What is this for?

'Sounds more like a static thing to me.

 

the AM radio was old school Diagnostics for tunup time...LOL

 

Listening to AM radio, don't you mean ..."Sounds like a tiny bit less static to me"? .... it almost hurts to listen to AM after all these years, after listening to relatively clean FM signals.

I had HD FM radio in my last daily driver, and was assured that the new one had it too, by a salesman who almost new his facts, because the car has "the large touch screen". It doesn't, and now jumping backwards into regular FM has the same effect. Feels like a scheme to sell satellite radio.

 

I was referring to static electrical build-up on the surface of the hood, and perhaps a slight reduction in RFI from the ignition system by some sort of Faraday Cage shielding (would only be slight).

I don't listen to any FM radio anymore, and haven't in years. There's no good music on there, and with CDs and mp3s (and now XM satelite radio), there's no more reason to. I listen to AM for news and talk. I would never want to listen to music on AM.

 

OMG! Sometimes you just have to pick up a book, and start reading.

Let's consider an ignition system (both the primary side and secondary side), alternator and relay circuit, starter relay and starter, instrument voltage regulator circuit, and rotating tires that can generate static electricity, etc. that combined, is a random noise generator emitting a Gaussian curve of E and H fields - all underneath the hood. Understand where I'm going with this???
The hood (made of metal) has a finite dimension in space that, electrically, can be represented as a product of Resistance + Capacitance + Inductance = Z (Impedance).
If the hood isn't perfectly grounded (the vector addition of current nodes = Zero) across the whole hood; it is capable of containing a voltage potential that is constantly increasing in potential & haphazardly decreasing in potential through discharge through whatever grounding is available (hinges latch), and whose resistance in constantly changing. Since the discharge paths are not perfect due to mechanical fluctuations caused by body & chassis movements - that in and of itself has the potential to generate signals in the Radio Band. Since they are changes in amplitude and repetition rate (frequency), they are easily picked up by a standard broadcast receiver in the 530 - 1700 KHz range AM.

In addition, road salts, and other chemicals can electrically act as semi-conductors along electrical paths that can generate "intermodulation". Intermodulation interference is the undesired combining of several signals in/through a nonlinear device or substance, producing new, unwanted frequencies. Visualize an electrical path through a hood hinge that has road-salts, and other contamination in the axles.....

At work, part of the tests that I perform include radio frequency (RF) testing of components, circuit boards, and systems inside large anechoic and reverb chambers. Also, perform tri-axial single degree of freedom sine, random, and mixed mode vibration testing to greater than 40 g's - using dynamic shakers.

Yup! The best idea in these posts is the one suggesting a braided cable ground; screwed into the hood and chassis. And, yes, there is nothing in a trunk that is generating energy.

 

"braided cable ground"...brings up another question, will start another thread.

http://mmb.maverick.to/threads/braided-grounding-strap.106469/

 

"Braided cable" is very flexible. Solder or crimp "lugs" on the ends, and you'll be just fine - for the frequencies that we are are considering, "braided cables" are fine. We are not talking about UHF & microwave frequencies vs. "skin effect".
Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. For greater than 1 MHz:

Table below gives approximate values of “k” factor for various round wire sizes.

 

what was the question again...LOL