| 摘要 |
<p>PURPOSE:To improve the S/N of a transmission signal by detecting a noise current invaded in a reception antenna with a noise current detector and using the detection signal and eliminating the noise component invaded in the transmission signal. CONSTITUTION:A reception antenna 11 receiving a transmission signal, a noise current detector detecting a noise current produced by a digging rig 2 and a noise canceller 19 are used to eliminate noise invaded in the transmission signal. For example, a lead wire 23 is led out from a casing pipe 4, an earth rod 24 is imbeded in ground and a current probe (current transformer CT) 25 is provided to the lead wire 23 to measure a branch current in0 flowing to the casing pipe 5 to apply noise cancel processing thereby eliminating the noise. Thus, the transmission signal with excellent S/N is obtained.</p> |
