A RECEIVE SYSTEM FOR HIGH Q ANTENNAS IN NQR AND A METHOD OF DETECTING SUBSTANCES

A receiving system ( 11 ) for connection to an antenna arrangement ( 19 ) for detecting response signals from a substance having quadrupolar nuclei excited so as to produce nuclear quadrupole resonance in certain of the quadrupolar nuclei. A method for receiving a response signal via the antennae arrangement ( 19 ) is also described. The receiving system ( 11 ) includes an amplifier ( 17 ) to amplify the received response signal from the antenna arrangement ( 19 ) for subsequent processing, a matching section ( 15 ) to match the amplifier ( 17 ) to the antenna ( 19 ), and an isolating switch ( 13 ) to isolate the antenna from the receiving system ( 11 ). The matching section ( 15 ) noise matches the receiving system ( 11 ) to the antenna ( 19 ) during a receiving period to reduce the Q factor of the antenna without significantly degrading the signal to noise ratio. The isolating switch ( 13 ) isolates the receiving system ( 11 ) from the antenna ( 19 ) during a transmitting period when an excitation signal is transmitted by the antenna ( 19 ) to irradiate the substance. It also electrically connects the receiving system ( 11 ) to the antenna during the receiving period immediately after the transmitting period.