Best way to locate a pipe underground with a radio beacon  - Page 1
Forum section: electronics / projects

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: April 24, 2021, 04:37:56 pm
content: Dear All,They are installing optic fiber connection in my village. Unfortunately, the guy who came was not able to pass his fiberglass rod in thee existing pipe. The distance from the house to the street is 100m and there is an existing pipe which is about 4 cm diameter, but impossible to know where it is supposed to pass and where it arrives in the street.After many attempts, I would try to locate the location of the pipe in order to dig some intermediary pits. Say every 25 m. For this I imagine to send a small beacon with a fiberglass rod and locate the pipe by searching for the maximum level or radio emission. The pipe is buried about 80 cm underground. It is a plastic pipe.I imagine using a HC-12 emitter or a lora emitter, but I want to keep it as simple as possible ( no additional MCU) as it has to fit in the pipe. and the best is to push it as far as possible.Do you think this is possible ?What are the best options ?Thanks for any suggestion.

author: jmelson
author_rank: Super Contributor
timestamp: April 24, 2021, 05:27:34 pm
content: I assume you have access to at least one end of the conduit. If you have access to both ends, do you have an air compressor? How about a garden hose? Assuming dirt, etc. has plugged up the hose, use water or air to blow it out. Then, use a shop vac to suck a "parachute" and string through the conduit. Then, you can use the string to pull the fiber through.Jon

author: Gyro
author_rank: Super Contributor
timestamp: April 24, 2021, 05:39:19 pm
content: I remember similar questions coming up in the past.Forum searches for 'underground pipe' and'underground cable'[Edit: I see it is plastic] bring up a few threads which might give you some applicable ideas.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: April 24, 2021, 07:11:57 pm
content: Thanks for your answers@jmelson :I have tried with an air compressor to locate which pipe was the right one in the telecom pit in the street. But this failed. My compressor is reasonable ( 50 l reservoir), but after making some rapid computation it is quite understandable that it failed. The hose of the compressor is 1 cm diameter. The telecom pipe is 4 cm. So the ratio of the surface is 1/16. If you put 4 bars at the entrance, it is only 1/4 bar in the pipe. Moreover , over 100 m everything is lost. Most probably also the old pvc pipe ic clogged.It was a nice try, but it failed.@Gyro :Yes, I am not trying to locate a metal pipe underground, but a PVC pipe.I will make a try with a keyfob at 433 Mhz and a Hackrf-portapack as a receiver. Will see if it works. I have tuned an antenna so it is adapted to the keyfob frequency ( 434 Mhz). I have now to solder a small switch on the keyfob so it remains always ON, and hopefully will have a try tonight just to see if the emission can go through 80 cm of soil ( mostly sand).

author: Jeroen3
author_rank: Super Contributor
timestamp: April 24, 2021, 07:59:18 pm
content: Find your local equipment rental place (like boels) and rent one of their "underground pipe detectors with generator".If the pipe is already carrying a metal cable you can also use that to detect it.I supposed this is much easier than diy-ing a locator.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: April 24, 2021, 08:01:11 pm
content: I just made the experiment, sending the keyfob about 5 m in the pipe. Then going outside, I clearly got the signal on the harckrf.But it is not very easy to locate the maximum of reception. I must say I am not familiar at all with the portapack/hackrf. Also my antenna is well tuned, but it is a 1/4 wave ground plane antenna . Maybe I should make a Yagi antenna.

author: perdrix
author_rank: Frequent Contributor
timestamp: April 24, 2021, 08:05:30 pm
content: Dowsing with a couple of bent brazing rods works quite well too!D.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: April 24, 2021, 08:21:14 pm
content: Sure ! But for this to work, you need to have faith, which I have not .

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: April 24, 2021, 08:25:24 pm
content: Quote from: Jeroen3 on April 24, 2021, 07:59:18 pmThat may be a final try, but to search with some DIY method will help to identify which professional tool may be useful.For example, I also tried to send a signal on a pair of wires not used in the existing telecom cable, but it seems that the cable is shielded, or maybe it is because they are twisted pairs, but there was not much emission from the cable. This si why I decided to send a dedicated emitter.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 24, 2021, 08:43:54 pm
content: Quote from: AlcidePiR2 on April 24, 2021, 08:25:24 pmTry sending a common mode signal on that cable with respect to ground. A modulated signal in the AM band is easily done with a function generator and a common AM radio would work as the receiver.

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2021, 06:14:50 am
content: the FCC gives you some leeway for cable locating equipment actually, if you read section 15

author: SeanB
author_rank: Super Contributor
timestamp: April 25, 2021, 08:54:10 am
content: Existing ccable you simply use a 4-5W Rf transmitter, probably around 13MHz, which is in the ISM band, and a loop antenna for the receiver. Loop antenna is small at 13MHz, so will detect well. The air hose to blow through the pipe is better, you have to block off the house end, with the pipe in there (rags soaked with water stuffed into the hole, and rammed tight work well) and blow the air through, which at least gets you to which pipe in the pit is yours. then you use a heavy fishing line, with a long flag of rag attached to the end, and blow it through, using a small diameter pipe to pass through the rag fill. Thin pipe just a bit bigger in diameter than the line, so the air loss is not too bad, and you will get the flag at the pit after a few minutes. When pulling the fibre optic cable back attach a second fishing line to it as well, so as to leave a pull for any further cable upgrades.If the compressor you use is not enough air flow rent one for a day, it is a lot cheaper than trying to dig up 100m of yard and lay a new conduit.

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: April 25, 2021, 09:31:01 am
content: Thanks SeanB, but for the compressor, owing the very little success we had, I believe the pipe is clogged. The problem is that we are in wood area. There are many trees and roots. Of course I can rent a larger compressor, but this will be if nothing else works.In any case, we need to locate the path of the pipe in the property to be able to dig an intermediary pit.Maybe as you say the RF signal is a good try. I have already tested, with a cable tester like this onehttp://www.360idcom.fr/Quality-Network-Cable-Tester-Line-Finder-21919/Computers-Tablets-&-Network-Hardware.shtmlbut this was not very useful. We actually detected the signal in the telecom pit, but as all wires are connected together we could not deduce which one was the right one.On the other hand, I should, as you say use this technique to detect the path of the cable. At the beginning I used a twisted pair, but the emitting radiation is then much reduced. I think I can use a send pair so maybe in this case use both wires on each pair as a single cable. This should be better.What are your suggestions for sending a 5W. 13 Mhz signal in these wires ?Thanks

author: jonpaul
author_rank: Super Contributor
timestamp: April 25, 2021, 10:39:37 am
content: Bonjour AlcidePiR2,je connais très bien cette problem, et j'ai trouvée quelques solutions depuis 2005.1/ The usual cause is a break in the conduit by tree roots or nearby digging and constructions.2/ Easiest to trace starting at the building connection rather than the streen utility box.3/ RF cannot penetrate soil, especially sandy and damp as the soils act as a shield.4/ The professionals find the path by first disconnecting the phone or other cables, then binding all conductors TP, shields together into ONE circuit.They use a LOW FREQUENCY oscillator from earth ground to ALL the cables (common mode) together.5/ The magnetic filed is detected by a loop, NOT the EM field.The loop is directional and can be nulled to precisely locate the cable. RF methods will never be precise.6/ We have used a simpler method: A thick wire (or plumber "snake) is threaded into the conduit and moved forward until it is blocked. Mark the position of the cable with tape.Withdraw, measure distance to end, = distance from entrance to blockage.Pace out and dig!7/ We discovered the 40 mm thick PVC conduit had been totally shattered by concrete work after it was installed, the concrete installer used a power vibrator machine to compact the earth that broke up the conduit.Bon Chance,Jon

author: AlcidePiR2
author_rank: Regular Contributor
timestamp: April 25, 2021, 01:23:53 pm
content: Quote from: jonpaul on April 25, 2021, 10:39:37 amHere it is most probably trees roots as there are no constructions in the vicinityQuoteBut I was quite succesful with my keyfob at 433 Mhz. Not so easy to pick precisely the place, but sufficient to havea good idea of where the pipe is. It was not at all in the direction we expected but like this we could only go about 7 m in the pipe.QuoteThis will be my next move to track the pipe on all its length. What frequency to use ? at which power ? how to build the receiver ? what kind of antenna ?QuoteOf course, this is what we planned to do but first you need not only to now the distance of the first clogged place, but also the direction. This is what we are searching with the beacon or the radio emission of the wire .