Birdies in the pdev device (narrow band) 03jul07 Previous data taken with the pdev spectrometer used the "sp1" fpga code and a temporary mixer chassis. The "sp1" code gave 20Khz channel widths (hires is not yet installed) while the mixer chassis cut out a few hundred Khz about dc. On 03jul07 data was taken with the "radar device" that tamara is working on. It uses the pdev spectrometer with fpga code that filters the data and then writes the time samples out to disc. The version used was still in the development stages. This data set allowed us to look at birdies close to dc that may be coming from the switching power supply. The setup was: * pulsar noise src used to generate the noise. * The noise was passed through at 25 Mhz lowpass filter. This filter less than .5 db drop from 0 to 10 Mhz. * Data was sampled at 156Mhz (internal clock) using a single digitizer. * The data was filtered and decimated by 8. It was symmetric since we only took I rather than I and Q. * We were limited to 1 seconds worth of data per file (this will be corrected shortly). 120 files were taken. * The spectral density was computed from the data and then averaged for the 120 seconds of data. Resolutions of 595 and 19 Hz were used. The plots show the averaged spectral density (.pdf) <./pdevSpc_03jul07.pdf>: ------------------------------------------------------------------------ ------------------------------------------------------------------------ processing: x101/070703/chkfile.pro <- page up home_~phil