[PCR-1000] Unsquelched Discriminator Output

[Erik Schorr]

Running the discriminator output through any sort of equalizer or analog
filter will introduce phase distortion into the signal, which will certainly
reduce the ability for any DSP algorithms to "lock on" to a digital signal.

For example, your graphic EQ has man parallel 2nd-order bandpass filters
spaced about one octave apart, or 3rd-order bandpass filters spaced at 2/3rd
octave intervals.  These types of bandpass filters have group delays that
vary depending on frequency of the sigal.  It might not be noticeable to the
human ear, but DSPs can't handle the phase distortion, especially when the
signal being processed is modulated in the frequency (FSK) or phase
(PSK/QPSK) domains.

- Erik Schorr < erik-qth @ arpa.org >

----- Original Message -----
From: "N5NAY" <n5nay@carolina.rr.com>
To: <pcr-1000@mailman.qth.net>
Sent: Friday, April 04, 2003 5:40 AM
Subject: [PCR-1000] Unsquelched Discriminator Output


> I am running the discriminator output thru a stereo graphic equalizer to
the
> line in of the sound card on the left channel.  The right channel is
> connected to the pcr1k regular audio output. If I don't want to monitor
the
> control channel, I mute the left side.  Has anyone tried monitoring the
900
> mhz systems?  I get a good strong signal, but not much over 40-50% on the
> decode.  I've also noticed that I have to restart the program to make it
> decode the datasteam every time I change control channels.  Otherwise, the
> program has worked flawlessly for me.  Thanks again to Jay for writing a
> well needed program.  This is one piece of software I will definitly
> support!
> I'm not real clear on whether the sound card is acting like a 2 or 4 level
> decoder. 4 level would be nice. I work in the paging industry,  &  need to
> monitor 4 level flex paging systems.  (Beats having to buy a 1500 Grayson
> decoder!)
> Dave