Re: [ultra-cheap-sdr] Digest for ultra-cheap-sdr@googlegroups.com - 1 update in 1 topic

[David Lundberg]

Yet another great discovery and demo!

// David

Den 2 feb 2015 08:09 skrev <ultra-c...@googlegroups.com>:

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• R820T - 1 Update

R820T

Leif Asbrink <le...@sm5bsz.com>: Feb 02 03:46AM +0100 Hi All,   The rtl-sdr library from Osmocom uses R820T with an IF filter bandwidth of 5 MHz. This means that the peak amplitude of all the signals within this bandwidth has to be below the point of saturation for tha ADC.   To accomplish that on a crowded FM band it is necessary to turn down the gain which means that weak stations can not be heard because of the degraded NF.   It is possible to do much better. The IF filter which actually is a low pass filter and a high pass filter can be set for a bandwidth of 300 kHz. Dynamic range increases by something like 30 dB for the second next channel 400 kHz away. It is also possible to get some more improvement by changing the gain distribution.   Sampling should remain at 2.4 MHz because the stop band attenuation is not very high and if sampling at 300 kHz one would get aliases from signals outside the filter if they are strong.   Here is a video showing the difference between the Osmocom library and a modified library: https://www.youtube.com/watch?v=btDiWHuI730   Amusing that the cheap dongle has lower phase noise than the low noise synthetized generator from Hewlet Packard. An oldfashioned vacuumtube generator is needed to find the performance of the dongle...   The modified library can be obtained like this: git clone https://github.com/dl8aau/librtlsdr   A dll for Windows is available here: https://drive.google.com/file/d/0B9m6SAaGpewQeWtyS0lzdW1xVmM/view?usp=sharing   Linrad-04.04 will soon become available here: http://www.sm5bsz.com/linuxdsp/linrad.htm   Regards   Leif

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