"Grounded" Electricity

megashawn

I've installed alot myself. Consider this.

The antenna body is metal, more times then not. It threads into the car, also metal. The car, being grounded itself grounds the antenna. The outside metal of the antenna is connected to the part of the antenna which is grounded to the car.

You don't even have to plug the antenna in to ground the stereo. Touch the ground wire of the stereo to the outside of the antenna, or the outside to the chassis of the stereo.

This comes in handy especially in newer cars where everything is plastic and it is hard to find a good ground point.

chroot

Hmm I wasn't aware the antenna itself was grounded to the chassis.

- Warren

megashawn

Well, it is a little known trick, because 9 times out of 10 you already have the power and ground wires hooked up before you plug the antenna in.

Cliff_J

Most newer cars supply ground for the deck right in the harness. Pretty easy unless you really want to 'old school' the thing. On too many cars though, the antenna ground is near the brake light ground or what not, its just like asking for alternator whine or pops in the system if you have a lot of components.

Cliff

rayjohn01

to Megashawn
if the antenna is literally connected to the chassis ( assuming it's also metal -- then where does the radio input get connected ( it's antenna input).

Metallicbeing

According to the National Electrical Code, A ground shall be bonded at the electrical source (along with the grounding rod, neutral, gas and water pipes, metal structure, and foundation rebar) and maintain continuity throughout the metal parts of the entire electrical system. The NEC also states that a grounding rod shall not be the sole means of grounding.
What this means is that the grounding system is meant to be an emergency path back to the source if something "hot" were to make contact with exposed metal parts and surfaces. If you only use a grounding rod with the minimum requirements (25 ohms), it would not have sufficient continuity to trip the circuit breaker. The grounding rod is mainly a path for lightning.
Unfortunately, grounding systems that are incorrectly installed can be very dangerous. Some examples are bonding neutrals to the grounding buss in breaker panels, poor continuity throughout the grounding system, No bonding at the source (a floating ground), etc...
Electrically speaking "ground" means reference to 0 volts (ideal).

PMASwork

Yeah - I can empirically back that up!

Here in AZ, it can get very dry. I have stepped out of the car and received quite an uncomfortable shock.. plus, sometimes you accidentally brush the car with your calf or other body parts while exiting, so this nasty shock can get you in some very sensitive areas!

megashawn

This is true, however I am ole school and don't own a vehicle younger then 20 years old. Alot of times just using the metal straping that helps hold the stereo in place will ground it as well.

But hey, I'd had a car stereo hooked up in my bedroom before, trust me, there are millions of different configurations to hook it up. I used a pc power supply for that trick, worked like a charm.

About the alternator noise, I've never had much trouble with it. Infact, I started only using the antenna to ground because I've found I get more noise from using factory grounds then I do making my own.

Anyhow, sorry for the thread hijack :)

wimms

That is true. And anybody arguing this can only beg to differ in definition of crap.

megashawn

before I go through the trouble of taking a photo of such a setup in action, will it even do any good?

I hate when people are so blinded by there "education" and "expieriance" that can't take a second to realize that maybe, just maybe there is another way of doing things.

Integral

All the car antennas I have dealt with are coaxial, there is an outer shield, which is ground, and an inner conductor, which I have always assumed is different from ground. Are you using the inner conductor as ground, or the Shield?

megashawn

You plug the antenna in, the stereo is grounded. I may have explained it incorrectly earlier, but I assure you, it works. I will post a pic of a system working if need be.

I would imagine it is the shield wire, as it is in contact with the outer portion of the plug, which contacts the chassis of the stereo.

Integral

If this is the case you are not grounding the antenna, the antenna is the center wire of the coaxial cable. The shield should be ground, I do not think it is wise to rely on the antenna shield as the sole ground, some systems may rely on the stereo to provide the ground to the antenna shield. (not likely but, possible)

chroot

Integral,

Hence my confusion. I thought megashawn was indicating the actual antenna itself was grounded to the chassis -- and it's not. You wouldn't be able to pick up radio waves very well at all with a chassis for an antenna. I gave up and stopped participating in the thread.

Certainly you could ground your stereo with the coax sheild, but it's still probably not a very good ground. Ideally you'd like your ground to be as close as possible to the head unit itself; the longer the wire run, the larger your likelihood of picking up alternator whine. The power wire is not very susceptible to noise, because it's regulated and filtered inside the head unit anyway. The ground wire, however, is quite susceptible to picking up noise.

- Warren

chroot

There's also a good chance that the antenna shield conductor is connected to the head unit's internal ground through a few RF chokes or other power-supply isolation network. Such a network may not be designed to actually carry significant current, and thus may not be adequate to properly operate the stereo. I still wouldn't do it.

- Warren

Averagesupernova

If you connect the radio to a so-called proper ground, what is there that guarantees you that ALL of the ground current will go through it and not some of it going through the antenna shield? There is NO guarantee. I see it as not that much of a big deal. Most of the time an antenna connector has the shield connected right to the chassis of the radio. Running it through some kind of component is asking for a potential disaster. The reason is because when you have 2 wires running to different parts of the vehicle and both connecting to ground there is a chance (larger than you may realize) that a poor ground elsewhere on the vehicle can cause current to run into the antenna connector and out through the radios main ground. Not too likely any problem will develop when the antenna coax shield is connected right to the chassis during this type of failure but if it were connected to some sort of component, the current would most likely fry that component.

chroot

Averagesupernova,

What do you mean by "component?" Your argument is precisely the reason the two grounds would be isolated with an inductor or other network. The two grounds may in fact be somewhat different. While you want the two grounds to remain at nearly the same potential, you want your current to flow through only one.

- Warren