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Author Topic: Transmitting Out of a Deep Mine (mobile)  (Read 4581 times)
KI6QBM
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« on: March 04, 2017, 09:40:15 PM »

DRIVING INTO REWARD MINE
and Transmitting from deep inside the mine
VIDEO TRAIL REPORT https://youtu.be/isWYOsPJnJk

MOBILE RADIO TEST RAISES THE QUESTION

How do you communicate when you are deep inside the earth without running a telegraph line? Late last year the Land Ops Adventure Radio Club took several teams into the depths of the abandoned Reward Mine in California. Despite safety precautions this was still a fairly dangerous activity due to carbon monoxide levels and always the possibility of collapse. Even a few rocks coming off the ceiling could result in tragedy. Nevertheless, two teams drove their 4x4 mobile ham vehicles to the furthest extent and gave it a shot. This first trip was more for the thrill and adventure, but we did test our 2 meter radios and even with a relay with no success.

CAVE RADIO

2 Meter was an obvious failure. Since this trip many have shared with us either information about Cave Radios using very low RF to penetrate solid rock and a system called "leaky feeder" which is super costly. We share this adventure on ehamnet because we will be going back several times to Reward Mine with a greater emphasis on the radio test to the outside world.

SHARE
Please share info about underground transmittion stories that we might learn the best and most practical communication (via radio wave) to get a signal out of the mine. At furthest point (driving, then walking) we are almost .4 mile into the mine

VIDEO of the MINE ADVENTURE https://youtu.be/isWYOsPJnJk
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G8YMW
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« Reply #1 on: March 05, 2017, 08:07:36 AM »

There was an article in Radcom a few years ago.
Cannot remember the ins and outs too clearly but I think it was a long tunnel.
They found that the best band (of those they had) was 23cms with 70 cms worse and 2 metres the worst of the three.
But if you was penetration as opposed to reflections then I think you have to go right down in frequency
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73 de Tony
Windows 10:  Making me profane since March 2017
WV4L
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« Reply #2 on: March 05, 2017, 12:02:52 PM »

Our radio club was given a presentation by a spelunking(sp?) rescue group. Their go to for communications was wired communications systems back to the surface. They had tested emcomm radios to no avail. Even when they were able to place an individual directly above a rig below the surface at varying depths their was little confidence in that mode of communication.
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W8JX
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« Reply #3 on: March 05, 2017, 03:02:31 PM »

The US Navy and Russia has long used ELF (extremely low frequencies of 3 to 30 hz) for sending messages to and from submarines deployed around the world. I suspect it would work fine in a mine but antenna would be a challenge.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KI6QBM
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Posts: 8




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« Reply #4 on: March 05, 2017, 10:21:39 PM »

There was an article in Radcom a few years ago.
Cannot remember the ins and outs too clearly but I think it was a long tunnel.
They found that the best band (of those they had) was 23cms with 70 cms worse and 2 metres the worst of the three.
But if you was penetration as opposed to reflections then I think you have to go right down in frequency

We found that out. 2 meter didn't make it nearly anywhere in this tunnel past line of sight.
I heard from Kq6Xa she said in another forum  ..."In caves, she found that 2 watts at 7 MHz or 3.9 MHz SSB, with small whip antennas, will go through about a quarter mile to a half-mile of solid rock. Further if one station uses a longer antenna."
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KI6QBM
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« Reply #5 on: March 05, 2017, 10:24:52 PM »

The US Navy and Russia has long used ELF (extremely low frequencies of 3 to 30 hz) for sending messages to and from submarines deployed around the world. I suspect it would work fine in a mine but antenna would be a challenge.
Yes, I heard very low RF is better. ome of the radios we've seen for such things are homebrew. We're seeking the right frequencies and antennas to take out there again.
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KI6QBM
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« Reply #6 on: March 05, 2017, 10:27:36 PM »

Our radio club was given a presentation by a spelunking(sp?) rescue group. Their go to for communications was wired communications systems back to the surface. They had tested emcomm radios to no avail. Even when they were able to place an individual directly above a rig below the surface at varying depths their was little confidence in that mode of communication.
Thanks for sharing. I guess wire comms would be the way to go in a mine but might fail during cave ins. We're goping to stico with RF and see what we can accomplish.
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W8JX
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« Reply #7 on: March 06, 2017, 04:29:33 AM »


They found that the best band (of those they had) was 23cms with 70 cms worse and 2 meters the worst of the three.


I am not surprised that higher UHF frequencies work better within cave/tunnel system. 800 mhz or 1296/23cm should work pretty good within tunnels. Nature of wall fo tunnels would play a roll to with hard rock reflecting UHF signal down tunnel better than soft earth.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KG4RUL
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« Reply #8 on: March 06, 2017, 09:08:30 AM »

Radios work in subway tunnels.  Ever wonder how?  They run lengths of very leaky coaxial cable in the tunnels and hook them up to outside antennas.  Sort of a 'passive repeater'.  However, that is probably not feasible for mines.
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KI6QBM
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« Reply #9 on: March 06, 2017, 11:34:05 AM »

Radios work in subway tunnels.  Ever wonder how?  They run lengths of very leaky coaxial cable in the tunnels and hook them up to outside antennas.  Sort of a 'passive repeater'.  However, that is probably not feasible for mines.

Actually I heard about this elsewhere, I never thought about how subways, but I guess that makes sense. The person who installed them said they were super expensive. His project was like $350,000 for the "leaky feeder" coax. I saw a picture of the install, quite the undertaking. It's Coax with cut outs at intervals to let RF leak out.
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W8JX
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« Reply #10 on: March 06, 2017, 12:29:38 PM »

Apparently it seem in commercial mines the use HT frequencies of 200mhz to 4 ghz for in tunnel comm. Frequency used it seems depends on rock/soil type and shaft diameter. Main long range frequency and one generally used for search and rescue is abt 457 khz.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KI6QBM
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Posts: 8




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« Reply #11 on: March 06, 2017, 06:11:29 PM »

Apparently it seem in commercial mines the use HT frequencies of 200mhz to 4 ghz for in tunnel comm. Frequency used it seems depends on rock/soil type and shaft diameter. Main long range frequency and one generally used for search and rescue is abt 457 khz.

okay, that make sense. Tunnel diameter should have something to do with wave passage or reflectivity (bounce) and the optimum frequency (wave length) to be used. Then again some of the very low RF penetrates solid rock. Tunnels passing through soft earth verses solid rock should also be factored in. Thanks for sharing, it did not occur to me that the diameter of the tunnel and/or changing shape of the "tube" and wall material and thickness must be factored in. In this case it's pretty much solid rock.
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W8JX
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« Reply #12 on: March 06, 2017, 06:44:36 PM »

it did not occur to me that the diameter of the tunnel and/or changing shape of the "tube" and wall material and thickness must be factored in. In this case it's pretty much solid rock.

23 cm or better would likely work best here for tunnel comm. Also consider that unless you use a full sized 1/4 wave on a 2m HT you have a negative gain antenna on both ends when using them in a cave/tunnel. At higher frequencies it is possible to have more efficient antennas too.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KD0REQ
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« Reply #13 on: March 07, 2017, 09:18:23 AM »

repeaters.  the wifi model looks good to me for this.
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WB6BYU
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« Reply #14 on: March 15, 2017, 07:13:49 AM »

I think a WiFi "mesh network" with multiple repeaters would be the most likely to work well
over a variety of conditions.  (UHF / microwave reflections may be more reliable in a mine
with straight walls than in a natural cave.)

Most of the cave communications systems I've seen use LF / VLF with multi-turn loop
antennas.  These might be a meter square for portability, or somewhat larger with
folding arms when the cave is expected to have larger rooms where it can be set up.

I've seen a number of articles on such systems over the years - an internet search
for "cave communication" should bring up plenty of information.
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