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[Discuss-gnuradio] Short pulses and ringing

From: Marcus Leech
Subject: [Discuss-gnuradio] Short pulses and ringing
Date: Thu, 09 Mar 2006 08:45:11 -0500
User-agent: Thunderbird 1.5 (X11/20051201)

Many of you know that I'm experimenting with pulsar detection and monitoring tools for
 Gnu Radio, as part of a larger radio-astronomy toolkit for Gnu Radio.

Pulsars produce narrow pulses with quite fast rise times, with pulse repetition rates of less than 1Hz up to tens or hundreds of Hz. The pulses tend to have fairly-fast rise times.

My pulsar profile monitor uses the audio system to monitor the detector output of a USRP-based RF front end. That front-end does broad spectral analysis, and also produces an 8Khz sampled audio signal for use by the pulsar profile monitor, which uses epoch folding.

In order to test the pulsar profile monitor, I have a small program that produces short pulses, buried in random noise (just like you'd find with a real pulsar). What I'm finding is that the displayed pulse profiles bear very little resemblance to the generated profile, with ringing and undershoot. What I need to understand is whether it's the audio subsystem that's ringing, or the FIR filter that I use in the pulsar
 profile monitor.

How to FIR filters react to fast-rise-time pulses? Do they ring like analog filters?

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