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From: bill@videovax.UUCP (William K. McFadden)
Newsgroups: net.video,net.analog
Subject: Re: MTS stereo decoder
Message-ID: <1543@videovax.UUCP>
Date: Tue, 11-Feb-86 13:10:51 EST
Article-I.D.: videovax.1543
Posted: Tue Feb 11 13:10:51 1986
Date-Received: Thu, 13-Feb-86 19:47:26 EST
References: <218@catnip.UUCP>
Reply-To: bill@videovax.UUCP (William K. McFadden)
Organization: Tektronix, Comm Group, TV R&D
Lines: 61
Xref: linus net.video:2015 net.analog:680

In article <218@catnip.UUCP> ben@catnip.UUCP (Bennett Broder) writes:
>The current (March 1986) issue of Radio-Electronics magazine contains
>plans for a stereo tv decoder.  I was pleased as punch to see this, since
>I have been looking for a cheap and convenient way of adding stereo decoding
>to my video system.  It looks like it could be built for about $40.
>
>Here is the rub.  The circuit does not contain any noise reduction.
>Apparently, the compression technique used is proprietary to dbx, and
>the chips necessary to do it are available only to licenced OEMs.
>So, my question:
>
>  - Is it worth building one of these?

NO! NO! NO!

>  - How noisy will it be without the dbx chips?

About as noisy as FM Stereo, when compared against FM mono (e.g., S/N is
degraded by 23dB on weak signals).

>  - Will there be any other unwanted side effects (breathing noises
>       or frequency response abberations) without the dbx?

YES!  Only the L-R channel is compressed.  If you try to rematrix it with
the L+R without first expanding it, the separation, at best, could be
described as terrible!  This is the primary problem with the R-E circuit.

>
>If I get enough responses and/or actually build one of these things,
>I will post a summary.
>
>Ben Broder
>{ihnp4, decvax} !hjuxa!catnip!ben

I too, was surprised when I saw "Build This Stereo TV Decoder" on the front
cover of _Radio-Electronics_.  My first thought was, "Gee, they finally came
out with a chip to do the dbx decoding?"  I quickly turned to the article
and, looking at the schematic, the first words out of my mouth were, 
"This won't work!"  I am tempted to write a letter to the editor of R-E,
telling them they shouldn't have jumped the gun.  

In my opinion, you would be better off buying a real MTS decoder and not
wasting your time building this circuit until the dbx chips are here.
Otherwise you will be dissappointed.

On the positive side, the article is educational.  It explains how the MTS
system works.

A few months ago I wrote an article on the workings of stereo television.
If anybody is interested, e-mail me and I will forward it.  Also, feel free
to ask me any questions you might have about MTS.  If I don't know the answer,
there are lots of other people around here who do.

                                    Bill McFadden
                                    TV Measurement Systems
                                    Tektronix, Inc.

-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-594  Beaverton, OR  97077
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GTE:  (503) 627-6920        "How can I prove I am not crazy to people who are?"