Why Your HDD Locator Loses Range: Understanding Active and Passive Interference
A successful horizontal directional drilling (HDD) job should begin with aninterference check. Before you drill, walk the bore path and look for anything that could disturb the locating signal. Most modern DigiTrak, Ditch Witch Subsiteand Radiodetection locators canevaluate external interference at the job site. Signal interference can shorten the usable range of your sonde transmitter and cause variable or unstable readings. The two common categories areactive and passive interference.
Different Types of Interference
Active interference
Active interference is usually caused by electrical noise or background RF energy. Those sources can produce false readings and a fluctuating signal on your HDD locator. Equipment and powered systems near the bore can emit signals that obstruct the radio signal from yourDigiTrak, Ditch Witch Subsite, or Radiodetection transmitter. The most common active sources include:
Radio and telecommunications infrastructure
Power and phone lines
Invisible pet fences
Microwave towers
Underground utilities and other powered or radiating equipment
Passive interference
Passive interference tends toweaken or distort the signal from thesonde transmitter. That can lead to inaccurate depth readings and, in some cases, complete signal loss. Typical passive examples include large metal masses above or below ground, such as:
Rebar and reinforced concrete
Steel pipes
Chain-link fencing
Vehicles parked on or near the line
Salt and water bodies (including domes or saturated zones)
Passive interference is difficult to test for directly. Before drilling, best practice is a thorough site investigation to identify possible interference sources along and around the bore path.
Conclusion
Interference—whetheractive orpassive—can degrade locator performance and reduce confidence in depth and steering data. Starting with awalkover interference check and using modern DigiTrak, Ditch Witch Subsite and Radiodetection equipment to survey the corridor helps crews spot problems early and drill with more reliable steering information.
