They use following radio module: linx trm-315-lt, the max output power is only 10mW:
I’ve searched many hours for suitable low-requency radio modules but found nothing. I can think of so many applications or LoRa but as you say underwater might just not be one.
Can you think of suitable radio modules?
Thanks for the valuable input, I agree that there are better options than LoRa for underwater communication but I still think the transmission could be a few meters:
and strongly depends on the conductivity of the water.
That would require investing in a device and gateway that aren’t useful for the actual goal.
You could do it if you like, it makes absolutely no sense for the asker to waste their money doing so.
(Yes, one could run tests with two nodes and RadioHead… but the greater principle here is applying some common sense to recognizing grossly unsuitable ideas before sinking time and money into them)
From minute 14:00 on, gateway placed above water 1m @SF12: https://www.youtube.com/watch?reload=9&v=ZK-ttu5xrIE , minute 17:50 it is suggested to equip a fish with a LoRa tracker and just get the signal if it swims on the surface.
So to sum up, there are proof of concepts up to 3m. BUT: I am still unsure what RF communication is suitable then… :).
I know this is a LoRa-forum but eventually you can still recommend me sth.
I’ve recently opened a thread about small-sized LoRa modules for under water communication:
I haven’t completely dropped the idea of using VHF and UHF bands to bridge a couple of meters in water but I’d like to emphasize here again that VHF/UHF radio modules and under water communication is not a good match.
Anyways, on my search or lower frequency modules I came across this series from hoperf:
RFM98PW https://www.hoperf.com/modules/lora/RFM98P.html
The model number RFM98PW-169S2 supports 169MHz at 27dBm.
Has anyone of you experience with these modules and in particular what gateways can be used for those?
In theory, most gateway based on SX1302 should support it since it is usually paired with a SX1250 as RF front end which cover the band 150-960 MHz. But the antenna matching is typically targeted for 868/926MHz, so I have no idea what kind of performance you can get with off the shelf gateway …
VHF isn’t going to make enough of a difference to make this idea workable, and your costs in using atypical hardware will go through the roof.
Please stop chasing dead ends; if you need to get a signal out from under water, you’re in the regime of kilohertz to at most of few megahertz, or more likely not using RF at all. And in any case you’re talking to a very nearby pickup antenna.
If you have some other scheme for getting from the shellfish beds to a box on a pole on the shore, then you could possibly consider LoRa from there, though realistically given all the investment in gear for one small area you might as well just put a mobile data modem in it and not suffer the very extreme limitations on how much data you’d be able to send from a single LoRa device.
169MHz might sound “low-frequency” compared to regular LoRa or BLE or so, but when it comes to under-water RF communication it’ still quite high. Attenuation in water is something like 0.0173*SQRT(f) in dB/meter. This gives around 200dB/m attenuation - no point. Submarines use frequencies in the order of 10kHz for RF communication and the above is the reason why.
@cslorabox as you say, I’ll probably end ‘chasing dead ends’ and see for a solution to pull out the antenna from the water. Anyways, we’ll also do some testing together with a university and I hope to get back with some quantitative (while most likely not surprising) results.
@chip45 that’s a nice selection of products you have there!
There are similar looking allocations in the UK, although I dont read German.
That frequency could be used for point to point LoRa. But thats not the point I was making, remember this is the TTN forum.
When I checked the detail in IRE2030, it did not seem practical to set up a proper TTN node\gateway arrangement, not enough bandwidth available and duty cycle allowed is mostly 0.1% or 0.001%
How much bandwidth\dutycycle is available in Germany, assuming you do read German that is ?
I assume you are confusing that with 125Khz bandwidth - and that is to confuse LoRa wirh LoRaWAN. LoRaWAN ia an instantiation of a network standard, protocol, architecture etc. that builds off the LoRa RF physical layer implementation and they are not the same thing.
@ecosoph 169Mhz is commonly used IIRC in Smart Metering applications and similar low power, low data rate applications - esp in S.Europe. 169Mhz is a band available in many area of the world. It has an advantage over the higher UHF bands (863/868/905/915/926) etc in terms of range and also for into building (from external infrastructure) penetration and ability to penetrate into in ground metering boxes and water meter pits & e.g. water distribution infrastructure monitoring points.
For the reasons (of physics) above it is better than 868/915Mhz bands for small amount of water penetration…but not by much, as pointed out above.
LoRa devices - either running LoRa modulation or classic/legacy modes like FSK/(g)FSK are used in many applications in that band and at volume by such meter manufacturers. If you look at the device data sheets for many of the LoRa (node focussed) Si devices they include suppport for such frequency bands. As noted, however, at such lower frequencies the available bandwidth and channels are similarly & significantly reduced thereby further limiting the max data rates available to end applications. A fact that I believe was a consideration when the LoRa Alliance establisted LoRaWAN as a standard targeting (initially) the higher UHF bands. Also note the RF front end devices (SX125x) that support the LoRa ‘Gateway’ baseband processing silicon (SX13xx) also have versions with options for such low bands -)
LoRa & LoRaWAN have found multiple uses at the water/air boundary - where devices may submerge a few cm and/or get splashed, esp where they act as surface data comms devices for sensors tethered deeper down or closely attached below the water line (Swimming pool water temp - and even water quality monitoring devices, back-up water vests/jackets, water sport trackers, etc.), however, deeper water penetration applications (Meters+) are not an option unless devices ‘surface’ periodically to send any captured telemetry.
