Mole Phone?

[Jeremy]

Hello everyone,

Our company is involved in raise boring (vertical tunnel boring). I have heard about a piece of equipment called the "Mole Phone" that cavers use.

Does anyone have any details about it? Who makes it? Etc. It would greatly assist our underground operations if it was suitable.

Many thanks,


JT.

 

[Mine Explorer]

<snip> I have heard about a piece of equipment called the "Mole Phone" that cavers use.

Does anyone have any details about it? Who makes it? Etc. It would greatly assist our underground operations if it was suitable.

As I understand it, the "Mole Phone" is no longer obtainable as a number of critical components have gone obsolete. It was because of this that the HeyPhone project came into being.

For more information on the HeyPhone try visiting http://www.heyphone.org

The unpopulated circuit boards for the HeyPhone are available for you to build your own version. Neither the Heyphone or Mole Phone are available commercially (AFAIK)

 

[Jeremy]

Thanks a lot.

It suprises me that a wireless underground communication system is not commercially available.

Does anyone know how well they work and the maximum range? I suppose the conditions have a great deal to do with this.

 

[cap n chris]

Jeremy's right about range - it depends!

From practice rescues my understanding is that Heyphone range is under 1km but it is possible to use "relay" stations (i.e more than two units). When they are rigged correctly (with aerials contacting wet rock and lined out neatly) the comms quality is good but narrow bandwidth.

Low frequency magnetic induction is how they work, apparently, but I'm not a techie. Why not come along to a cave rescue practice and use one for real? BTW, what's your proposed application? - if it's line of sight comms I'd just use a cheapo two way radio.

 

[Mine Explorer]

Does anyone know how well they work and the maximum range?

That's pretty variable. If the rock between the two stations is all the same type then the range can be impressive. If you have different kinds of rock strata then the range is reduced.

If you have specific requirements/questions concerning your situation then it would be worth contacting CREG. There is a wealth of experience and knowledge available. CREG members have taken HeyPhones to various working mines, show mines/caves and tunnels to carry out experiments and demonstrate HeyPhone performance.

 

[Mole]

It suprises me that a wireless underground communication system is not commercially available.

http://www.infomine.com/index/suppliers/MineCom_International.html

 

[paul]

BTW, what's your proposed application? - if it's line of sight comms I'd just use a cheapo two way radio.

Re line of sight and two-way radiois: DCRO are experimenting with using coax cable to "pipe" the waves connecting 2 PMR radios. So far results are good with comms between 2 PMRs excellent even though each were separated by some distance and quite a few bends in the passage. I presume this would also help in shafts where line of sight wasn't available.

 

[Dave H]

Coax? If you're going to all that effort, surely it would be simple to run out a length of cheap, light and flexible figure of 8 cable and use it with a telephone type system?

As mentioned before this really is the realm of CREG. I was (am?) a member, but when it came to some of the physics of radio transmission through rock it all became too complex for me to be bothered to read. Don't get me wrong, it's great work, just not of huge interest to me. There are many brilliant contributers to CREG but I think the guru is D ave G ibson. 8)

 

[mudmonkey]

DaveH - as far as I understand it, the advantage of the coax system is that you can use handhelds within a few feet of the cable, rather than having to plug anything in.

 

[Stu]

Coax? If you're going to all that effort, surely it would be simple to run out a length of cheap, light and flexible figure of 8 cable and use it with a telephone type system?

As mentioned before this really is the realm of CREG. I was (am?) a member, but when it came to some of the physics of radio transmission through rock it all became too complex for me to be bothered to read. Don't get me wrong, it's great work, just not of huge interest to me. There are many brilliant contributers to CREG but I think the guru is D ave G ibson. 8)

It became too complex for you?! Thought you were the brains of the forum!! Must be complex...

 

[Mine Explorer]

Coax? If you're going to all that effort, surely it would be simple to run out a length of cheap, light and flexible figure of 8 cable and use it with a telephone type system?

Well. Cheap, light, flexible figure of 8 cable can also be used as a leaky feeder.

Although we haven't used it with PMR446, fig. 8. cable has been used successfully at 27MHz over great lengths. If the signal strength is poor then it's possible to wrap a couple of turns of the cable around the radio antenna.

Really it all depends on your situation as to whether it's worth the effort of laying a cable, be it a leaky feed or a field phone.

 

[Dave H]

Thought you were the brains of the forum!!

Oh Stu, you shouldn't !

 

[paul]

Coax? If you're going to all that effort, surely it would be simple to run out a length of cheap, light and flexible figure of 8 cable and use it with a telephone type system?

Well. Cheap, light, flexible figure of 8 cable can also be used as a leaky feeder.

Although we haven't used it with PMR446, fig. 8. cable has been used successfully at 27MHz over great lengths. If the signal strength is poor then it's possible to wrap a couple of turns of the cable around the radio antenna.

Really it all depends on your situation as to whether it's worth the effort of laying a cable, be it a leaky feed or a field phone.

I don't know how the decision to opt for coax came about (or even what fig. 8 cable is - unless you mean an ordinary length of insulated copper cable) or whether any other types of wire/cable were considered.

On a recent exrecise we were using a length of thin coax (60m) with a "dipole" at each end (also made from coax). My end of the coax was well out of sight of the other end and the entire length of cable was run out. I was able to communicate with somebody on a PMR near the dipole at their end while I was some 25m away from the dipole at my end and around several bends in a large passage. After disconnecting the dipole at my end I had to be near the end of the coax to get any connection at all. When I was able to communicate the reception was loud and clear at both ends.

The reason this is being tried out is to assist with shaft comms and also to connect a Heyphone position with another area not too far away but out of line of sight. Use of cable/dipole means there is still some flexiblility in position unlike with a filed telephone setup (where you would have to be stationed ear to the end of the cable).

 

[Dave H]

A ladder down a shaft acts as a very good wave guide. ldgit:

Figure of 8 cable is sold primarily for wiring speakers. Two 'wires' are sheathed and the sheaths are joined (hence the figure of 8 shape) It costs about £11 for 100m for the 13/0.2mm 2A stuff. Which is much cheaper than coax. It also has the advantage of being unshielded, which means that you should get the benefits of the wave guide just from being near it, not just at the ends.
To use your application as an example, this would allow continuous communications, say with a stretcher party, along the entire length of the wave guide.
If I'm miss-remembering my data comms theory from 20 years ago then I appologise. But I would suggest talking to the guru I mentioned before.

 

[paul]

Thanks Dave - I'll pass your suggestion on to try Figure 8 cable as well. Presumably a single wire will work as well as the twin configuration of speaker cable? Or maybe the twin wires have a stronger effect??

 

[Dave H]

Presumably a single wire will work as well as the twin configuration of speaker cable?

I don't know. Twin has the advantage that it could be used additionally for a telphone system. That's why it's permanently placed in Darren entrance crawl, etc.

 

[Mine Explorer]

Presumably a single wire will work as well as the twin configuration of speaker cable?

I don't know. Twin has the advantage that it could be used additionally for a telphone system. That's why it's permanently placed in Darren entrance crawl, etc.

...although a single wire could also be used with a telephone system, so long as it's a 'single wire' telephone.

 

[twllddu]

Has anyone any experience of using the cheapish (~£50) two way radios in shafts over about 150m ?

 

[Mine Explorer]

Has anyone any experience of using the cheapish (~£50) two way radios in shafts over about 150m ?

150m = 490ft

Mmm, nah, sorry.

We were using 'el cheapo PMR446s in a 220ft mine shaft last weekend, but that does have an 8" cast iron rising main, steel ladderways, steel pump rods etc. going the full length - so they'll help a lot as well.

 

[Duncan]

Has anyone any experience of using the cheapish (~£50) two way radios in shafts over about 150m ?

We used cheap PMR446 radios to communicate on a 284m pitch while taking this photo, which has been posted to this forum before, but here it is again:


(click image for larger view)

The distance from the photographer to the guy with the upper flashgun was 200m, and communication was OK, but as you can see there was a good clear line of sight.

Duncan