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Path: utzoo!mnetor!seismo!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.analog,net.ham-radio
Subject: Re: I need an FSK decoder
Message-ID: <1334@kitty.UUCP>
Date: Sat, 11-Oct-86 23:22:27 EDT
Article-I.D.: kitty.1334
Posted: Sat Oct 11 23:22:27 1986
Date-Received: Sun, 12-Oct-86 03:25:56 EDT
References: <550@bambi.UUCP>
Distribution: net
Organization: Recognition Research Corp., Clarence, NY
Lines: 35
Summary: Two possible techniques...
Xref: mnetor net.analog:872 net.ham-radio:2362

In article <550@bambi.UUCP>, steve@bambi.UUCP (Steve Miller) writes:
> I'm looking for a device that will perform Frequency Shift Keying
> decoding, with input frequencies of 1500 Hz (mark) and 2300 Hz (space),
> at a faily rapid rate (300 baud or better).  Also, I would like to

	Since those frequencies are neither Bell nor CCITT V.2X, I can't
direct you to an integrated modem chip.  The frequencies sound like
radioteletype with an 800 Hz shift - but I don't know of any integrated
FSK converter chips for that application.
	So, you can take two approaches:

1.	Use an phase-locked loop, either a LM565 or LM567.  Check National
	Semiconductor Application Note AN-46 for design details and
	examples.

2.	Use a switched-capacitor filter in a narrow bandpass configuration
	for each frequency, with a simple op amp AC level detector at the
	filter output.  This is a more state-of-the-art method; while more
	complex in design than a PLL, these filter-based FSK detectors are
	far superior to a PLL.  Consider the National Semiconductor MF-10 as
	a starting point, and get a copy of the National "Switched-Capacitor
	Filter Handbook" for design details.

> Also, I would like to
> find a device that will convert frequency to voltage, continuously,
> over the same range.

	Consider the National Semiconductor LM2907, which is a building
	block circuit providing F/V conversion for tachometer and other
	applications.

==>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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