On Fri, Oct 23, 2009 at 7:08 PM, Matt Ettus <m...@ettus.com> wrote: > John Orlando wrote: >> >> Hi all, >> I was just reading the specs/schematic on the LFRX RF daughterboard, >> and noticed that the literature indicates that there is a 30 MHz >> low-pass filter after the differential amplifiers. Looking at the >> schematic, there is a 50 ohm resistor + 20 pF capacitor on each leg of >> the differential amplifier output. I believe this would mean that, >> for each of the differential amplifiers, the effective resistance is >> really 100 ohms (two 50 ohms in series) with 10 pF (two 20 pF in >> series). If it really is 100 ohms + 10 pF, the passband of the filter >> is much larger than 30 MHz. Even taking into account some input >> capacitance on the A/D converter on the USRP (10-20 pF?), it still >> would be larger than 30 MHz. Am I missing something here? > > > The caps on each leg are 82pF, or 41pF in series. That gives a 3dB > bandwidth of about 38 MHz.
Thanks Matt...I'm looking at the LFRX schematic found here: http://gnuradio.org/trac/browser/usrp-hw/trunk/basic-lf/lfrx.pdf Is there a more up-to-date version I should be looking at? This one still shows the 20 pF caps instead of the 82 pF caps. Regards, John Orlando www.epiq-solutions.com _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
