Rejection of radio-frequency noise with a wide-band differential preamplifier and solid-shielded coaxial input cables

Conference · Wed Jan 01 04:00:00 EST 1975

OSTI ID:4152291

Burns, R S; De Lorenzo, J T

Radio-frequency signals simulating electrical interference ranging from 50 Hz to 50 MHz were applied to the shields of the input cable system (two solid- shielded, mineral-insulated cables approximately 6 m long) of a wide-band (approximately 60 MHz) differential preamplifier for use with fission counters as input devices as part of in-vessel, low-level flux monitors in future liquid- metal fast breeder reactors (LMFBRs) to determine the common-mode rejection. Results show that differences in electrical properties and shielding characteristics of the two input coaxial cables along with end effects produced by an unbalanced sensor severely degrade the rejection capability of the differential preamplifier. At 1 MHz, the common-mode rejection without input cables is approximately -70 dB; this is reduced to approximately -10 dB when measured with the rf signal applied to the surface of the input cable shields. Measurements of the shielding characteristics of the input cables showed resonances at test frequencies greater than 2 MHz. A ferrite core was installed in the input assembly to increase the impedance of the shields and to permit termination of the coaxial line consisting of the input cable shields and the protective metal conduit for the input cables. This assembly eliminated all resonances below 20 MHz. The increased impedance also reduced the amplitude of the shield currents, resulting in an increase in the shielding effectiveness of the input cables without affecting the signal transmission of the cables. (auth)

• Research Organization: Oak Ridge National Lab., Tenn. (USA)
• NSA Number: NSA-33-007361
• OSTI ID: 4152291
• Report Number(s): CONF-751116--6
• Country of Publication: United States
• Language: English

Related Subjects

*FISSION CHAMBERS-- NOISE
*NEUTRON DETECTION-- FISSION CHAMBERS
440101* --Instrumentation--Radiation Instrumentation-- General Detectors & Monitors
COAXIAL CABLES
INTERFERENCE
LMFBR TYPE REACTORS
N46110* --Instrumentation--Radiation Detection Instruments-- General Detectors & Monitors
NEUTRON FLUX
PREAMPLIFIERS
RADIOWAVE RADIATION
SHIELDING