Cave radio

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Postby Teresa » Mar 9, 2006 11:24 pm

I don't know about the Ray Cole design, but the lower you go in hertz, the less information the signal can carry. This is why so-called voice cave radios are towards the higher frequencies- voice modulation requires more information carrying capacity than a simple on/off binary of Morse.

That being said: (and I come from a family of amateur operators, (Dad was ex-Signal Corps) who often entertained themselves tapping code on the kitchen table) you have a couple of other options. One: design your own code-- using Morse or some sort of beep code to reference phrases and sentences--and a codebook. Some radio people have tried hooking a computer keyboard to a Morse generator--you type J and get a .--- pulse through the radio--so you really don't need to know Morse and send with a telegraph key. If you can touch type, this is probably a doable option, especially now, since people are used to email.
There are also experiments going on with computerized signal compression and modulation which give the speaking voice a smaller footprint (like an mp3) without becoming incomprehensible. Smaller signal, lower in the frequency range (and farther through the rock) you can go.

Since no one else has mentioned it, how about the NSS Electronics Section? Their newsletter, Speleonics, has numerous schematics in it for conventional cave radios, and the folks who hang out there include lots of double EEs and licensed ham operators. An electronics degree, a ham license, an NSS membership and a soldering iron, and these folks (mostly fellows) are dangerous!
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Postby NZcaver » Mar 10, 2006 1:25 am

Teresa wrote:...but the lower you go in hertz, the less information the signal can carry. This is why so-called voice cave radios are towards the higher frequencies- voice modulation requires more information carrying capacity than a simple on/off binary of Morse.

Not necessarily - bandwidth and mode comes into play too. The cave radio sets I've used most recently work great between 45-185 kHz (SSB voice) - and that's pretty low! (Being careful not to interfere with LORAN etc, of course...) :wink:

That being said: (and I come from a family of amateur operators, (Dad was ex-Signal Corps) who often entertained themselves tapping code on the kitchen table)...

Snap! I come from a family of hams too, and I'm ex-Signal Corps to boot (amongst other things). Aah, tapping code on the kitchen table... :big grin:

There are also experiments going on with computerized signal compression and modulation which give the speaking voice a smaller footprint (like an mp3) without becoming incomprehensible. Smaller signal, lower in the frequency range (and farther through the rock) you can go.

Hmmm, not to mention sending data and photos/SSTV around caves too - all good fun stuff... :goodjob:

Since no one else has mentioned it, how about the NSS Electronics Section?

Oops! Completely forgot about that. http://www.caves.org/section/commelect/ :grin:
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Postby Teresa » Mar 10, 2006 8:43 am

NZcaver wrote:
Teresa wrote:...but the lower you go in hertz, the less information the signal can carry. This is why so-called voice cave radios are towards the higher frequencies- voice modulation requires more information carrying capacity than a simple on/off binary of Morse.

Not necessarily - bandwidth and mode comes into play too. The cave radio sets I've used most recently work great between 45-185 kHz (SSB voice) - and that's pretty low! (Being careful not to interfere with LORAN etc, of course...) :wink:

I know that. Just trying to simplify it for readers who don't have the lingo (like, I know about SSB voice, but then I grew up thinking transistors were something you stepped on in your brother's bedroom and *everyone* listened to international shortwave after dinner.) One of the radios I am aware of is below 10kHz-- at that freq you start running into the information problem.
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Postby NZcaver » Mar 10, 2006 4:33 pm

Teresa wrote:I know that.

Great!
One of the radios I am aware of is below 10kHz-- at that freq you start running into the information problem.

Can't say I've ever used anything below 10kHz, but I'd imagine you could run into all sorts of issues THAT low in frequency. Point taken... :neutral:
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Postby ian mckenzie » Mar 10, 2006 5:18 pm

The really low frequencies are not intended for voice, or Morse - they are used for location work by measuring the geometry of the underground signal on the surface. Those radios usually have a dual setting so you can use voice as well, tho the range is reduced when you do so.
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