Postby Matt Harrowven » April 29th, 2010, 9:11 pm
Shamelesly lifted from a quote on RCMF from Dr Keith Mitchells Radio Installation booklet
HTH
You will need around 7-8 metres of TV co-axial aerial, as binding the lead takes a surprising amount of material. Strip-off the outer plastic sheath and slide off the copper, braided screen - which is the part which is to form the screen. Flatten this length of braid and at its centre form a loop in it at right angles to its length. This loop should be long enough to extend from the base of the H.T. lead where it exits the magneto block, to a convenient screw point on a main conductive part of the motor e.g. crankcase, fin or engine mount. From the exit point on the magneto block one half of the copper screening lead is wound in a clockwise direction up the H.T. lead. After the first turn secure it to the lead with a small cable tie or strip of electrical tape; this will help keep the whole assembly in place as you progress. Try to keep the turns together minimising air gaps - the job, I’ll admit, is fiddly, but keep patience. It gets particularly difficult at the plug cap but this has to be covered and this is where you will notice your seemingly generous length of braid being ‘gobbled up’ at an alarming rate. Once at the end of the cap, trim and secure with a turn or so of electrical tape. Now to the other half; this needs to be wound up in an anti-clockwise direction over the top of the first half, again ensuring that all air gaps are filled (NB air gaps in electrical shielding are like holes in water pipes, EMI searches ‘em out). Once at the cap end, trim and then bind the whole lot with electrical tape all the way down to the magneto. Don’t despair if it doesn’t look particularly neat - it’s effectiveness that’s important here and what you have tried to achieve is a conformal copper sheath which will reduce radiated EMI which comes not only from the lead but the unshielded ceramic of the plug itself. Complete the job by earthing the ‘loop’ on the motor body.
Matt 3066
LMA No. 3066
