The decimation filters of the SRM SDR radio receiver

Quadrus SDR | Multi-channel SDR software receiver decimation filter response
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Multi-channel SDR digital receivers

As you may know, the DRU-244A digitizer card contains multi-channel SDR multiple AD6624A Digital Down Converter (DDC) chips, which select narrower channels from the incoming 40 MHz Nyquist bandwidth signal. The DDC filters may be designed using the Softcell software package that is provided by Analog Devices and can be downloaded from their web site, but available from our site too. The designed filter itself is stored in a *.F24 file that includes the coefficients and some miscellaneous parameters as well. The filter is downloaded into the digitizer hardware by the driver, and thus can be later updated via an API call of the card. You can use a simple dialog control to select the decimation filter in the test software. Please note that the DRU card and its driver support only one filter for all (up to 16) of the DDC channels.

Supported decimation filters in SRM multi-channel SDR software receiver

There are five built-in decimation filters in the SRM-3000 multi-channel SDR software receiver. The filters themselves are hard-coded and handled by the DRU device driver. They are stored in the DRU244A.bin file in the windows directory. The filters are downloaded by the drivers, and can not be changed on-the-fly. You have to stop the sampling, select the new bandwidth on the options panel, and restart the acquisition again. The filters have higher bandwidth and are running at higher sampling rates than the bandwidth displayed in the multi-channel SDR software receiver. The display contains only the inner 1 dB band of the signals. This way they can provide flat response in the passband and up 80 dB suppression for the out-of-band signals.

The supported complex sample rates are: 24, 48, 96, 192, 384 and 786KHz. Complex signal means that for booth the I and Q channels we have this sampling frequency. This way the the available Nyquist bandwidth is the same as the sampling frequency of the complex signal.

The response of the above discussed five filters are very similar and looks like this:Quadrus SDR | Multi-channel SDR software receiver filter response

The associated *.F24 filter design files are available for download too. Decimation filters (*.F24) files The filter design software for open these file can be downloaded as well. Analog Devices Softcell Filter Design setup Please register with your email address to this BLOG for access the content for download.


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9 thoughts on “The decimation filters of the SRM SDR radio receiver”

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