GNURadio: Direct Sampling untuk monitoring HF
Sumber: https://www.rtl-sdr.com/rtl-sdr-blog-v-3-dongles-user-guide/
Other software like HDSDR and GQRX can also support direct sampling. It may entail setting a device string, and for the Q-branch, the value should be 2 (or sometimes 3). In GQRX the device string would be
"rtl=0,direct_samp=2"
(without the quotes). In some installs that use different drivers it may be
"rtl=0,direct_samp=3"
instead. Make sure that there is no space after the comma. For SDR-Console please see this linked post for a modified ExtIO that can enable direct sampling. SDR-Touch on Android has a direct sampling option available in its settings page.
To go back to listening to frequencies above 28.8 MHz remember to change the sampling mode back to
"Quadrature Sampling"
Note that this feature makes use of direct sampling and so aliasing will occur. The RTL-SDR samples at 28.8 MHz, thus you may see mirrors of strong signals from 0 - 14.4 MHz while tuning to 14.4 - 28.8 MHz and the other way around as well. To remove these images you need to use a low pass filter for 0 - 14.4 MHz, and a high pass filter for 14.4 - 28.8 MHz, or simply filter your band of interest.
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