05621325 is referenced by 60 patents and cites 8 patents.

An apparatus and method is provided for determining if the signal received from an underground beacon (10) at a locator (22) is a true signal or a ghost signal. Orthogonal horizontal antenna (38) and vertical antenna (40) are used and a ratio is computed of the signal strengths measured by the two antennas. At the true location, the signal strength in the horizontal antenna (38) will be maximum and the signal strength of the vertical antenna (40) will be a null. If the ratio of the signal strength sensed by the horizontal antenna and vertical antenna is large, exceeding a predetermined value, the locator is receiving a valid signal from the beacon and a display of this fact is made on a display on the locator and the depth of the beacon is calculated. If the ratio is less than the predetermined value, a ghost signal is being received and this fact is displayed on the display on the locator (22).

Title
Avoiding ghosting artifacts during surface location of subsurface transmitters
Application Number
8/442487
Publication Number
5621325
Application Date
May 16, 1995
Publication Date
April 15, 1997
Inventor
Jian J Jin
Perry
OK, US
Michael F Gard
Perry
OK, US
Frank S Nickel
Perry
OK, US
Gregory W Draper
Perry
OK, US
Agent
Sidley & Austin
Assignee
The Charles Machine Works
OK, US
IPC
G01R 19/145
G01V 3/11
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