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.
Matt _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
