Radio comms in a large water pipe 1

[NZtech]

I have need to provide a communication system for a company building water pipe lines. The pipes are typically 1.2 meters in diameter, and follow the terrain of the land. There are men working inside the pipe (up to 2km up the pipe) who need radio comms to the end. Any suggestions would help. I thought maybe using the pipe as a wave guide for 150 Mhz, but have no idea if this would work.

 

[jbartos]

Suggestion: Visit

http://www.grainger.com

and type Communication in Advanced Search, and then Two-way Radio,
which will return Motorola, Jobcom, Brady manufacturers

 

150 MHz is 2m wavelength, your pipes are 1.2m diameter. I can't find the equation for "waveguide beyond cutoff" right now, but I suspect that a 2m wavelength is too big to fit into your pipeline. Give it a try based on available equipment, but if you have no luck with your VHF (150MHz) walkie-talkies, try some UHF walkie-talkies before you give up. I would guess that UHF walkie-talkies would work in that situation. Good luck.

 

To paraphrase the ARRL UHF/Microwave Experimenter's Handbook, published in 1990, page 5-29:

The dominant mode of propagation in a circular waveguide is TE11... The guide will exhibit a cutoff wavelength equal to its diameter times 1.706 (~ square root of 3).

Lambda cutoff ~ 1.706 * diameter = 1.706 * 1.2 = 2.05m
Lambda of 150MHz is 2m (seems like you knew all that!).

It is pretty close to cutoff. There might be sufficient variation (bends for example) to put it below the limit. If it doesn't work, then move up to UHF.

 

[proff]

Although waveguide method will work in theory, it is an unreliable route for this problem.
Perhaps the most reliable route is to run a length of leaky coax from a base station throughout the length of the pipe and transmit to and receive from this cable using low cost short range transmitters.
If you want more details, let me know. ian.proffitt@baesystems.com

 

[jbartos]

Suggestion: The transmitter radiated power should not be overlooked. It shall be considered with the wavelength. 1 or 2 Watts of radiated power of inexpensive mobile transmitters will not be enough.