I How do submarines communicate with radio waves?

[cmb]

It is expected that ELF signals are secret. A proper OTP system makes it unbreakable if the key chain is secure.
https://en.wikipedia.org/wiki/One-time_pad
Advances in technology have made key distribution problems easier to solve.

That wasn't what I really meant.

I mean, if I was setting up the communication chain, I would make it so that it just wouldn't really matter what the three letter transmission is.

It could just mean 'Moscow calling' and they could publish it on the internet.

But if the MO on the captain's mission delegation sheet says 'shallow surface if you get a 'Moscow Calling' signal at 3PM, Moscow time, because there might be a message waiting for you', then that is all that is needed.

If I was OOW/OC and an ELF signal was detected (from either 'side'!), I might want to just pop up for an update anyway, if I felt it was safe.

I'm unclear what the fuss would be about trying to get messages encoded on ELF. If you make encryption part of the protocol it's just one more thing that can go wrong and create uncertainty. The crew will always be the ones that have to assess whether it is safe to come up, anyway, whatever signal they have received.

But, anyway, I have said that now, no need I repeat, so go ahead and pick up some ELF for yourself! It's not difficult actually, just string a big loop around the garden and wire it up to your computer's sound card and run a FFT app.

You get to see various anomalies and blips in all the LF bands, Schumann resonances and lightning whistlers and 'things'. :)

 

[Drakkith]

I'm unclear what the fuss would be about trying to get messages encoded on ELF. If you make encryption part of the protocol it's just one more thing that can go wrong and create uncertainty. The crew will always be the ones that have to assess whether it is safe to come up, anyway, whatever signal they have received.

It adds redundancy and flexibility to your submarine operations.

 

[artis]

@nsaspook one can see the 50hz powerline frequency being the most powerful one in that graph.
But then again powerlines with their overall length and location I guess make up the worlds largest low frequency antenna array ever built. Also the most powerful one.

I wonder why they don't use powerline wires to transmit the VLF isn't there a way to combine them or would the two frequencies cause some destructive interference?

 

[DaveE]

I wonder why they don't use powerline wires to transmit the VLF

Because the power companies and their customers would have a fit. I, for one, prefer my AC power in the plain version, not modulated with VLF.

 

[cmb]

@nsaspook one can see the 50hz powerline frequency being the most powerful one
...I wonder why they don't use powerline wires to transmit the VLF isn't there a way to combine them or would the two frequencies cause some destructive interference?

They could not modulate 50Hz (or 60Hz) because so much industrial kit runs off a reliance on that frequency.

Imagine if all the induction motors around the world had to speed up and slow down, just to sent a sub signal? hmmmm ... not going to happen.

The mains frequencies are tightly controlled, under legal compulsions, for precisely that reason.

 

[DaveE]

There's also a tremendous amount of noise at 50/60Hz and the harmonics. People that work with signal processing in this region know to avoid those frequencies for better S/N ratio.

 

[artis]

I wasn't saying one should directly use the very phase wire , just an additional wire but true , interference would be a problem I think more so for the VLF signal than the 50hz AC as that is much more powerful