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Two nodes with different antenna gains? (lemmy.ca)

submitted 1 week ago* (last edited 1 week ago) by avidamoeba@lemmy.ca to c/meshtastic@mander.xyz

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Has anyone tried a similar abomination? The main node I use has a 2dBi antenna. A 5dBi antenna performs worse for connecting to most of the nodes in my vicinity. It does however connect to some nodes further away. So I decided to try adding a separate 5dBi node. That way devices close by could choose to route via either node, whichever seems better. Or traffic could jump between the two taking local traffic from the 2dBi node and beaming it further via the 5dBi node at the expense of an extra hop. Thoughts, experiences?

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[–] Sendpicsofsandwiches@sh.itjust.works 9 points 1 week ago* (last edited 1 week ago) (1 children)

I think this sounds like a really good idea, the only thing I could think of to change might be to separate the two nodes a bit more. I don't know if this is as much of a problem on 915mhz since the wavelength is so short but generally you would want to keep two antennas farther apart to prevent interference, from having metal near by or from potential cross-talk

[–] avidamoeba@lemmy.ca 4 points 1 week ago (2 children)

I'm thinking about mounting two radios in a single box with one antenna sticking out of the top and one from the bottom. Like a light sabre.

[–] shortwavesurfer@lemmy.zip 4 points 1 week ago (1 children)

Rule of thumb is to keep the antennas at least one wavelength apart. On the 915 MHz band, that's 33 centimeters. So that should be the distance between the two antennas at minimum.

[–] avidamoeba@lemmy.ca 1 points 1 week ago (1 children)

Would that matter if only one is transmitting at a time?

[–] shortwavesurfer@lemmy.zip 2 points 1 week ago

possibly as it could still couple to the other antenna and throw off the standing wave ratio

[–] Sendpicsofsandwiches@sh.itjust.works 3 points 1 week ago (1 children)

Yeah, I think that would definitely do the trick! I'm thinking about doing a similar setup to make a big meshtastic repeater node for my house that I can use with smaller handheld nodes so that I can get connected to the farther away networks in the city

[–] shortwavesurfer@lemmy.zip 4 points 1 week ago (1 children)

CLIENT_BASE, not repeater or router

[–] avidamoeba@lemmy.ca 3 points 1 week ago* (last edited 1 week ago)

I concur, do not use REPEATER/ROUTER roles unless you know what you're doing (have a very high mast, hill, high building roof, etc. read the doc) as it's very likely you'd be harming the network instead of helping. Using a device configured as CLIENT/CLIENT_BASE extends the network without risking harm.

[–] sobchak@programming.dev 5 points 1 week ago (1 children)

I don't know much about radios, so I may be wrong, but I think I've heard that having a transmitter close to a receiver can "desensitize" the receiver. Since both are TX/RX, I think this could cause problems. With Lora being digital and intermittent, IDK though.

[–] remotelove@lemmy.ca 1 points 1 week ago

Harmonic frequencies are more likely to be an issue.

If you have an antenna transmitting at 2.4ghz, you will also see subharmonic bumps at 1.2ghz, 800mhz, etc. A receiver at 800mhz could potentially get "washed out", or overpowered, by a 2.4ghz transmitter that is too close simply because of subharmonics.

Transmitters aren't perfect either. While you can get really strong transmissions at very specific frequencies that can propagate really far, electronics resonate at many frequencies and that resonance will make it to a TX antenna as noise.

Unless the antennas are designed to work together, you shouldn't put them that close together. (I am also speculating that in extreme cases, a weird configuration like that could detune the transmitter antenna in a such a way that it would blow out the transmission circuit. I dunno about that though.)

[–] fubarx@lemmy.world 4 points 1 week ago

There's a ton of knowledge on antenna placement in the ARRL world: https://www.arrl.org/arrl-antenna-book

May want to connect with folks in those communities.