In USA, the 3.9 MHz (75 meter band) and 7 MHz (40 meter band) SSB frequencies can be operated with a General Class, Advanced Class, or Amateur Extra Class license. When underground, you can use a common HF mobile SSB transceiver for these frequencies. Small HF portable transceivers such as Yaesu FT-817 are often utilized for cave communications underground, with portable antennas such as Super Antenna MP1DXTR80 or Super Antenna MP1DXMAX SuperWhips. Set up a temporary base station outside the entrance to the mine. Many of these setups can be operated /Pedestrian Mobile or /Mobile underground, and can easily talk to each other or talk to the entrance station. A simple VOX patch at the entrance station could join the HF and VHF/UHF system together so more units can talk. Here is a reprint of an article I wrote in Speleonics (Journal of the Electronics Section of the NSS) about communication and radiocation in caves.
Leaky feeder isn't even on the table...unless Land Ops has $350,000 it wants to burn Bonnie has the practical solutions.
Holy Guacamole! You said that right. It's not on the table, heck, it's not even in the same universe. You sure you got your numbers right? I know it's somewhat of a science, but where's all the cost going to? I like Bonnie better than you now, lol.
Yep...numbers are right...I was the project manager. Leaky feeder cable is stupid expensive and is custom made to the frequencies to be used. The cable we used is made in Germany, and is about 2 inches in diameter. It's heavy as a dead senator, difficult to bend without kinking, and a bear to hang. It requires duplexers, amplifiers, filters, power supplies, etc....and in our case one set of each at both ends of the tunnel (1/2 mile in diameter and 40 feet deep, with a bisecting cross tunnel). Plus we had to daylight the yagis out of the tunnel which was 3 runs of heavy coax out of the tunnels. The customer was delighted with the installation as now everyone had cell phone coverage and the fire department had P25 coverage. One cool feature of leaky coax is that we could get about 2/3 of the way around the 1/2 mile tunnel simplex with just the feeder cable hung and a 5 watt hand talkie...with no equipment turned on...whereas without it simplex distances were about 100 feet...or just past line of sight.
ok, So you have first hand experience. I understand more now. Quite an elaborate system and better suited for the commercial enterprise that is doing the mining I suppose. Excellent info. I appreciate the detailed explanation. For sure this will be a topic at the next Land Ops camp fire. I pictured it all different. I did not imagine the coax being so thick. Perhaps if you have some pictures of the install you might be able to post here I'd welcome that. 73s
Here we have about 6 guys hoisting it up to the ceiling of the synchrotron ring tunnel so we can get it up on the hangars without kinking it as it comes off the spool. It's about 40 feet underground here.
I see. It looks like any other conduit, but within the exterior casing is the coax with the jacket cuttings? I don't see the cut outs or "leaks" for RF. Are those within the aluminum colored enclosure? It looks pretty ridged to be coming off a spool. The color is deceiving as it looks aluminum. But then again duck tape is that color too, lol. So, if my assumption is correct, the RF leaks/slots are precut BEFORE you spool it up. Curious!
Solid copper shield with cut outs is under the black plastic protective jacket. The black plastic looks silver from camera angle and reflection. It does come off a spool, but the spool is quite large to keep the bend radius within spec. All shield cuts are done at the factory before the plastic jacket is applied.
Ahhh yes, I see it now. The flourescent lighting makes the black jacket look silver. Got it. And as I guessed the cut outs are contained under that jacket. If you could ever find a cut away view of the inside of this please post it. It looks to be a two inch pipe. Copper inside, that's why it is so expensive for the materials and I'm sure the labor is more than half the cost.
worked in drift coal mine in wales 2 miles in. antenna for handheld to speak to surface was 2 miles long from surface to undergr0und. hi . also we could contact surface by wired phone. now all mines shut down hi . gw0tau paul.
okay so this raises the question about what kind of mine this is. I'm pretty sure that tunnel size, wall thickness and the type of earth you're in all must be factored in. I had someone mention that some subways use the leaky feeder (very expensive) method but that they chose frequency based on tunnel size and shape. I'd be curious to know how radio waves then function in a coal mine shaft, vs solid rock vs soft earth. Question back at you...These handhelds worked without any other form of repeating??? I heard the subway leaky coax served as a repeater for handheld units. When you say the antenna was 2 miles long, are you referring to a leaky feeder type coax? I think that's what you saying. Thanks for the reply
hand helds just tx to antenna wire. to radio on surface wire abt 6 foot up on side of tunnel from surface to bottom of drift radios on vhf.colliery name betws anthracite coal mine in a town called ammanford in west wales . maybe a gud thing that maggie thatcher closed it many accidents 3 guys killed when i worked there mine closed abt 25 years ago .i think it was copper wire enclosed in pvc .
We tested the leaky feeder with all electrical components turned off...just the cable. With 5 watt VHF hand talkies we got about 2/3 of the way around the 0.5 mile long ring tunnel before we lost signal (about 1/3 of a mile). My guess is that 2 miles of VHF or UHF coms on a leaky feeder almost certainly had an amplifier somewhere along the way...either that or the cable was much more efficient by having fewer cuts for various bands or the hand talkies were much more powerful than 5 watts.
From what I've learned from you that sounds about right. I appreciate everything you've shared. So we're going to start focusing on low RF and what we need to do to test that the next time around in May.
