Low Frequency Receiver (LFR) Description

Low Frequency Receiver: This covers the frequency range from 1 to 25 Hz using a 2- channel mode of the WFR, specifically using Ex (dipole) and Bx sensors. One waveform series of 512 samples is collected every 32 seconds simultaneously for each of these two sensors. The waveform is spectrum analyzed on board and a 32-channel quasi-logarithmic spectrum is constructed by binning adjacent Fourier components; only 28 of these channels are usable, starting at 1 Hz. The initial AGC gain is set to 20 dB for Ex and 30 dB for Bx and is updated after every waveform series if Auto-Gain-Update has been enabled. The AGC set point is 17, 85; this means on a digital count scale of 0 to 255, there is a factor of 3 "headroom" (255/85)and a factor of 5 hysteresis window (85/17). The RMS signal for each channel is compared to these set-points to determine if the gain should be changed. Sometimes this LFR data can not be collected because of hardware limitations, such as the inability to acquire large snapshots (> 2048 samples) of 80-KHz Wideband data simultaneously with the 100-Hz WFR.