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多个RTLSDR的玩法 [复制链接]

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只看该作者 60楼 发表于: 2014-04-13

Spectrum at 1 Hz sample rate of the relative z_1/z_2 phase signal going into two receivers.
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只看该作者 61楼 发表于: 2014-04-13

IQ plot of the z_1/z_2 relative phase signal over ~6000 seconds at 1 Hz sample rate
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只看该作者 62楼 发表于: 2014-04-13
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.

Hub with the right usb port orientation for rtl dongles.
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只看该作者 63楼 发表于: 2014-04-13
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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只看该作者 64楼 发表于: 2014-04-13



Three channel coherent RTLSDR receiver.
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只看该作者 65楼 发表于: 2014-04-13
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。

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.
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只看该作者 66楼 发表于: 2014-04-13
For unknown reasons Windows is far more CPU hungry. See figure 3.

Fig. 3. Seven dongles running simultaneously under Windows 7 on a D5400XS computer.
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只看该作者 67楼 发表于: 2014-04-13
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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只看该作者 68楼 发表于: 2014-04-13

    Fig. 4. Six dongles running simultaneously under Debian Wheezy on a Pentium IV computer.
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只看该作者 69楼 发表于: 2014-04-13
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只看该作者 70楼 发表于: 2014-04-15
实验宽带放大器,用upc1651
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只看该作者 71楼 发表于: 2014-04-15
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只看该作者 72楼 发表于: 2014-04-15
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只看该作者 73楼 发表于: 2014-04-15
频响测试。
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只看该作者 74楼 发表于: 2014-04-15
upc1651频响不够平坦,无法照顾7MHz以下低端。
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只看该作者 75楼 发表于: 2014-04-15


输入输出电容使用了22PF,估计小了。
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只看该作者 76楼 发表于: 2014-04-15
隔直电容直接更换为100nF再看。


OK,低频延伸不错,1.6MHz在3db范围内。
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只看该作者 77楼 发表于: 2014-04-15
这曲线,带宽足够玩了。
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只看该作者 78楼 发表于: 2014-04-16
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只看该作者 79楼 发表于: 2014-04-16
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