Radio communication experiment

G6SWJ Opening post 6 years ago

I'll park this here for anybody that is interested and report back at some point in the future my findings.

I started an experiment a while back to see which was the more reliable communication method especially with model submarines.

The kit - 459 MHz packet radio / 459 Mhz LoRa / 459 Mhz openLRS / 868 Mhz packet radio - I have a homebrew 40 Mhz digital radio but it seems to have a mind of it's own so I have excluded it from this exercise.

I have several ideas on the antenna options. I have been playing with bits of string and wire for antennas for 40 years...

I will get the kit fired up and then once I have them all communicating I can start to play. The good news with these radio's is they all have an RSSI (Received Signal Strength Indicator) as part of the firmware which you can either read and store locally for analysis or send back as telemetry so there is an easy way to "scientifically" benchmark performance

I'll publish my findings assuming I don't loose it at the bottom of the lake...

Jonathan

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2 comments

RNinMunich Bronze
Fleet Admiral6 years ago
"have no idea where you get the frequencies you list. Are they available or are you generating them."
Hi Pete,
Haven't checked yet but I assume that those are open license packet radio frequencies.
I too am looking forward to to the results with great interest.
Especially with regard to 'submarine communications'!
I have experience of both real life and model sub COMMS and I know that real subs either have to surface or send up a Communications Buoy to get the antenna above the wet stuff to get a link in the HF/VHF/UHF bands and above. Underwater they use frequencies in the VLF (Very Low Frequency) band, a few KHz - nowhere near MHz, learned from the whales!, and a very slow data rate of a few bits per second, i.e. one letter or number/sec🤔 The TX antennas on land are measured in kilometres!
With models anything above 40MHz gets increasingly absorbed by the water as the frequency goes up. At 2.4Gigs you're only warming the pond water, just like your microwave oven warms your food by agitating the water molecules in your nosh.

Packet Radio just means that you are sending bursts of information in the form of short data telegrams, the Packets.
What's important here is the carrier frequency used; i.e. the "459 MHz packet radio / 459 Mhz LoRa / 459 Mhz openLRS / 868 Mhz" that Graham mentions.
I would not want to go below periscope depth, keeping the antenna above water, using those frequencies.
I would also build a Fail Safe circuit into the sub, hence Graham's other project.👍
That means on loss of the TX signal surfacing will be automatically activated.
Otherwise, he may well 'loose it at the bottom of the lake' 😭
The RSSI function will not help in that case. It's what is known as a 'Whoops, Sorry🤔' indicator in such applications. I.e. it'll work as long as his Packet Radio link feedback is established. From underwater!?
The frequencies Graham mentions are presumably generated on the little PCBs he has shown.
Don't get me wrong; I wish Graham every success in his endeavours🤞 but I have to admit that I'm sceptical when it comes to underwater comms at those frequencies!
Cheers, Doug 😎
Apropos COMMS buoys: I remember in the 90s discussing some ambitious COMMS refit projects for Type 206 subs with navies in various countries. Their ideas for several simultaneous HF, VHF and UHF COMM lines would have caused an interference chaos if all antennas were squashed into the conning tower, and would not have worked when submerged. After explaining why I jokingly suggested that they tow a raft with the additional antennas needed.
Lo and behold a year later a German company (related to the one that built the 206 subs🙄) started marketing COMMS Buoys that are used now by all sub operators today!😠
I should have patented the idea!!!! Grrrrr!
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MouldBuilder
Admiral6 years ago
I look forward to the results but have no idea where you get the frequencies you list. Are they available or are you generating them.
Peter.
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Radio communication experiment

Radio communication experiment