Instrument Options

Ruf et al pdf radiometer

Description (form Ruf et al): The RF bandwidth of 24 MHz is centered on 1413.5 MHz. After the gain and band definition stages, the RF passband is downconverted to an intermediate frequency (IF) range of 15–39 MHz. The ADD backend then samples the IF signal at 110 MHz with a seven-bit signed digitizer. The samples are passed to an FPGA-based DSP module that performs subband filtering, correlations, and histogram digital signal processing. Individual samples of the histograms are generated from 36-ms integration periods.

Each full-bandwidth polarization channel is processed by eight bandpass filters in parallel to divide the 24-MHz input bandwidth into discrete 3-MHz subbands. These filters are efficiently implemented as polyphase finite impulse response (FIR) decimators, taking advantage of the output bandwidth reduction to allow a factor-of-eight reduction in the output sample rate and a corresponding reduction in FPGA resource utilization [3]. The discrete (seven-bit) pdf of each of the eight subbands for both H-polarization and V-polarization is calculated in the subband totalizers, as is done with the full-bandwidth inputs. The power level for each subband, as well as the X-polarization power level, is also calculated in the subband correlators. Every 36 ms, the FPGA initiates a readout operation, during which all of the integrated quantities (pdfs and power levels) are transferred to a command and data handling computer to be recorded for offline analysis.

+ Closely matches GRL results

+ Reasonable data rate

- New gateware

- Few spectral channels

Raw voltage to disk

+ Very flexible

+ Will likely mesh well with new DSN observations?

- High data rate (100 MHz * 8 bits/sample * 2 pols -> 200 MB/sec)

BAPP + Kurtosis

+ Easiest

+ manageable data rate (1 MB/sec)

- Little more work to compare if negative result

+ Alternative method of measuring non-gaussianity would lend some modicum of credibility