ORIGINAL: All Day Dan
Randy, you’re doing the right thing by trying to figure this out while being bombarded by all of this excess rhetoric. My father spent a fortune paying to make me an electrical engineer. Unfortunately, I have forgotten more than I had learned. But here goes.
Your engine generates a spark around 100 times a second. Each one of those has the potential of containing radio frequency components that fall within the band that your radio is operating in. They radiate around the ignition system as an electromagnetic field and are conducted within all its wires going to and from its batteries and spark plug. By bringing the receiver and ignition components close together you violate all the advice from the radio manufacturer to isolate the radio components from the ignition system by eight to 12 inches or as much as possible. It is possible to pick up this RF through conduction and radiation. A lot of the guys ignore that by doing what is convenient or less expensive and get away with it. This gives them a sense of security that is very false. This is good because I hate to see guys go in but all you need is a few seconds of sparks that are on your frequency and you will lose control.
Its too bad your dad had to spend all that money. I got my education paid for by my uncle - uncle Sam that is.
But you don't need an engineering education to separate ignition wires from receiver wires. Common sense should tell you that.
That said your reference to the spark is off base I think.
The spark shorts the inductive pulse from the coil and makes it a square wave.
A square wave is defined as containing an infinite number of odd harmonics. But in our case its a finite number of odd harmonics. the lowest frequency contained is the fundamental of the square wave while the highest frequency is determined by the rise time of the square wave. We can control the rise time by adding resistance to the spark lead. That's why we can use an unshielded spark lead and not have it interfere with our receiver. But with 2.4 we don't even need that because the resistance of the line is enough to stop interference of the radio.