ORIGINAL: captinjohn
ORIGINAL: coronabob
Super fast discharge/spark generates harmonics and ringing in a non-resistor plug. The resistance softens the discharge (slower di/dt) and thus no radio interference to speak of. Metal to metal rubbing is the culprit, not the ignition itself.
Some time ago I spent half a day looking for radio interference sources. I used an oscillator to trigger the CDI in lieu of a hall sensor on our engine. I had the spark plug laying on the bench sparking away. With the 'antenna' near enough to almost touch the spark itself or anywhere near the CDI board, I saw zero, nil, nata, nothing that would register on my digital phosphor scope. The 'receiver' was a germanium diode/LC tank. However, when I rubbed/scratched a screwdriver tip on something metal nearby I would pick up beaucoup noise even feet away from the antenna.
I mentioned the copper paint just because someone asked. In other words, I do not believe shielding any box will buy anyone anything in our gassers. Getting rid of metal rubbing contacts and minimize engine shakes will eliminate our woes.
Does this mean we have to install ceramic bearings and teflon coat the piston? Capt,n
There are two type of EMI/RFI
1) Radiated.
2) Induced.
The shielded spark plug connectors (with resistor) will take care of the radiated EMI/RFI.
The secondary source, induced. Will be up to us to eliminated, employing any known mean (CF or plastic pushrods, plastic servo arms, plastic clevis, opto couplers, enough distance, etc) this induction is created by any conductor or set of conductors, wires, screws, engine mounts, batteries, creating "circuits" or loops, etc. Once these loops are created, all it takes is to open these loops to generate those feared RFI/EMI noise in our airplanes .
If the proper conditions are met, then this induced noise will become another source of type 2.
Our intricate set of wires inside the fuselage, connectors, batteries, etc, will be a good path for any induced EMI/RFI.
Will this noise be amplified, maybe? Will be attenuated maybe. It all depends on the how good we are to enhance them or reduce them. If one of these loops finds its way through a clevis and a metallic servo arm (for example). Then we are calling for a metal to metal friction: the loops will intermittenlty be opened, therefore they may very well trigger RFI/EMI events.
Now, a large mass of metal such a cylinder, crankcase and ball bearings moving like crazy, will easily adsorb any additional electric charge. If we can put it in one word the large mass represented by the engine acts like the actual “ground”. Will be the zero potential if you want.
So don’t worry about this friction.
You don’t have to think about ceramic bearings and so.
It is metal to metal friction, however is large enough with a lot of free electrons that will draw any current generated by 1 or 2 above.