A programmable 36 MHz digital filter bank for radio science

We have designed and constructed an agile eight-channel digital filter bank on a 9U VME board that operates at a maximum clock rate of 36 MHz. A set of these boards has been employed to create 100-200 MHz, 50-100 channel spectrometers. Our applications involve detection of weak signals in a background of noise-pulsar radio astronomy and the search for narrow-band radio emissions from extraterrestrial civilizations. The agility factors include total bandwidth, spacing of filter channels, selection of filter response, and choice of output data format (voltage or detected power). The input is a complex analog voltage centered on zero frequency which is passed to the board via coaxial ports on the front panel. The computational kernels on this board are Harris HSP 43168 Finite Impulse Response (FIR) filter devices. We can also operate the board in a 16-channel output mode. The 2-4 bit format digital output is presented to a custom back plane. Along with our development we have written a suite of simulation software tasks both to determine the sensitivity loss and nonlinear gain response that result from quantization and to optimize filter responses.