[TriLUG] Television & RF interference -- yes computer related -- I think

James Jones jc.jones at tuftux.com
Thu Mar 7 10:04:51 EST 2013


Joe,

The main idea of the drawing was to show location and connections of
the displays (monitors) since you had mentioned that my wording about
monitors was confusing.

And I did want to "show off" my block diagramming skills. :-)

Thanks for all your comments. I believe that I have more questions for
the producer & possible the preacher. I don't think I have the
complete story. Especially the part about -- "has anything changed
recently?"

jcj

On Thu, Mar 7, 2013 at 9:53 AM, Joseph Mack NA3T <jmack at wm7d.net> wrote:
> On Thu, 7 Mar 2013, James Jones wrote:
>
>> After finally getting around to transferring my notes to a block drawing (
>> see attached pdf ),
>
>
> these are stripped by the mailing list. But I'm not going to be able to
> pinpoint it from the diagram anyhow.
>
>
>> Your thoughts on this are appreciated. As a side note, their cabling is
>> more of a rat's nest and it looks like I get to help them organize it.
>
>
> Other people have had good suggestions, eg making sure the power cabling is
> earthed and wireless mikes (which you've eliminated). The lesson from them
> is not so much what to look for, but how to think about it.
>
> At the outset you have to face
>
> o you may not solve it, one of the problems being that you can't make the
> problem occur on demand. There is nothing harder to fix than an
> intermittant. You will have to accept bad recordings in the short term and
> maybe long term. To know when it happens, you'll need the recording device
> running 24*7, which presumably will require a human on hand.
>
> o it may take a long time. Before you start, decide how much time are you
> prepared to put into it. When that time comes, will you really quit, or will
> you just keep going?
>
> If you do fix it, the explanation will almost certainly be obvious after the
> fact, but it's unlikely that you'll be able to find it by rational means. In
> that case you'll have to take the monkey-typewriter-sonnet approach.
>
> Finding the problem here is no different, thinking wise, than fixing a
> software bug that only appears intermittantly.
>
> You'll have to find out what all the cables are doing and simplify it as
> much as possible (are all the cables shielded? - I don't know what you have
> - are the twisted pairs individually shielded? it the bundle shielded? is
> the shield earthed at each end? - this itself will be a nightmare.). Make a
> plan for what to do when the next RFI event happens and be prepared to start
> disconnecting cables. Have some idea of how you'll interpret what is going
> on if the RFI remains/stops.
>
> You need to get to the simplest setup that reproduces the problem and have a
> list of what stops it. Can you take out the video switcher and record
> directly from the camera? (You may need to borrow gear from a different
> manufacturer, but with similar specs, to substitute to see if anything
> different happens.) You may wind up in the unhappy situation that
> eliminating RFI means you can't record.
>
>
> Joe
>
> --
> Joseph Mack NA3T EME(B,D), FM05lw North Carolina
> jmack (at) wm7d (dot) net - azimuthal equidistant map
> generator at http://www.wm7d.net/azproj.shtml
> Homepage http://www.austintek.com/ It's GNU/Linux!
> --
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-- 
Jc Jones
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