I have to start with an errata corrige: my laptop has Windows 8.1 and not 7, which is installed on another computer. Anyway, I've done some tests with a RTL-SDR, and I can definitely say that something goes wrong. When I start the rtl-test sometimes a peak appears at the correct frequency (e.g. if i set sampling at 100 MHz i find a peak at 3*100 - 50 = 250 MHz) and then disappears less than a second after; most times it doesn't even appear at all. I've also tried running fl2k_test on Linux with a live DVD of Ubuntu 18.10 and everything seems to go well: it runs correctly even at high sample rates (150 MS/s), spewing out just an error on zero-copy buffers. Here is a log: ubuntu@ubuntu:~/osmo-fl2k$ fl2k_test -s 150e6 Allocating 6 zero-copy buffers libusb: error [op_dev_mem_alloc] alloc dev mem failed errno 12 Failed to allocate zero-copy buffer for transfer 4 Falling back to buffers in userspace Reporting PPM error measurement every 10 seconds... Press ^C after a few minutes. real sample rate: 149990146 current PPM: -66 cumulative PPM: -66 real sample rate: 150001491 current PPM: 10 cumulative PPM: -28 real sample rate: 150009752 current PPM: 65 cumulative PPM: 3 real sample rate: 149996142 current PPM: -26 cumulative PPM: -4 real sample rate: 150012666 current PPM: 84 cumulative PPM: 14 real sample rate: 150001814 current PPM: 12 cumulative PPM: 14 real sample rate: 150003433 current PPM: 23 cumulative PPM: 15 real sample rate: 149999114 current PPM: -6 cumulative PPM: 12 real sample rate: 149999349 current PPM: -4 cumulative PPM: 10 real sample rate: 150014477 current PPM: 97 cumulative PPM: 19 real sample rate: 149995547 current PPM: -30 cumulative PPM: 15 real sample rate: 150008611 current PPM: 57 cumulative PPM: 18 real sample rate: 149994234 current PPM: -38 cumulative PPM: 14 real sample rate: 150004040 current PPM: 27 cumulative PPM: 15 real sample rate: 150011047 current PPM: 74 cumulative PPM: 19 real sample rate: 149990169 current PPM: -66 cumulative PPM: 13 real sample rate: 150008286 current PPM: 55 cumulative PPM: 16 real sample rate: 149999384 current PPM: -4 cumulative PPM: 15 Using my RTL-SDR I find the peak at 3*150 - 75 = 375 MHz, as expected. I will run some other tests on my other computer, the one with Windows 7. Have a nice evening, Francesco -- Francesco Gugliuzza