Path: utzoo!attcan!uunet!samsung!usc!apple!kchen
From: kchen@Apple.COM (Kok Chen)
Newsgroups: comp.dsp
Subject: Re: Hilbert Transformer
Message-ID: <42414@apple.Apple.COM>
Date: 27 Jun 90 16:13:24 GMT
References: <267ADD3E.18081@maccs.dcss.mcmaster.ca> <4834@uafhp.uark.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 28

cdc@uafhcx.uucp (C. D. Covington) writes:

>In article <267ADD3E.18081@maccs.dcss.mcmaster.ca>, darel@maccs.dcss.mcmaster.ca (Darel Mesher) writes:
>> 
>>   I was wondering if anyone has a reference to an analog implementation
>> of a Hilbert transformer (ie. 90 degree phase shift). I also need
>> a digital implementation but that should be fairly easy to find 
>> (Oppenheimer/Schafer).

>     I would say the analog version would be difficult to come by.  
                                              ^^^^^^^^^

Not quite. There is a simple (and, very insensitive to component 
tolerances) iterative method in the analog world for successively 
approximating quadrature shifts known as a Phase Sequence Filter.  
Unfortunately, the only references I have found on it are in 
Horowitz and Hill's "The Art of Electronics" and the ARRL (yeah, 
no kidding) "1990 Radio Amateur Handbook."  Both of which are a
little embarassing to use as citations (sorry, Paul)  :-) :-).

I, myself, would appreciate Email from anyone who knows a source 
with a better mathematical description of the Phase Sequence filter.  
My interest in that is whether an equally simple analogous (no pun 
intended) animal exists in the digital world.


Kok Chen, AA6TY				kchen@apple.com
Apple Computer, Inc.