Hello list, these days I was experimenting with the FIR filters. If my reasoning are correct there is rooms for improvement with some trade-off between bandwidth flatness and image aliasing. I'm not saying the default FIR is to trash but I think there can be specialized application that will benefit from a custom FIR. Even to just let more people test my theory I need support for FIR coefficient loading so even who can't program the driver but have lab test equipment can give me a feedback. I have prepared a patch for rtl-sdr and gr-osmosdr to load FIR coefficients with a device string like "rtl=0,fir=50:54:57:60:63:65:68:70:72:74:75:77:78:78:79:79"

for a little discussion see here with some screenshot: https://www.reddit.com/r/RTLSDR/comments/5jqk5h/playing_with_rtl2832u_fir_fi...

I'm looking for feedback and once this patch get accepted (I hope so :) ) I will push the one for gr-osmosdr.

best regards Luigi

PS: I hope to not send another garbage patch....

Signed-off-by: Luigi Tarenga luigi.tarenga@gmail.com --- include/rtl-sdr.h | 9 +++++++++ src/librtlsdr.c | 6 ++++++ 2 files changed, 15 insertions(+)

diff --git a/include/rtl-sdr.h b/include/rtl-sdr.h index fe64bea..74cd765 100644 --- a/include/rtl-sdr.h +++ b/include/rtl-sdr.h @@ -169,6 +169,15 @@ RTLSDR_API int rtlsdr_set_freq_correction(rtlsdr_dev_t *dev, int ppm); */ RTLSDR_API int rtlsdr_get_freq_correction(rtlsdr_dev_t *dev);

+/*! + * Load and set FIR filter coefficients. + * + * \param dev the device handle given by rtlsdr_open() + * \param new_fir the vector of 16 integer FIR coefficients + * \return 0 on success + */ +RTLSDR_API int rtlsdr_load_fir_coefficients(rtlsdr_dev_t *dev, int *new_fir); + enum rtlsdr_tuner { RTLSDR_TUNER_UNKNOWN = 0, RTLSDR_TUNER_E4000, diff --git a/src/librtlsdr.c b/src/librtlsdr.c index 9b7ba52..4b7855f 100644 --- a/src/librtlsdr.c +++ b/src/librtlsdr.c @@ -613,6 +613,12 @@ int rtlsdr_set_fir(rtlsdr_dev_t *dev) return 0; }

+int rtlsdr_load_fir_coefficients(rtlsdr_dev_t *dev, int *new_fir) +{ + memcpy(dev->fir, new_fir, sizeof(fir_default)); + return rtlsdr_set_fir(dev); +} + void rtlsdr_init_baseband(rtlsdr_dev_t *dev) { unsigned int i;