So does my theory B apply to inductors that the EM field created collapses when the current draw increases and is converted back to current? My MECP doesn't make me an electrical engineer, but it did increase my curiosity.

 

What happens is that when current first begins to flow, the magnetic field that results from it is also building - which requires energy from guess where? The current itself. That current (or power) is being absorbed to create the magnetic "FLUX" field. Every wire or conductor that has a current flowing through it also forms a magnetic field around itself to some degree. It can be said to have a parasitic effect on the current until the field and the current flow equalise.

When you have a coil, the coil windings reinforce the effect, which is greater, so it takes more energy. Two or more wires next to eachother with the same current going through them have a bigger combined magnetic flux field than if they were seperated. That is an example of magnetic field "Coupling". The better the field coupling, the greater the field.

Irregardless - because of all this, we say that inductance opposes the flow of current.

Inductance is the action of a magnetic field resulting from current flowing in a conductor. It resists current flow until the field is fully built up, which is the opposite of a capacitor.

When the current stops flowing, the energy stored in the field returns to the conductor as the field collapses. (!)
Go figure - at least in part that's how your ignition coil works....

Another interesting property of inductors is that a coil can pass DC current, something a capacitor can't do. But a capacitor can couple an AC current across itself. Inductors also can pass AC, but they affect the rise and fall times of the voltage. Both can be thought of as storage devices for electrical charges - but in different ways.

Even more intriguing is transformer theory - where two inductors (coils) share space, and the field in one inductor causes current flow in the other even though they are insulated and seperate from eachother electrically and mechanically.

I was taught the 3-I paradigm: Transformers provide current (I) changes, Impedence matching, and Isolation from one circuit to another.

That isolation mainly applies to DC though. It's kind of obvious that signals can be carried across a transformer even when you don't want them to be.


(Just nod your head and say: "I gotcha, Perfesser Wolfie, yep - sure do...")


ALL OF THAT just to say this:
When you loop your antenna wire, you are forming a coil - even if it IS shielded.

That ain't good.

 

But once the field is charged they resist change in current and not just the flow of current?

We only covered inductors in so much as using them for low pass cross overs.

I can understand what your saying about building the field and it dissipating back into the windings as current. However, the CoAX is shielded so that should change the properties of the windings, correct? In my mind that change in the winding's property is to reduce the field coupling. So while it may not eliminate the field, it shouldn't amplify it beyond how it would normally build a charge?

 

OBSERVE Grasshopper:

When the current is taken away, the EM field collapses. While the current is maintained and only then - the EM field exists as a property of current flow. The collapse of the field serves to provide an instant of additional current as what created it is removed.

Useful to know when dealing with AC voltage or RF....

Also keep in mind that the braid itself will pick up signal, even though it is shunted to ground.

And yes - it resists changes in current flow - EXACTLY!

 

As amperage increases so does the field (strength/size), as it decreases, the EM returns to the conductors as current. got it.

Now the EM field in the coax is the same as as radiating from the antenna? Because there is a 50ohm load at the antenna end leads me to believe that there is a significant change in either voltage or current, E=IR should still apply right? So does the wave length change in the conductor?

So how much shielding would it take to completely isolate the RF in the coax?

 

You can't completely isolate it, that's my point.

Your power is only during transmission.

For tuner sensitivety, normal shielding should be alright. Just make sure you have good grounding between the engine (alternator), frame, and body structure.

And don't loop your cables - even if you have to run them a mile to keep them away from eachother.

Also keep in mind that the cable length has to match the wavelength - just like the antenna does.

If you have a load at the antenna - I'd get rid of it. Nothing beats a stainless steel Wilson.

 

Everything you want to know is RIGHT HERE:

www.wilsonantennas.com

 

I thought the antenna was a 50ohm load which is why you have to have a 50ohm dummy for testing without an antenna. Also why this formula uses 50ohm in ohms law for power calculations. A.H. Systems - RF Related Conversions

 

It may be so - but the best antennas are direct extensions of the cable

 

I'll try not to write a book here, but as a general class ham, and a powerstroke owner here is what I would do. First, I would unplug the coax from the radio and listen for the noise. If it's still there, go to radio shack and get two of these. One for the positive lead, one for the negative.

RadioShack.com - Cables, Parts & Connectors: Component parts: Inductive products: Snap Choke Core

Also make sure your leads aren't running parallel to other wiring. If the noise stops with the antenna unplugged, you may need to look into moving the antenna because right now it's mounted right over the fuel injector amplifier box which is noisy. And if you think your fuel pump could be your noise source, make sure it has a good clean ground connection to the frame. Hope that helps you out, good luck with it.

 

Does the noise go up and down with engine RPM?

Or is it just plain static?

 

Wow! Lots of good info has been posted! Thanks guys!

If I unplug the coax from my CB --- noise gone

If I remove the antenna from the mount -- noise gone

So it seems that my antenna really is picking up this noise from somewhere...?

The noise does not increase as the engine speed increases so I guess that rules out the ignition system?

Thanks again guys! Rep points sent

 

It rules out both the alternator AND the ignition system. Of course, it could be computer noise. Does it have any kind of tone or frequency to it, or again, is it just white noise/static?

 

It does have somewhat of a higher pitched tone than just plain old static.

 

Actually just re-read what you posted, when I asked if the noise go up and down with the engine speed, I meant frequency-wise, not volume-wise.

Anyway, what you have seems to be electronic interference, if it's somewhat of a tone, something in the truck is generating that tone. Could be the PCM or another electronic gizmo. Got any anti-theft stuff that's not stock? Cell phone charger plugged in all the time?

Better yet, is the noise there when the ending is NOT running (and the ignition key is NOT in the ON position) ???

The ferrite cores that jwrench posted could help alot. I'd check into a more sophisticated noise filter hooked inline with the power supply to the CB, like the ones used for car stereos (if they can handle enough amperage for transmitting). They are basically a simple filter, an inductor inline in the +12V, with a capacitor from the output of the inductor to ground.