RTL-SDR source in GNU-Radio 3.7.1 weird behaivour at 900 ksps
Hi again. I noticed a strange behaivour from RTL-SDR source in GNU-Radio 3.7.1 When sample rate is set to 900ksps, actual output sample rate is only 300 ksps. You can check this easily connecting a RTL_SDR Source to a WX Gui FFT Sink and a RF signal generator. For example, on RTL-SDR Source set sample rate to 900000 and frequency to 144000000 Hz. On the WX GUI FFT Sink, set sample rate to 900000 and base frequency to 144000000 Hz. Now apply a signal on 144.1 MHz. The FFT Display will show it at 144.3 MHz. Apply a signal on 144.05 MHz. The FFT Display will show it at 144.15 MHz. Now on the WX GUI FFT Sink, set sample rate to 300000 and repeat the above steps. The signal will be displayed at its right places. Interestingly, setting sample rate to 1Msps works fine. Tested with both E4000 and R820T dongles. Any advice? Thank you!
Any advice?
Stick with what works. The driver will accept any sample rate and ask the RT2232 for it ... but since there is no real documentation, there is no way to know if that will really work or create issue inside the RTL2232 chip ... That's the problem with using stuff in ways they weren't design for. For consistent results, you should stick with commonly used samples rates like 1M 1.024M 1.2M 2M 2.048M 2.4M Avoid things lower than 1M and avoid weird, not-often used, values. Cheers, Sylvain
*>>> For consistent results, you should stick with commonly used samples* *>>> rates like 1M 1.024M 1.2M 2M 2.048M 2.4M Avoid things lower than 1M* *>>> and avoid weird, not-often used, values.* Thank you Sylvain. I thought 900 ksps was one of the standard rates in the RTL2832 chip, so that's why I used it, to keep cpu usage low because my application must work in a Intel Atom N270, the smallest one. In fact I used many times 900ksps with GNURadio 3.6.x without any problem at all. I'll use 1Msps for now.
Hello Miguel, In Linrad I have these defines: #define MAX_RTL2832_SAMP_RATE_H 2400000 #define MIN_RTL2832_SAMP_RATE_H 900001 #define MAX_RTL2832_SAMP_RATE_L 300000 #define MIN_RTL2832_SAMP_RATE_L 230000 900 kHz does not work, try 900001 Hz. The range 300001 to 900000 Hz does not work with RTL2832. 73 Leif A. Vallejo" <ea4eoz@gmail.com> wrote:
Hi again.
I noticed a strange behaivour from RTL-SDR source in GNU-Radio 3.7.1
When sample rate is set to 900ksps, actual output sample rate is only 300 ksps.
You can check this easily connecting a RTL_SDR Source to a WX Gui FFT Sink and a RF signal generator.
For example, on RTL-SDR Source set sample rate to 900000 and frequency to 144000000 Hz.
On the WX GUI FFT Sink, set sample rate to 900000 and base frequency to 144000000 Hz.
Now apply a signal on 144.1 MHz. The FFT Display will show it at 144.3 MHz.
Apply a signal on 144.05 MHz. The FFT Display will show it at 144.15 MHz.
Now on the WX GUI FFT Sink, set sample rate to 300000 and repeat the above steps. The signal will be displayed at its right places.
Interestingly, setting sample rate to 1Msps works fine.
Tested with both E4000 and R820T dongles.
Any advice?
Thank you!
Oooops! I forgot the "one" in 900001 Thank you, and sorry for the inconveniences
participants (3)
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Leif Asbrink -
Miguel A. Vallejo -
Sylvain Munaut