多个RTLSDR的玩法 [复制链接]

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Spectrum at 1 Hz sample rate of the relative z_1/z_2 phase signal going into two receivers.

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IQ plot of the z_1/z_2 relative phase signal over ~6000 seconds at 1 Hz sample rate

And oh, by the way, I found this nice usb hub, which I'm going to use to hopefully get a 7 channel coherent rtl system.

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Hub with the right usb port orientation for rtl dongles.

Stay tuned for more results. I already have some pretty nice passive radar results using the system, which I'll be posting in a few days.

Update: Apparently three dongles will also run fine from one master clock. I know the clock isn't split correctly, but adding any components would increase the total cost and the whole point of this exercise is to determine what the lower bound is for software defined radios.

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Three channel coherent RTLSDR receiver.

7个RTLSDR的实验，作者主要讨论了多个SDR系统对PC硬件的要求。

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Since they are cheap we can afford several dongles. The utility rtl_eeprom that is a part of the rtl-sdr package can be used to change the serial number so each dongle gets its own serial number. Linrad can then use several dongles simultaneously. Figure 2 shows the screen with 7 dongles running simultaneously on a D5400XS with two 4-core Xeon E5410 processors under Ubuntu 12.04. That computer is now several years old and modern cores are significantly faster. Yet the CPU load is only about 40%. I can not try more dongles, 7 is as many as I have.... Each instance of Linrad uses 40% of one core. Administration (X11 and gnome) uses 63% for a total of 3.43 times one core or 43% of the totally available CPU power.

For unknown reasons Windows is far more CPU hungry. See figure 3.

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Fig. 3. Seven dongles running simultaneously under Windows 7 on a D5400XS computer.

Operation is stable even though the CPU usage is 90%. There is not much resources to run decoders however....

When the dongles are set to produce a small bandwidth it is possible to run several of them on an old computer with just a single CPU core. Figure 4 shows the screen when running 6 rtl-sdr dongles with 240 kHz sampling speed on a PentiumIV computer with the CPU running at 2.66 GHz. Each instance of Linrad uses about 9% of the CPU and the X11 overhead is 29% for a total load of 83%. Gimp which was used to capture the screen is running slowly but it does not cause glitches on Linrad.

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    Fig. 4. Six dongles running simultaneously under Debian Wheezy on a Pentium IV computer.

其他讨论请看原帖。

http://www.sm5bsz.com/linuxdsp/hware/rtlsdr/rtlsdr.htm

实验宽带放大器，用upc1651

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频响测试。

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upc1651频响不够平坦，无法照顾7MHz以下低端。

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输入输出电容使用了22PF，估计小了。

隔直电容直接更换为100nF再看。

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OK，低频延伸不错，1.6MHz在3db范围内。

这曲线，带宽足够玩了。

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