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Post by colly0410 on Jun 13, 2015 14:19:54 GMT -5
I've been reading up on leaky feeder & tunnel transmitters two way radio systems using VHF & UHF radio, & through the earth mine communications (cave radio) using low frequency (long wave) radio. Were any of these systems used in coal mines?
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Post by John on Jun 13, 2015 14:46:18 GMT -5
I've been reading up on leaky feeder & tunnel transmitters two way radio systems using VHF & UHF radio, & through the earth mine communications (cave radio) using low frequency (long wave) radio. Were any of these systems used in coal mines?
A later version was installed at Angus Place Colliery when I was working there, repeaters were installed at conveyor switchgear, I believe it only had a 1.2Km range. Guy wires were run down one of the intake headings.
Again this was a VHF system, I never saw it working, I'll ask Kerry Morris what transpired with it, he was the Elec Engineer there, he's on holiday at the moment, so it will have to wait until he returns to Australia.
Propagation of radio signals as you're aware, has some strange things happen to them. During my early ham radio days, I chatted to a fellow ham in Reno Nevada from Sacramento...on a 5watt handy talky (HT) Impossible normally, on the 2 metre ham band, (144Mhz) on FM mode. There was a thunderstorm raging over the Sierras at the time, so my signal was being channeled under the storm clouds...The only explanation..
In enclosed environments like mine roads signals get absorbed very quickly, steel rings add another problem, and distance.
I understand VLF will penetrate the earth for quiet a distance, not sure how far, and has been used in mines rescue. Again, power and depth, no idea. My knowledge of propagation of signals is mostly in air and bouncing signals off of the upper atmosphere on HF bands. I have received my own signal on a long path return from Europe when I was in contact with a UK ham, odd hearing oneself on the back of an antenna, echos! |
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Post by tygwyn on Jun 13, 2015 17:09:20 GMT -5
Technology bois bach,their talking about supplying i-pads to electricians underground in Queensland,lol.
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clem
Trainee
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Post by clem on Jun 14, 2015 1:33:14 GMT -5
We used a system called a PED in Australia they ran an aerial on the surface over the workings and we had a receiver on our battery pack where we could receive a brief message say 8 words
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Post by John on Jun 14, 2015 6:45:08 GMT -5
We used a system called a PED in Australia they ran an aerial on the surface over the workings and we had a receiver on our battery pack where we could receive a brief message say 8 words
During WW2 experiments were carried out with buried antennas, mostly so as the enemy couldn't spot them from spotter planes, and it was found out most the the HF radio spectrum could be used for varying ranges of communications. HF = from the commercial broadcast band up to 30Mhz.
A lot of work was also carried out to find a suitable frequency for submarines while submerged, VLF was about the only part of the spectrum that could be used, and even then had to have an antenna with a float to hold the top above the seas surface. Salt water makes a great ground plane!
It was also found, post WW2, VLF could penetrate the earth, we are talking the low Khz frequencies, but that is too influenced by different strata like iron or other metal ores. |
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Post by John on Jun 14, 2015 6:46:08 GMT -5
We used a system called a PED in Australia they ran an aerial on the surface over the workings and we had a receiver on our battery pack where we could receive a brief message say 8 words |
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Post by John on Jun 14, 2015 9:15:51 GMT -5
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clem
Trainee
Posts: 3
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Post by clem on Jun 15, 2015 1:43:06 GMT -5
We used a system called a PED in Australia they ran an aerial on the surface over the workings and we had a receiver on our battery pack where we could receive a brief message say 8 words Might have been the system is used in most coal mines here the only difference is the cable is placed underground due to access restrictions on the surface Here is a link mstglobal.com/solutions/emergency-messaging/underground-coal-mining/ I hope it works. Also have a look at the people tracking systems they have... has caught a few people out even undermanagers |
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Post by John on Jun 15, 2015 10:20:53 GMT -5
Wasn't that tried out at Mt Isa??? Might have been the system is used in most coal mines here the only difference is the cable is placed underground due to access restrictions on the surface Here is a link mstglobal.com/solutions/emergency-messaging/underground-coal-mining/ I hope it works. Also have a look at the people tracking systems they have... has caught a few people out even undermanagers |
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Post by Wheldale on Jun 15, 2015 15:56:09 GMT -5
When I worked in South Africa there was a system called Ecam. It was used to communicate between the cage and engine driver, Usually for shaft inspections but one shaft I worked on it was solely used by the onsetters who travelled in the cage with the men.
The system had an "horse shoe" in the head gear that fitted around the winding rope, the cage had a telephone and shaft signalling key plus battery. Basically the communication signal was transmitted over the winding rope and picked up by the horse shoe in the headgear. This was an effective 2 way system.
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Post by Wheldale on Jun 15, 2015 16:03:57 GMT -5
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Post by John on Jun 15, 2015 16:51:33 GMT -5
Oddly enough, when I was at Boulby, they used the "low band" VHF band for two way communications with the shaft and engineman, "low Band" is the band below the 2 metre ham band, high band is the one above the 2metre ham band.
Boulby utilized FM handi talkies and a transceiver in the engine cabins, antenna was a multi element Yagi mounted in the towers and pointing down the shaft.
Communications were pretty good right down the shafts to below pit bottom.
There was one problem though, shaftsmen were apt to use "pit language" which caused the Post Office Telecommunications, (now known as Offcom) to send a written warning to CPL, with the possibility of a large fine should it continue.
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Post by colly0410 on Jun 15, 2015 17:31:24 GMT -5
I drove through the Dartford tunnel last year & listened to Absolute radio on 1215khz, I understand they use a leaky feeder to relay the Brookmans park transmitter also on 1215khz. I thought I'd experience some selective fading when both TX's came in at equal strength, but I didn't notice anything, the frequency control & phasing must have been spot on.... When I tune in Absolute radio on 1215khz here it's terrible with selective fading as we get Droitwich & Moorside Edge both coming in about equal on 1215khz as they use a sychronised network. They opened a relay at Trowel Moor on 1197khz at 5OO watts, that comes in perfect.... I wonder if they have problems with selective fading when they use multiple TX's on the same frequency underground? Unless they're too far apart to interfere with each other..
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Post by John on Jun 16, 2015 6:37:55 GMT -5
I drove through the Dartford tunnel last year & listened to Absolute radio on 1215khz, I understand they use a leaky feeder to relay the Brookmans park transmitter also on 1215khz. I thought I'd experience some selective fading when both TX's came in at equal strength, but I didn't notice anything, the frequency control & phasing must have been spot on.... When I tune in Absolute radio on 1215khz here it's terrible with selective fading as we get Droitwich & Moorside Edge both coming in about equal on 1215khz as they use a sychronised network. They opened a relay at Trowel Moor on 1197khz at 5OO watts, that comes in perfect.... I wonder if they have problems with selective fading when they use multiple TX's on the same frequency underground? Unless they're too far apart to interfere with each other..
But saying that, signal carriers can and do mix causing odd things to happen in receivers.
I like FM for phone, it's nice and clear, until a signal starts to get weak, then it starts to deteriorate big time, probably frequency shift??
SSB is the most efficient, but I have no idea how it would work in a mining environment. FM mode seems to be the most popular for voice communications.
I have received information on the Mine Radio installed at Angus Place, it was set up and was successful. |
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Post by colly0410 on Jun 16, 2015 12:12:09 GMT -5
I like FM for phone, it's nice and clear, until a signal starts to get weak, then it starts to deteriorate big time, probably frequency shift?? SSB is the most efficient, but I have no idea how it would work in a mining environment. FM mode seems to be the most popular for voice communications. I have received information on the Mine Radio installed at Angus Place, it was set up and was successful. [/b] [/quote] Of course FM has the 'capture effect' I'd forgotten about that, that would help a lot when two or more stations are being received at the same time.... I wonder if they use some sort of digital modulation with lots of FEC? (Forward Error Correction) Or would that get corrupted too much by the reflections underground? Just a thought I've had.. |
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Post by John on Jun 16, 2015 13:18:33 GMT -5
I've no idea Steve, the only actual radio experience I had U/G was around the mid 60's, I knew very little about radio or propagation back then.
We use FEC with packet radio, but I doubt mining companies would use that form of digital communication as it requires a computer, keyboard, TNC (Terminal Node Controller) etc.
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Post by dazbt on Jun 17, 2015 15:25:47 GMT -5
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Clive
Shotfirer.
Posts: 168
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Post by Clive on Jun 21, 2015 17:40:47 GMT -5
Back in the 80s the hooker on at the pit bottom at Grimebridge used to take a radio underground. he connected the Ariel to the rails.
Worked a treat, sept you couldnt here it above the noise of the winch.
we also had 3 way walky talkies to between pit bottom, surface, and top level.
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Post by colly0410 on Jul 8, 2015 3:47:39 GMT -5
I'm wondering what modulation system would be best for reflection/multi-path prone underground use: AM, FM, SSB, some form of digital, or even CW? I know the COFDM (coded orthogonal frequency division multiplexing) system used for digital TV in UK is supposed to be very resistant to multi-path, (there are some single frequency networks, can't get much more multi-path than that) so maybe a cut down version of that?
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Post by John on Jul 8, 2015 7:46:26 GMT -5
I'm wondering what modulation system would be best for reflection/multi-path prone underground use: AM, FM, SSB, some form of digital, or even CW? I know the COFDM (coded orthogonal frequency division multiplexing) system used for digital TV in UK is supposed to be very resistant to multi-path, (there are some single frequency networks, can't get much more multi-path than that) so maybe a cut down version of that?
My FT1000MP has the tone generators needed for digital modes and FM "CW", as does my VHF/UHF Ft 736R radio.
Earlier experiments leading to the "Mine Radio" that the NCB developed were FM mode. |
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Post by John on Jul 8, 2015 7:48:56 GMT -5
Back in the 80s the hooker on at the pit bottom at Grimebridge used to take a radio underground. he connected the Ariel to the rails. Worked a treat, sept you couldnt here it above the noise of the winch. we also had 3 way walky talkies to between pit bottom, surface, and top level.
Sorry Clive, couldn't resist..  |
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