Hey, thats an excellent application for an otherwise useless item, a hot
knife for cutting foam.
Good one!
Carl
KM1H
----- Original Message -----
From: "Dave Harmon" <k6xyz@sbcglobal.net>
To: <amps@contesting.com>
Sent: Wednesday, September 30, 2009 1:45 AM
Subject: Re: [Amps] Parasitics can kill
> Hey....I got the fix right here.
> I'll send em' one of AG6K's parasitic kits that I didn't use!
> Mebby it'll work on a train......
> Oh...dang...wait....I forgot...I used the nichrome wire to cut foam
> wings....sorry.
>
> Regards
>
> Dave Harmon
> K6XYZ[at]sbcglobal[dot]net
> Sperry, Ok.
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of mikea
> Sent: Tuesday, September 29, 2009 9:14 PM
> To: amps@contesting.com
> Subject: [Amps] Parasitics can kill
>
> It's not just RF power amps that have parasitics, and sometimes they can
> cause people to die. The Association for Computing Machinery's newsgroup
> on the risks associated with computing and electronics published this
> fascinating article today:
>
> : Date: Tue, 22 Sep 2009 23:36:06 -0400 (EDT)
> : From: "David Lesher" <wb8foz@panix.com>
> : Subject: More on the DC Metro collision 22 June 2009 (RISKS-25.73)
> :
> : The NTSB has issued an urgent interim recommendation re: the fatal Metro
> : collision in June.
> :
> : <http://www.ntsb.gov/recs/letters/2009/R09_15_16.pdf>
> :
> : The letter discusses the failure they found:
> :
> : "Testing found that a spurious high-frequency modulated signal was being
> : created by parasitic oscillation from the power output transistors in
> : the track circuit module transmitter. This spurious signal propagated
> : through the power transistor heat sink, through the metal rack
> : structure, and through a shared power source into the associated module
> : receiver, thus establishing an unintended signal path. The spurious
> : signal mimicked a valid track circuit signal. The peak amplitude of the
> : spurious signal appeared at the correct time interval and was large
> : enough to be sensed by the module receiver as a valid track circuit
> : signal, which energized the track relay. This combination -- of an
> : alternate signal path between track circuit modules and a spurious
> : signal capable of exploiting that path -- bypassed the rails, and the
> : ability of the track circuit to detect the train was lost."
> :
> : and makes recommendations for WMATA, and other involved parties.
> :
> : Comment: Attention has long focused on the track signaling circuit that
> : inexplicably failed to detect the stopped train. What was not know was
> : why it failed; when AC track signals have been in use for a century.
> : After a great deal of work on the scene and off, NTSB has part of the
> : answer.
> :
> : The RISK here is this was and is the classic "all the eggs in one
> : basket" protection scheme. It was a very sturdy basket, but...
> :
> : Now the issue is how to retrofit real redundancy into this system...and
> : how to pay for it.
> :
> : [Doug Hosking noted a CNN item. PGN]
> :
> http://www.cnn.com/2009/US/09/22/transit.rail.alert/index.html?iref=mpstoryv
> iew
>
> --
> Mike Andrews, W5EGO
> mikea@mikea.ath.cx
> Tired old sysadmin
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>
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