Meshtastic

Just ordered 10x T-Beams and have a few questions about our network plan

Hi all, I’d love to get your input on this project we’re working on. Most of us involved are new to the radio space, though have a lot of experience with tech and networking in general.

We are far away from power, cellular or anything except evergreen forests and some clearcuts and roads.

We’re hoping to use Meshtastic to connect various camps to at least allow for simple text messages between camps.

Our nodes would be stationary primarily (not hiking :wink: )

We just mapped out a network to connect the various camps, taking advantage where possible of line of sight. And aiming for no more than 5km between nodes, while trying to overcome the 7 hop limit. The network pattern will follow a loose circle pattern with a few zig zags for redundancy and hop reduction.

I’m hoping we can get away with the stock antenna, though I’m open to ordering some of these:

or some directional for the sections that are just daisy chain linking two camps:

Eventually if our first test with these 10 finds some success, the proposed design will have about 20 nodes. With most of our nodes simply straight-line connecting points and set to repeater/router mode.

With the build-in web server, can we use that to overcome the 1:1 relationship between phone and node? So multiple people in a camp can use a node for messaging? Is there any password protection on that web page? (even simple semi-secure is good)

I don’t think the TBeams I ordered come with batteries. (18650 s ?) We were planning to connect the TBeams to external battery packs via usb anyway. Will that work to not use an internal battery and just use an external? If it won’t work, is there any issue with having both internal battery and an external battery pack attached longer term? We’re hoping that we can get at least a few weeks from these before we have to do a looonngg hike through the bush to swap out the external battery packs for charging.

Solar isn’t an option as this is an area that is frequently in low cloud / fog banks.

The frequent fog/cloud/moisture, is one reason we went with 5km between nodes in our map, as 915Mhz may be stopped, even line of sight by water vapour??? I wonder if 5km is even too ambitious.

Can anyone recommend what settings and placements would be optimal for this setup? Like the spread factor? And range/power settings? Antennas? Water vapour range issues?

I’m really hoping that we can get a few nodes into the center of the circle pattern, so it can look more like a mesh and less like a donut, but the logistics around that may mean strapping one to a circling bird …

I’d really appreciate any comments about our proposed setup.

cheers

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It’s 3 hops by default, you’d have to modify the source code and recompile to increase this figure, but that would increase airtime a lot.

Those are car roof antennae; it you’re mainly setting up fixed nodes I’d recommend mast collinears like these (just an example).

Stock antennae aren’t any good, I’d only use them inside the camp on handheld devices which could use the camp’s fixed node as a repeater.

This is a Moxon antenna, it works very well and its forward lobe is very broad, so it’s very easy to aim and you can get a good signal to nodes more than 90° apart!

Eventually if our first test with these 10 finds some success, the proposed design will have about 20 nodes. With most of our nodes simply straight-line connecting points and set to repeater/router mode.

Yes, the only downside is that the T-Beams will not use power-saving, hence battery drain will be much faster.

How bad is it? Please consider that a good panel will produce power ever on a cloudy day. I live in a mostly sunny region and I get get away with a 5 Watt panel charging a 3400 mAh cell, in your case a 30 Watt panel and maybe two cells in parallel could work with a decent safety margin.

Keep in mind that T-Beams have a fatal flaw: when voltage drops low enough, they power off and they do not power back on when voltage rises back above the threshold!

Yes, according to my tests any precipitation negatively affects range, however 5 km in line-of-sight should be almost 100% reliable.

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Thank you, that is very helpful!

When you say < 3 hops will increase airtime a lot, in researching it I’m still not clear on the implications of that. Does that mean the time for a message to be transmitted? Or the amount of time the network is chattering to deliver the message? Or something else?

On that note, I’m wondering how others have worked with or solved the issue of a network spread over a large area. I’m guessing it may be better to optimize transmission (antenna and node placement), rather than simply increasing the number of nodes?

Cost is a pretty big factor here. Those collinear are pricey. If that car roof one has a good ground plane, do you think it could be comparable in performance?

Re: batteries, I didn’t realize how common the 18650s were to buy locally. I was initally looking at ordering from aliexpress. But the local stores here carry them. So we’ll do that. thanks.

Given that fatal flaw with low voltage, you’re right, any solar panel would be better than nothing. I have some 15w that seem to charge fine on cloudy days.

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It means that the radios will collectively spend more time transmitting. One of the (legal) caveat of using ISM bands is that each hour only a certain % of the hour is allowed for transmitting, hence the built-in 3-hop limitation.

That’s certainly a possibility and it’s precisely what we’re trying to do down here in Italy: fixed notes on summits, efficient antennae, etc.

True, they’re very expensive for a conductor with some coils in a plastic tube and some mounting hardware!

A mobile antenna would probably work almost as well, though they usually have a long (hence lossy) cable.

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Re air time and ‘Hops’

You could think of each radio as a person speaking.

1st Person: “Marry had a little lamb, little lamb…”
2ed Person heard 1st person and says: “Marry had a little lamb, little lamb…”
3rd Person will say: “Marry had a little lamb, little lamb…”

Each hop repeats the message. So you multiply the how long the radio takes to transmit a message by how many radios are allowed to repeat it.

To improve the range the project has settings that are equivalent to a person speaking slowly and enunciating and saying the same thing in slightly different ways to make sure the message is understood by the receiver.

Stay away from the car antennas unless you are going to remove the long cables attached to them. Those cables can absorb more of the signal than you would gain by having a ‘better’ antenna on the end. These devices have very low transmit power and any loss due to cables or poor antenna design will have a big impact on range.

Water absorbs radio energy most at 2.4 ghz. 915mhz is pretty far off from that. Vegetation will likely be the biggest issue.

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Thanks, that is helpful.

Are there best practices for adjusting the spread-factor? I’m still pretty unclear about what the implications of that are.

It was this site with a few articles about lora antennas and range that got me thinking about that car-roof style one.

It looks like the Moxon’s take a long time to ship from aliexpress. Does anyone here have a source of a Canadian or US supplier for that type of antenna?

And finally, what kind of connector is there on these TBeams? So I know what to look for when buying another external antenna. Or if an adapter is needed.

Thanks,

Just wanted to chime in here about a few things!

re: range of standard antennas, I’ve had no trouble getting 20+ miles (32 km) between heltec devices with the factory antenna. Granted I am in a low humidity area, but I’m transmitting directly over the city of Los Angeles. So I would say give it a try with the antennas that come with your radios before you go buying fancy and expensive ones.

re: running off large battery I run my repeater nodes off of 500 watt hour scooter batteries. (about 40 18650s) I get 5-6 weeks tops. So be conservative with your estimates of how long a usb battery pack might run. If you have a solar option go for it.

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SMA female, the “normal” type, not the so-called “reverse polarity” or “RP” type. Some T-Beam clones have a much smaller U.FL connector, I’d avoid these as they’re less robust.

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Not a T-Beam, but here’s a picture of the two connector types, side by side:

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We are discussing these topics on a public platform. What we talk about will likely be visible to a lot of people and agencies for a very long time. It amazes me how many people come here and say I’m in a remote area so I’ll never get caught but share all kinds of information about themselves, their location, and strong desire to break the law.

Sure, it’s likely not a big deal now. But what about later when the FCC AI Enforcement bot gets going? Or equivalent.

I would not be surprised if right now you happened to be in China your social credit score would be effected by such on-line talk. Who knows what the world and internet will look like ten years from now.

It’s really simple.

Fast transmit settings have short range.

Slow transmit settings have longer range.

Messages are sent quickly with fast settings. Can take much longer on the very slow settings.

Your choice sets an upper limit to the number of messages that can be sent in a given time period.

Just start thinking of people spread out in a huge conference hall where only one person can talk at a time and the rest are trying to hear what is being said.

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Good point, and I agree. I removed that comment. cheers.

Thanks everyone for all the details. It’s clarified a lot.

And good to know about the batteries. Our plan has revised to utilize solar and a large battery as I don’t want be hiking through to all the nodes every week or two.

Has anyone used the wifi ap function with the web interface to allow multiple people per node to send messages? Or is that even possible? I’m thinking for the single node that are in the camp itself.

I’d say the WIFI functionality is still very much in the alpha stages ( ie. issues with persistence of past messages if the web page is reloaded.)