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LF: Bugfix for ebnaut_ifft utility

To: [email protected]
Subject: LF: Bugfix for ebnaut_ifft utility
From: Markus Vester <[email protected]>
Date: Wed, 7 Jun 2017 11:59:04 -0400
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In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]

Dear EbNauteers,

I recently stumbled upon a bug in my ebnaut_ifft3a utility, which is used to convert SpecLab FFT export files to IQ wav files. The first step of the inverse FFT is to take the complex conjugate of the data array. Due to the bug, the respective loop was executed only N-1 times, leaving a sign error in the imaginary part of a single bin next to the center frequency. When fed with a high-SNR signal close to SpecLab's center frequency, this can produce strange undulation patterns in the phase display and a minor SNR degradation for the decoder.

The bug has been fixed in version 3b, available on
 http://df6nm.bplaced.net/VLF/fec_tests/ebnaut_ifft3b.zip

Best regards,
Markus (DF6NM)

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