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The bigger the better? Good idea to use a big Helium antenna with a tiny node? (lemmy.world)

submitted 3 weeks ago* (last edited 3 weeks ago) by [email protected] to c/[email protected]

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Just out of curiosity and inspired by a previous post here, i ordered two XIAO ESP32S3 - Wio-SX1262 Kits and a SenseCAP Card Tracker T1000-E.

I dont expect much if any nodes in the area around so the plan is to put one ESP+SX1262 up as a Router to the Internet (if this is the correct wording). The other one can be a sensor later on but first i want to test out the GPS tracking around the area (countryside).

As the SX1262 only comes with a small antenna, i thought about getting a used big (like 6dbi) Helium antenna for cheap to increase the range of the Router.

Whould this be an acceptable setup to start with, or just stupid? (especially the antenna and Router Part?)

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[–] [email protected] 2 points 3 weeks ago* (last edited 3 weeks ago) (1 children)

I've been using the Meshtastic site planner (https://site.meshtastic.org/) to plan out my mesh before committing to anything. Among other variables, you can plug in the antenna gains/heights to get a good idea of what your coverage will be (though it is just an estimate). A 6 dBi antenna and a few meters of height can go a long way from the results I've been seeing. The biggest factor is line of sight, so getting your gateway node up as high above the "smaller" nodes will give the best results regardless of which antenna you go with.

if this is the correct wording

I think "gateway" is the more correct term. From what I've read in the docs, "router" is usually used for nodes configured with the "router" role (which is different from a node connected to the internet via MQTT). In most cases, it's recommended to just keep all the nodes in "client" role since the "router" role behavior can be counter-productive in many cases.

[–] [email protected] 2 points 3 weeks ago (1 children)

I would be careful about using high gain antennas over 3dbi because while the signal can transmit physically farther, it also is a narrower window of signal and can be blocked by elevation changes. As an example, somebody with a 3DBI antenna would be able to talk to somebody on an airplane, but somebody with a 10DBI antenna would not.

[–] [email protected] 1 points 3 weeks ago

I'll second this. My 6 dBi antenna was able to hit a plane, but only because it was also 50 miles away. The cone on a 10 dBi would be too narrow even for that.

[–] [email protected] 2 points 3 weeks ago

Don't do this. Do a maximum of three DBI. The reason is higher DBI gain antennas cause your antenna to be very narrow, and so steep elevation changes or nodes that are trying to access your device from a different elevation can be easily blocked. A 3DBI antenna has 2x gain over a 0DBI antenna and yet still retains its spherical radiation pattern.

[–] [email protected] 1 points 3 weeks ago (1 children)

From first principles, there’s very little gain from antenna size beyond 1/4 of the wavelength. Something to keep in mind.

[–] [email protected] 2 points 3 weeks ago (1 children)

As someone who is completely new to this, would you mind expanding on your comment?

[–] [email protected] 3 points 3 weeks ago* (last edited 3 weeks ago) (1 children)

Gee, it’s been over 20 years since I studied this. Let me see if I can explain this quickly workout making too much a fool of myself. Let’s talk Amplitude Modulation because it’s the simplest. You take the signal you want to transmit and multiply by a carrier wave, a sinusoid of constant frequency. I hope you remember from high school physics that the higher the frequency, the shorter the wavelength.

Basically, your antenna has to excite the electromagnetic field around it in the frequency of its signal. One way you can do that is by using an antenna with the same size as the wavelength. So you charge and discharge the antenna according to your signal and you’re sure the whole wave will “fit” inside your exciting medium. Electromagnetic wavelengths are usually pretty big though (in the AM range we’re talking hundreds of meters). So let’s save some money by halving the antenna and transmitting half of the wave at a time. There’s some transmission loss, but it’s not bad. Halve it again, and again… you get the idea. You’ll have to have fast circuits to switch the signal between its several levels within each cycle of the carrier frequency, but it’s doable.

Now, because of how physics works in a way I didn’t quite learn in the first place, the transmission loss is quite minimal at big fractions of the wavelength but accelerates as you keep halving the antenna. So most AM antennas for longer range transition were like 1/32-1/8 of the wavelength in size - still very big, and used nowadays to attach cellular antennas to. I think the biggest one was a half wavelength antenna in Russia that consumed hundreds of watts and could basically transmit to anywhere in the world.

AM is in the kilohertz range. IIRC LoRa is in the free gigahertz range, so their full size antennas would be a million times smaller than AM. And since you don’t get much better transmissions from something larger than 1/4 length…

Of course, that’s without taking into account advances in technology. Which is why you get positive dB antennas out there (the ones we just talked about all had negative gain). Antennas are a mind boggling hard subject to get into. EMI in general is. Like my professor used to say: You are an antenna! Everything is.

Well, what I wrote doesn’t help much, does it? I hope I at least didn’t make things more confusing. It sure was hard for me in college with a good professor. It’s not going to be easy with me over a forum post. I did my best.

[–] [email protected] 2 points 3 weeks ago (1 children)

Thank you for the detail and I apologize if I gave you school flashback PTSD! Lots to pore over.

[–] [email protected] 2 points 3 weeks ago* (last edited 3 weeks ago)

Nothing to apologize for. It’s just one of those things I didn’t end up using professionally so it just accumulated brain dust.