I need an FSK decoder

[Steve Miller]

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
find a device that will convert frequency to voltage, continuously,
over the same range.

I could sure use some help. Thanks, Steve Miller WA4LDA
ihnp4!bellcore!bambi!steve

[a...@nonvon.uucp]

I suggest you contact EXAR. They manufacture several IC's that
are usefull building blocks in such circuits. i.e. FSK modulators,
decoders, modem filters.... If you're around the 408 area code, I
think their distributors are "Bell Industries" @408 734 8570. Also
another company... Silicon Systems makes some parts in like this.
Of course, you could always get a standard PLL and start from there.
BTW, the EXAR people have several data books that have tons of MODEM
and PLL circuits.

Hope this helps...

-apn

uucp: ihnp4!ptsfa!nonvon!apn

[Larry Lippman]

In article <5...@bambi.UUCP>, st...@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
==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry
==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo|utzoo}!/
==> FAX: 716/741-9635 {G1,G2,G3} "Have you hugged your cat today?"