TOP400 Optical Attenuator Universal connector interface (UCI) Less than 2 dB insertion loss The Tektronix TOP400 is a handheld optical attenuator. Its superior design allows it to have less than 2 dB of insertion loss. The TOP400, when used with an optical power meter and source, allows the user to manually dial in attenuation to determine system headroom. It is a passive device and does not require any batteries or power for operation. The TOP400 uses a proprietary scheme for the attenuating mechanism. The small size and large dial indicator make this instrument an indispensable tool for fiber optic line commissioning, bit error rate (BER) measurements, system margin analysis and receiver sensitivity testing. All optical connections are via the precision Universal Connector Interface (UCI) which offers low insertion loss, low return loss and excellent stability.