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From: rjr@mgweed.UUCP (Bob Roehrig)
Newsgroups: net.ham-radio
Subject: Using PLL IC's for RTTY demodulators
Message-ID: <14915@mgweed.UUCP>
Date: Fri, 18-Jan-85 16:16:47 EST
Article-I.D.: mgweed.14915
Posted: Fri Jan 18 16:16:47 1985
Date-Received: Sat, 19-Jan-85 04:28:32 EST
Organization: AT&T Consumer Products - Montgomery Illinois
Lines: 15


The problem with 567's as TU decoders is that with proper lowpass filtering,
they do not respond fast enough. Rather than use tone decoder IC's like the
567, you should use either a 565 with a slicer after it (a sample circuit
is in the Signetics data book), or better yet, one of the PLL chips that is
designed for that purpose like the Exar XR-210.

In any case, a PLL demod is lousy on the HF bands without channel filtering
ahead of it, or it will lock onto the strongest signal within its capture
range. They should be preceeded by either toroidal or active filters tuned to
mark and space tone frequencies. Also, the VCO in the device should be tuned
(with no signal input) to midway between mark and space.

Bob K9EUI