[Discuss-gnuradio] Short pulses and ringing

[Marcus Leech]

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?