This figure shows the block diagram for a OVRO WLM box. The WLM box operates at the ambient temperature and has a system temperature of about 200 K. The rotating mirror can switch between various loads for calibration purposes. After the signal is amplified, it is combined with a 14.2 GHz LO to convert the signal down to 4-12 GHz. The broad band signal is then converted into the three relatively narrow channels illustrated in the previous page using a triplexer. The two continuum channels (C1 and C2) are combined into a single continuum measurement. The Line (L) and Continuum (C) channels are then sent to a detector, and the difference between the two signals (L-C) are then sampled. To remove drifts in the detector and to improve the overall stability of the system, a transfer switch operating at a frequency of 600 GHz switches the Line and Continuum signal between the two detectors. The data are averaged and recorded into a Sybase database system every two seconds.