Cor-Tek Power, LLC

HDD: Active and Passive Interference and What It Means for your Jobsite

Posted by Benjamin Nickel on

When you're working with underground drilling, there are an abundance of variables you will need to look into. Between the pre-site planning and Geotechnical reports and setting up the proper equipment needed, the one thing that tends to get in your way is the Active and Passive Interference with your DigiTrak Transmitter, Ditch Witch snode, and Subsite snode.

One of the most important devices you need on a HDD worksite is a working Transmitter. This transmitter emits a magnetic field directly behind the cutting head that is read by the receiver at the ground surface. Like all other transmitters, other devices at the jobsite can interfere with the signal and cause the receiver to misread the input.

Active Interference

Active interference refers to the electrical interference or background noise on a site. A common definition is “Anything that emits a signal or generates its own magnetic field”. Things like radio’s, Telecommunications, power and phone lines, Invisible pet fences, underground utilities, and microwave towers all have an effect on the surrounding area. Active interference affects any device that is emitting a radio signal like those for your DigiTrack transmitter, Ditch Witch and Subsite snodes.

Possible signs of Active Interference are erratic signal strength and depth readings, depth errors from loss of pitch and roll data, and inaccurate calibration.

Passive Interference

Passive Interference is almost the exact opposite of Active. It is referring to the objects located at the site that will stop or distort the signals you are trying to read. “ Anything that blocks, distorts, or absorbs a magnetic field.” A common passive example are metal structures such as chain link fences or rebar, and salt water. Unfortunately, anything that is conductive can act as passive interference.

Signs of Passive Interference is your depth appearing greater or shallower than they actually are. You can also get an incorrect drill head location and direction. And one of the most frustrating signs is you get no data at all, all signals are blocked.

What can you do to minimize the impact

The first, and most important, thing anyone can do for a HDD worksite is to walk the path of the drill before starting. Have your receiver turned on and look for any signals it picks up. The stronger the signal present, the greater the interference level. This allows you to gauge when and where you will end up with a possible snag in operations.

A second step is to simulate the interference. Carry the transmitter so that it is 1.5 times the anticipated drill depth from the receiver (Which is walked down the borepath). If the pitch and roll information is not affected during the test, then it's a good indicator that you should be clear for the real thing.

If you see interference and want to try to minimize its impact, go take a look around. Is there something you can turn off? Security systems and invisible dog fences are possible items that can be shut down for the time you're actively drilling. Another way is to get a stronger transmitter that can overcome the interference.

If you are looking for the proper Digitrak transmitters and snodes, Subsite beacons, batteries, or chargers for any Drilling worksite, Cor-Tek Power is there to help. With over ten years in the Direction Drilling and Boring equipment field, we understand the needs of your HDD project. With warranties available that outlast even those offered by DCI, we keep rebuilt transmitters in stock and ready for expedited availability. Downtime on a worksite is both time and money lost. Give us a call at 888-374-0382 or visit us at

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