Brian Roebuck
Site Admin
Caver
Caving - the one activity that really brings you to your knees!
Posts: 2,732
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Post by Brian Roebuck on Jan 25, 2007 18:28:37 GMT -5
NZ, I like the photos and obviously have an interest in radios and caves. I never delved into cave radio though. What band on the HF transceiver were they using BTW? I am sure the extra power output gets the signal out better than handhled units although antenna design and construction can make up for a lot. What is more important in cave radio - power out or antenna? Any other technical details would be appreciated. This is a cool thread!
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Timebot
Newby
Once a caver, always a caver.
Posts: 8
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Post by Timebot on Jan 25, 2007 20:49:39 GMT -5
I have my amateur license (have had it since 1982 or so) and find the subject interesting. I would think it would be difficult to transmit from underground unless wired in to an antenna on the surface. I'm curious about experimenting but don't have access to anything but 2-meter at the moment. (And that won't do!) Julie (N0vde)
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NZcaver
Beginner
U.S. Caver
Posts: 140
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Post by NZcaver on Jan 25, 2007 21:12:13 GMT -5
Hey NZ, it seems you must be really involved with field phones and cave radios. Care to tell us more? I dabble in this a little, that's all. Others I've worked with (and some I haven't) deserve much of the credit in the ongoing development of cave radio. I just like the idea of trying to effectively bridge the gap between caving and communications - especially in the context of cave rescue. Also it helps to know a wee bit about the subject when one ends up teaching it occasionally... therefore I am grateful for any input from others.
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NZcaver
Beginner
U.S. Caver
Posts: 140
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Post by NZcaver on Jan 25, 2007 21:39:21 GMT -5
NZ, I like the photos and obviously have an interest in radios and caves. I never delved into cave radio though. What band on the HF transceiver were they using BTW? I am sure the extra power output gets the signal out better than handhled units although antenna design and construction can make up for a lot. What is more important in cave radio - power out or antenna? Any other technical details would be appreciated. This is a cool thread! Output power and antenna efficiency are both important factors, as are the frequency, mode, and grounding. More power usually helps, but is seldom the crucial factor in communicating underground. Because traditional antennas always emit signals relative to ground, wireless communication underground becomes fundamentally a whole different ballgame in most caves. It's fun to confuse regular hams with this innocent question... "but what if your antenna is located 1000 feet BELOW the ground?" As well as the loop and whip antennas in the photos, compact ferrite core antennas are also used successfully with cave radios. Unfortunately I can't give you the specifics of the particular testing you asked about, but I can tell you it was in the lower half of the HF bands. None of the material I've produced on the subject of cave radio can really be considered "technical" - but thankfully a number of others have some good stuff out there on the internet. CB transverter for cave radio - radiolocation.tripod.com/Transverter/Transverter.html (beware of pop-ups) French System Nicola - naylorgr.perso.cegetel.net/cave_radio/SYTEME_NICOLA_Mk2.html
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NZcaver
Beginner
U.S. Caver
Posts: 140
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Post by NZcaver on Jan 25, 2007 21:58:37 GMT -5
I have my amateur license (have had it since 1982 or so) and find the subject interesting. I would think it would be difficult to transmit from underground unless wired in to an antenna on the surface. I'm curious about experimenting but don't have access to anything but 2-meter at the moment. (And that won't do!) Julie (N0vde) Ah, but trailing a coax from your underground transmitter all the way back to the surface rather defeats the purpose of using wireless communication. You might as well just run the standard field telephone system underground, and link it to a regular VHF or UHF radio at the surface via a phone patch. This is not that hard to do, and has been used during numerous mock cave rescues, and some real ones. Funny you should mention the 2m band. While testing HF cave radio in a semi-dry cave in Arizona (a hundred feet down, and a long way from the entrance), I had forgotten that my dualband handheld was still on. Imagine my surprise when I heard a voice from the surface on 2m. And, even more surprising, they could hear my reply! It's weird - in the same place in the cave, we heard a guy in Texas tuning up on HF. I'm sure this is a very rare example of "radio-transparent" karst, but it does exist...
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Brian Roebuck
Site Admin
Caver
Caving - the one activity that really brings you to your knees!
Posts: 2,732
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Post by Brian Roebuck on Jan 25, 2007 21:59:56 GMT -5
I checked out both links NZ and they are great! I have no problems with pop-ups on my Mac though! ;D
I hadn't thought about signals relative to ground and that is interesting to ponder. I suppose the low frequencies work great in solid rock but worse in areas where they have to pass through less dense layers. I'll have to read up on cave radios more to understand the antenna issues though. Thanks for clueing me in on some of the fine points of this facinating use of radios.
I wonder if wikipedia has anything on cave radio? Hmmm I checked and no they don't - so far.
As for radio transparent Karst - that is interesting. I work in a below grade area with a long concrete structure that houses a long steel tank. Using our older lower frequency radios worked pretty good even inside the steel tank provided doors were open. The newer higher frequency radios don't do well at all and we resorted to repeaters and big amps with yagi antennas to beam stuff up and down the room. There have been times however when communication magically worked without all the extra power and antennas. I imagine it was due to certain conditions in the soil, air, water, or whatever that made things work. It's kinda like tropospheric ducting when your signal bounce up and down along between layers of air and travel super long distances. Sometimes things just work. Interesting!
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L Roebuck
Technical Support
Caving
^V^ Just a caver
Posts: 2,023
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Post by L Roebuck on Jan 25, 2007 22:18:37 GMT -5
I dabble in this a little, that's all. Others I've worked with (and some I haven't) deserve much of the credit in the ongoing development of cave radio. Oh, why do I get the feeling you are just being a bit modest? You do a good job of bridging the gap between caving and communications!
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