Sunday, January 18, 2009

Yesterday, Today, and Tomorrow

Yesterday I worked fairly hard on the wideband IQ imbalance mitigation problem. It is clear that the correct approach to this problem is to make the performance of the radio better and to ignore the primarily pyschological issue of the sensitive spectrum analyzer display.

The figure below shows the IQ correction for receive strictly limited to the passband of our receiver for the 7 MHz amateur band.

The next figures shows the necessary correction to IQ balance the entire IF passband at one frequency, 7.150 MHz in the Flex 5000. This will be a truly painstaking set of data collection to try and fix the entire wideband problem so the spectral display looks nice when what we should care about is improving the performance of the radio in the passband of the receiver. To do that across the entire 40m band (for example) can be trivially done from the data in the first figure.

The data collection and the new training algorithm will be installed in the PowerSDR code base before I leave. We then take the slower approach to mitigate the perceived wideband problem, which has NO impact on receiver performance but impacts the display. The wideband IQ correction will not easily lower the image to the noise floor across all frequencies. It can and should lower it to near the noise floor and to a greater extent than we currently do.

Yesterday I read most of Neal Stephensen's Snow Crash. He takes a road that combines the troublesome aspects of technology aptly shown in Gibson's Neuromancer and the biting social commentary of Pynchon's Vineland . I am very sorry I have not read him before now. Most place him in cyberpunk. This is not an adequate label.

Tomorrow Eric Wachsmann and begin adding the new IQ algorithms into production, including addressing all of the ugly issues that comes with supporting a large user base.

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