Locate underground cable path using FM radio transmitter - Page 1
Forum section: electronics / projects

author: Mugiwara303
author_rank: Contributor
timestamp: October 30, 2020, 07:51:29 am
content: will it be possible and efficient to locate an underground cable by using it as an antenna for a simple fm transmitter circuit and receive the signal with normal radio receiver to locate the path of the underground cable, and will the length of the underground cable as an antenna affect the frequency of the transmitter,Any ideas will be good for me to build one

author: jonpaul
author_rank: Super Contributor
timestamp: October 30, 2020, 08:08:12 am
content: No soil is conductive and will shield FM freq. What is the acess to the cable, is it live? How deep? In a metal conduit?Prof electricians and utilities use low feq not FM band and magnetic detector and not radio.Suggest to search "Underground Cable Location"Typical commercial products:https://www.fluke.com/en-us/products/building-infrastructure/wire-tracersGood luck,Jon

author: Mugiwara303
author_rank: Contributor
timestamp: October 30, 2020, 08:34:32 am
content: i want to locate aluminum armored cable underground that has no power on it it's about 1 meter deep

author: geggi1
author_rank: Frequent Contributor
timestamp: October 30, 2020, 08:48:18 am
content: I know it has been done with AM signals on the LW band.A cable-tracer tuns at about 100khz or lower.

author: Zero999
author_rank: Super Contributor
timestamp: October 30, 2020, 09:57:39 am
content: Quote from: Mugiwara303 on October 30, 2020, 08:34:32 amUse metal detector.

author: calzap
author_rank: Frequent Contributor
timestamp: November 02, 2020, 02:15:32 am
content: If it’s armored with metal (the usual case), you can pretty much forget locating it by injecting a signal or energizing it with AC. Intact armor will block EMR. However, if the armor is aluminum, it may have corroded severely depending on the alloy, coatings and soil conditions, and you might have a chance.Alternate, as Zero999 states, is a metal detector.Mike in California

author: geggi1
author_rank: Frequent Contributor
timestamp: November 02, 2020, 08:32:25 am
content: Quote from: calzap on November 02, 2020, 02:15:32 amOn armored cables the armor must be disconnected at the ends and signal must be injected on the armor. I have done many times and it works perfectly. If the armor is only disconnected in one end you will here the signal at the generator end, but it will be muted very quickly.

author: calzap
author_rank: Frequent Contributor
timestamp: November 02, 2020, 03:24:53 pm
content: Quote from: geggi1 on November 02, 2020, 08:32:25 amI’m not doubting your experience … my cable locating activities have always involved the unarmored types. But, please explain the principle. Typically, the armor on an armored cable is grounded on at least one end. I can see where disconnecting the armor would help with signal injection into the armor in locating the cable where it isn’t buried, like in a wall. But if it’s buried, most of the cable armor except the ends is grounded, so why does disconnecting the armor help? Does the signal disappear into the building ground wiring if the ends aren’t disconnected?Mike in California

author: geggi1
author_rank: Frequent Contributor
timestamp: November 02, 2020, 07:41:09 pm
content: When making the armor floating at the ends and injecting the on the armor the armor becomes the radiator because the signal will go on the outside of the armor. The ground on the injected signal can be put on one of the conductors inside the armor to get the best signal. The armor will basically work as any other conductor when the ends are floating.My experience is when there is a outer layer of plastics or similar to keep the armor isolated form the soil.The signal can even be induktiv injected.The link is for instrument similar to what I have used in the past. Small tracers like the kind used in telecom will not work on buried cables, but might work on cables in a wall depending of the signal level on the generator.https://www.indiamart.com/proddetail/cable-route-tracer-20985143633.html

author: calzap
author_rank: Frequent Contributor
timestamp: November 02, 2020, 11:22:55 pm
content: OK. I understand. If the armor has an insulating coating, then it makes sense.Mike in California