than basic WiFi, but I'm looking at the feasibility and cost of a long range (>200M between nodes, sometimes probably 500+M) in flat terrain, relatively low power (solar + 12V SLA, short term usage) and probably fairly low bandwidth needs (couple of hundred Kbps?), but bi-directional/fully shared. So in starting doing some searches/research, I came across this SX1276 based module (https://www.adafruit.com/product/3072) that's relatively cheap, even if I need it for a few dozen or more nodes.

My concept is to use a fixed mesh, or star mesh topology as the distance between a centrally located node and the furthest away may be as much as 2+ km, possibly 3+. That's long term planning, my first attempt would likely be a handful of nodes perhaps 400m-600m from a central point. The advantage of this area is flat as a pancake, although lots of varying height temporary structures, although the antennas would not be placed very high, 6-10 feet off the ground so they may or may not have perfectly clear line of sight.

Based on my reading of LoRaWAN, it's really designed to be a central star network topology without much bi-directional communication, in general. And LoRa could, in theory, perhaps, do a mesh network but it'd need a non-trivial amount of software layered on top of the transceiver access code.

I did come across https://ieeexplore.ieee.org/document/8048465/ which is very interesting. In my naive reading of it, it implies that if you simply immediately re-transmit each packet once received (and ignore it once you've re-transmitted it) you essentially can flood a mesh network of LoRa devices reasonably efficiently despite collisions and such. I did see there's more to it than that with seeing to do offset concurrent transmission and other bits that I didn't get to. If that concept actually works reasonably well, it shouldn't be too difficult, in theory, to put a basic layer on top of a LoRa transceiver to spread data through a mesh (that doesn't actually know about each other really) in an easy to implement fashion which spans several square kilometers.

So...disabuse me of this and show me how naive and unknowing I am and I should tuck my tail between my legs and run away :)

Improve this question
$\endgroup$
6
  • 1
    $\begingroup$ Hi! So, this looks like an interesting engineering problem. However, it's neither about the basic radio principles nor about a ham-specific technology; it's specificically impossible to use this in a ham radio context. As such, I think this is off-topic here, but could fit nicely on electronics.stackexchange.com $\endgroup$
    – Marcus Müller
    Jun 8, 2018 at 8:51
  • 1
    $\begingroup$ I agree with Marcus - this looks really interesting (I am studying LoRa at work ATM) and the brute-force Mesh idea is cool. But it's not ham radio. Please note just HOW low the data rate is of LoRa. If the nodes are all busy retransmitting others' data, the problem gets worse. $\endgroup$
    – mike65535
    Jun 8, 2018 at 16:21
  • $\begingroup$ Ah, didn't know LoRa would be considered other. Actually, honestly, I just searched all the Exchanges for the word "radio", and this popped up :) I'll re-post onto the electronics as suggested by Marcus. Thanks! Or, mike65535, if you want we could take it elsewhere off Exchange if you've got some good ideas for me. $\endgroup$
    – Drizzt321
    Jun 8, 2018 at 17:39
  • $\begingroup$ @MarcusMüller It might be off topic. Although I don't know anything about LoRa, if it's about the technology of radio then it's often --but not always-- allowed here even if it has nothing to do with amateur radio. Having said that, here are the official rules. I'll let Kevin, Scott, and others help decide whether it is or not. $\endgroup$
    – Mike Waters ♦
    Jun 8, 2018 at 20:45
  • 1
    $\begingroup$ Ham LoRa does exist. On the one hand there's not a ton of it, on the other hand, that very lack is a reason to encourage more discussion of it in my opinion, as long as what we learn is applicable to amateur use. $\endgroup$
    – hobbs - KC2G
    Jun 9, 2018 at 2:31

4 Answers 4

Reset to default
2
$\begingroup$

A few comments on amateur LoRa:

  • As others have pointed out, the datarate is measured in tens of bytes per second. Not thousands... Forget about file transfer!

  • LoRa is spread-spectrum and therefore can be used on the 1.25m-band and shorter, with maximum 25W PEP.

  • Enhanced propagation at 1.25m (versus 33cm where LoRa is typically used) opens up exciting possibilities of range. I would expect range similar to a well-equipped 2m SSB/CW station.

  • LoRa is a modulation scheme (analogous to FM), while LoRaWAN is a protocol and topology (analogous to an analog Echolink repeater system).

  • There's a project called "loraham", spearheaded by the hacker Travis Godspeed, which gathered quite a bit of interest. It is a PTP mesh in the spirit of APRS. https://github.com/travisgoodspeed/loraham

Improve this answer
$\endgroup$
2
  • $\begingroup$ Re-thinking it, I was being overly optimistic about total data per message. Assuming limiting the size of a message someone can put in, each message would be hundreds of bytes. Assuming I only handle 1 byte UTF-8 to start with, at a guess 500 bytes? Or maybe even 1 KByte. But, with a limited number of terminals and seconds (or minutes) at minimum between individuals putting in messages, probably can handle it. $\endgroup$
    – Drizzt321
    Oct 31, 2018 at 23:51
  • $\begingroup$ Ohhh, thanks for that link. I wasn't planning on using LoRaWAN, that seemed too centralized for what I wanted. "loraham" seems a lot closer to what I want. In concept at least. $\endgroup$
    – Drizzt321
    Oct 31, 2018 at 23:52
2
$\begingroup$

Ham LoRa does seem to exist, although I haven't seen any mention of it around the Boston MA area.

I think to make best use of LoRa on Ham frequencies, one could use the European version that works in the 70cm band. With that, one could use higher power level (limited by one's local power limits which vary by physical location) and better antennas -- Yagis for fixed, point-to-point service and verticals for multipoint repeater service.

For protocols, one could use something based on UUCICO (the basis of UUCP), the old Unix protocol behind UseNet and mail.

But one ham in a region isn't enough to be interesting.

73, K1UZK (once WA1JMS)

Improve this answer
$\endgroup$
1
$\begingroup$

Let me stress the fact mentioned by @mike65535 again: Couple of hundred kbps is not what LoRa is designed for. It is more in the area of IEEE 802.15.4 (ZigBee etc.) even though you might have to reduce the distance between the nodes a bit depending on the environment and your ability to build good antennas or even amplifiers if you like.

The plus is that there is already well-proven hard- and software available and a lot of existing experience in the area of collision-free data transmission in mesh applications. It is even not very difficult to build your own IEEE 802.15.4 hardware from existing ICs such as the ATmega256RFR2 or the AT86RF23X series.

Finally, since we are talking about ham applications here: It is trivial to use existing IEEE 802.15.4 hardware in the 13 cm ham radio band and I have already done that successfully.

Improve this answer
$\endgroup$
0
$\begingroup$

You might want to take a look at the HC_12 433Mhz devices, they have a range of 1Km. Cheap and dead easy to use. Build your test setup using these units, and iron out your bugs. Then move over to LoRa once you are comfortable that your system is functioning well. Then longer range will be possable.

Improve this answer
$\endgroup$
1
  • $\begingroup$ 433MHz won't work for me, I'm in the US where I believe that's a licensed spectrum, while the 900MHz is what I'd want I believe. $\endgroup$
    – Drizzt321
    Jan 3, 2020 at 0:14

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .