Radio suggestion for underground use

[larrybl]

I am looking for suggestions as to the best solution (frequency band, etc) for underground radio communications.
Situation there are several 1/2 to 2 mile underground water pipes, that someone has to transverse, and maintain contact with a person outside. These pipes have several twists and bends, and are constructed of concrete and steel.

We have tried 800 MHz talk around, from the mouth of the pipe, and loose contact within 1/4 to 1/2 mile.

Some locations dead-end, so placeing a radio at each end is not a good option. We would prefer being able to communicate from within the pipe to a person traveling above ground above the pipe.

Permanent solutions (i.e. leaky coax) is not an option, there are too many locations that this would be required, and the water and debris would disable the equipment.

Quick response is necessary during flash flood conditions, for rescue operations.

Hard wire, (field phone) has been discussed, but would like a wireless option.

Any suggestions?
Larry

[N4DES]

You didn't advise what kind of equipment you were using on the surface. If it was a portable I would dump that and go for a higher power mobile radio with a yagi antenna pointed straight down to the gound. I wouldn't go any more than 3 elements so the pattern isn't too tight (but I don't know what your circumference of operation is, but I'm taking a SWAG here). As far as the height above the groud for the yagi, you will probably have to experiment to find the optimum height.

As far as the band, UHF would be my choice due to the efficiency of the portable radio and its antenna. In VHF, the portable radio antenna isn't as efficient (lossy) and the surface yagi is considerably larger in size just in case you have to move it.

[SlimBob]

LF is the only way. Look for what the cavers are using.. stuff runs at 75KHz, iirc...

[larrybl]

Thanks for the reply. We haven't selected any equipment, surface or otherwise. We have tried 800 Mhz in talkaround, currently available radios, with very little success, and forget trying to hit the Trunked system from inside the pipe. As I understand it, these pipes vary in underground debth, and are constructed out of concrete and steel / cast iron sleves. They are anywhere from 48 inches, to big enough to drive a truck in. The folkes that inspect these pipes, and occasionally peform rescue missions, have asked me for suggestions as to how they can keep track of someone while in the pipe. I was hopeing some one out there has had a simular problem, and found a sutable fix. I am aware that radio propragation in general does not penitrate through the ground. One suggestion that may work, is using the pipe as a waveguide and trying lo-band (Caution BatLab Dirty Word comming) 27Mhz CB's.
Just fishing for other thoughts.

[PETNRDX]

We did a little experimenting due to need for SAR in train tunnels, caves, mines, etc.
We did not find any radio band that worked for more than about 1/2 mile.
Higher freqs did better in smaller diameter "holes". VHF didn't work more than several yards.
As the post above says, the 70 to 90 Khz cave radios are the only "wireless" option other than having extra people along the way to "relay" the messages.

[EKLB]

Too bad you couldnt somehow load the rf onto the water pipe itself making it the antenae.

Dont supose you have a 120 volt lighting system instaled through this tunel that you could use the wiring for intercom or the ground as an antnae of sorts at lower freqs?

These are long shots but when desperate they may be the answer for spreading the rf through out the pipe tunel.

Probaby going to be a not so good antenae match but you just might find it works in your situation.

EKLB

[SlimBob]

Another idea might be to do some testing with microwave... I doubt they'd be easy to locate but something operating above 2GHz might be able to bounce around enough... Closer to 5GHz would probably minimize the fresnel zone interference caused by a human.

Get a pair of cordless phones... one on 2.4GHz and one on 5.8 GHz... see how that works.

[kmoose]

Use two code licensed guys, they can tap out Morse on the pipe.

[nmfire10]

Perhaps the tin-can-and-a-string wouldn't be such a bad idea...?

[thebigphish]

Leaky Feeder, will that kind of stuff work?

[larrybl]

Thanks guy's / gal's I got several good suggestions, actually the can and string thing was considered. The main pipe in question is about 2 miles long, and is large enough to drive a truck in. storm drain, no man holes. water can completly fill this durring severe weather, and beleave it or not, kids play, and get traped in it.
We will try 27 mhz with relay people first (immediate fix). and experiment with some Yagi antennas on 800.
I looked at several web sites for Cave Radios, and Mine Communications. Cave dwellers are experimential, and there are no venders of their radios that I could find. Mines use several varations of hard wire and leaky coax, either of whitch would get torn up in a storm drain.

Thanks for the help.

[jhook]

some good reading here on cave radio's and diffrent antenna's


http://www.nckms.org/pdf/putnam-2.pdf - 87k

jhook[/u][/list]

[ro]

Here in austria we have a lot of highway tunnels. Cell phone companies have one way of establishing in-tunnel coverage, that is to install transmitters outside a tunnel and pointing them directly at the hole, so they "beam" right into the tunnel. Works great even for larger distance. We use GSM in the 900 MHz and 1800 MHz band.

[W4WTF]

I'm thinking a 800mhz or UHF base, with a high gain yagi pointed directly into the entrance (I am assuming the entrance is horizontal since you say no manholes) running high power. You should get enough RF bouncing around through the tunnel with a high gain antenna that 2 miles should be good.

In fact, thinking more I would try 900mhz. A high gain (12 element or better) yagi pointed directly in it should have enough gain on receive to pick up. Worst case you can equip the portables with a small 4 element yagi (cushcraft PC904 would be perfect) and definitly make it work. That model is only 9"x7" with another 5 inches of boom behind to hold on to. Shoving 400-500 watts ERP into the opening will definitly get your signal to the end, and the yagi should be sensitive enough on recieve to hear the portables, if not it definitly will be with the small yagi on the portables.

[SlimBob]

There's another leaky-cable like system that uses two parallel wires much like twinlead but farther apart. IIRC, the free-space impedence is either 300 or 450 ohms, so all you need is a balun and some way to tune it...

[nyghthawk]

coming from someone who enters tunnels and such a lot:

The way I see it you have 3 options;

hardline
RF in the end
RF through the overhead.

you already said you wanted wireless

so

RF through the end, you want somethign high frequency and directional (as alrady mentioned 900 MHz or higher with directed elements)

RF through the overhead you either want low frequency stuff (KHz band or lower).

But from my experence with this sort of thing if the tunnels are shallow UHF works better than VHF or 800 MHz.
You might also want to consider higher power than a simple handheld, mobles with a battery and antenna in a packset config?

[ExKa|iBuR]

Larry;

I'm one of said "kids" that likes to "play" in drains, but that's another story. Anyway... Here in Toronto, there are alot of RCP (Round Concrete Pipe) drains, using UHF Jedi's, we can usually go about 500 feet, maybe abit more, until comms drops off completly.

One thing other groups have considered and from what I've heard, works amazingly well...get a UHF mobile with a small gel-cell battery, attatch it to a small yagi (3 or 4 element should be all you'd need) and aim it in. I've heard a 25 watt mobile and portables with decent antennas (read: not stock duckys) can get a good 2 kilometers or so down a drain.

Cave radios around 75kHz work great in natural rock cutouts such as actual caves, they resonate through the rock. They wouldn't work so great in a drain, as most drains are either sheathed in a metal pipe or are of the RCP/SCP (Round/Square Concrete Pipe) design, in which case the material is either too dense to properly work, or it's metal.

I'd stay away from VHF, as it tends not to like going around corners and such. I've never tried 800MHz, but you say it's a no go. UHF would tend to be the best band as it reflects fairly well inside a pipe, and as long as the drain isn't too small, a full wavelength will fit inside it quite well, so its possible the drain itself will act as a waveguide.

Something else you might want to try. I don't know how your system is setup there, but you say you want a guy to walk above ground while someone is below him...in these drains, are there access hatches (manholes) every so often? An idea you might try...
Make a coxial antenna for the band you want to operate on. Attatch it to a length of coax (enough to reach from the surface to inside the drain), then on the other end (surface end), put a decently high-gain antenna (magmount, on the manhole cover, for example). This would work like a passive repeater. It wouldn't give you spectacular results, but it should work alright if you're in reasonably close range to the antenna. Or, if mobility for the person on the surface isn't an issue, just connect the coax right to his/her radio.

Let us know how you make out!

Oh.. The other thing you might consider..

I know it's not wireless, but Telex makes (used to make anyway) something designed specifically for this purpose. It's headsets that are connected to an umbilical cord. The cord is basically a standard rapelling cord with two wires intertwined in it, so it's also a lifeline which you can tie, hook beaners on, etc...

-Mike