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From: bryce@hoser.berkeley.edu (Bryce Nesbitt)
Newsgroups: comp.sys.amiga
Subject: Re: Better video, in three easy steps.
Message-ID: <3822@zen.berkeley.edu>
Date: Fri, 18-Sep-87 22:59:37 EDT
Article-I.D.: zen.3822
Posted: Fri Sep 18 22:59:37 1987
Date-Received: Sun, 20-Sep-87 11:19:38 EDT
References: <3795@zen.berkeley.edu> <169NETOPRHM@NCSUVM>
Sender: news@zen.berkeley.edu
Reply-To: bryce@hoser.berkeley.edu.UUCP (Bryce Nesbitt)
Organization: Center Tapped Solids, Inc.
Lines: 37
Summary: Why it helps.  Would the "A2000 Guy" like to comment?

In article <169NETOPRHM@NCSUVM> NETOPRHM@NCSUVM.BITNET (Hal Meeks) writes:
>The big question is -- Why (and how) does it work?
>I would like some idea of what I am doing before I go munging
>around in the innards of my brand new beige box.

[read the referenced article to know what is going on]

Ferrite beads are commonly used on output signals to attenuate higher
frequency noise that might otherwise be radiated exte rnally to the
computer.  (Incurring the wrath of the Federal Crap-Cutters :-).

Why ferrite was used on the *VIDEO* output is beyond me.  I'll need to
assume that for the A2000 it has something to do with the German version of
the FCC, which has what I have heard are strict requirements. ( I don't
know about that rumor... US companies always use the FCC as a scapegoat for
late products.	I've never heard this excuse used for a German design...
so... )

In this case what the ferrite attenuates is part of the signal!  On the
A500 I have next to me it is (was) an in-line ferrite with one hole.  The
A2000 prototypes in town are the two hole, two loop type.  That *really*
does in a video signal.

Why, again, I don't know.  Even without the ferrite that connector is not
going to radiate... it's connected to a shielded cable.  My circa 1986 FCC
docket is not clear if one must test with and without cables attached.	If
so, the solution is simple: add a 15 cent stamped metal end cap.  An empty
connector would be covered, a full one would have a shielded cable.  Users
would be instructed to use the cap or a cable.

Mr. A2000 guy?

 
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