[Healeys] Distributor screen

[Alex]

The knot forms a crude coil, which exhibits inductance, and therefore some inductive reactance at the AM frequency. A coil is sometimes referred to as a choke. This knot technique is very, very crude. It would be better to wind some turns around a ferrite core, if a choke is what you want for noise suppression.

== Alex in Maine
     "The Blue Mainie," 1960 Austin Healey 3000 BT7
     "Conkling," 1946 M.G. TC #1321
     Former owner 1957 A-H 100-6, 1967 A-H BJ8, 
     1965 MG Midget   ‹(•¿•)›
     http://ai2q.org/


  ----- Original Message ----- 
  From: Michael Oritt 
  To: Wilko2 
  Cc: Austin Healey 
  Sent: Wednesday, December 02, 2015 8:50 PM
  Subject: Re: [Healeys] Distributor screen


  This reminds me of something I witnessed many years ago when I had a TR3 with an AM radio which was picking up a lot of ignition noise--actually a very loud tick that varied directly with the engine's speed.  A mechanic showed me that simply tying an overhand knot in the lead (no doubt a solid copper wire) from the coil to the distributor eliminated the noise. 


  I have told this story to several people over the years and have always gotten skeptical responses but I will go to my grave insisting that it happened.  I have searched the internet for any reference to this phenomenon and the closest I can come is here:


  http://physics.stackexchange.com/questions/13978/tying-knots-in-power-cables-to-prevent-power-surge-from-lightning-strikes



  Perhaps an electrical smart guy can shed some light on why the knot works but that is my story....


  Best--Michael Oritt


  On Wed, Dec 2, 2015 at 7:40 PM, Wilko2 <e-wilkins at cox.net> wrote:

    The "screen is certainly an electronic suppression device. In the parts lists it's called a "Suppression screen - France only" Probably works a bit like a "Faraday cage" 





    From BMC document AKD 3513:





    On Dec 2, 2015, at 2:56 PM, Peter Svilans wrote:


      I'm with Steve on this.

      The operative word here is "screen", which generally means keeping out rocks and dirt.

      But these (two types of) sheet metal "screens" fitted to the French market Healeys are on the Ignition Cables page (MB2) in the Parts List, along with "screened" ignition leads which look quite different than the "suppressed" leads on the same page. France got the screened equipment, Norway, Hong Kong, Denmark and Germany got the suppressed leads, and we got the plain ones.

      Peter
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