a however if the antennas 122 123 are configured such that at least one antenna is axial or transverse fig4 b 4f while useful information may be had not all nine components can be determined for example if the antennas 122 123 are transverse as illustrated in fig4 b the coupling components that can be determined are limited to xx xy yx and yy this can been seen by substituting u03b2 90 u00b0 into equation 1a the embodiment of fig4 g because of the radial offset of transmitter antenna 123 does yield all nine components though equation 1a would have to be slightly modified to account for the offset in u s patent no 6 509 738 by minerbo et al the use of offset parallel antennas is described the derivation above assumes rotation of the bha 100 and a relative rotation between an upper portion of bha 100 and a lower portion of bha 100 the rotation angle of the upper portion of bha 100 is u03c6 and the relative rotation angle of the lower portion of bha 100 is given by the angle u03b1 however certain drilling operations such as directional drilling have drilling modes in which the upper portion of bha 100 substantially does not.