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Subject: Re: You use different lenses underwater because the speed of light is different



Grumman-581 wrote:

> "David J. Littleboy" wrote in message
> news:e2n3ee$eob$1@nnrp.gol.com...
>
>>I had a friend at MIT doing submarine radio.
>>
>>Me: Huh? Radio waves don't propagate in water???
>>Him: Sure they do, but only at low frequencies, e.g. around 1 Hz.
>>Me: 1 Hz??? That's completely useless.
>>Him: Not at all. All you need to transmit is one bit: fire the nuke-tipped
>>missile or not.
>
>
> Not quite acurate... Navy subs use VLF 3-30 kHz and ELF 40-80 Hz... The get
> about 50 bps out of ELF, if I remember correctly... Enough to tell them to
> do previously designated tasks... Not enough for general communication,
> especially since it is one way... Enough to tell them to come to the surface
> so that they can use their higher frequency radios...
>

A few cavers I hang around with are also interested in underground radio
for surveys, beacons, emergency communications, and whatnot. We tested a
setup at a carrier frequency of 873 Hz and found that it made a
stellar directional survey beacon, capable of sending signals through
hundreds of feet of limestone. Also good for predetermined slow
data-rate messages such as we're fine, we need help, is it raining?

We set one transmitting/receiving loop flat on the floor of the cave.
Then we came back up and started kinda dowsing with the other. When we
tipped the loop perpendicular to the spot directly over the transmitter,
the signal nulled out sharply. W000TPTH! Try modulating 873Hz w/voice
and you run into problems. DOH!

Europe has a small 136-ish kHz ham radio band to play with. At that
frequency, rock attenuates radio waves quite a bit more.

Corry
--
It Came From C. L. Smith's Unclaimed Mysteries.
http://www.unclaimedmysteries.net


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You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>Re: You use different lenses underwater because the speed of light is different =>

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