Static on AM when charging phone in 300M

I would suspect a loose connection in the lighter wiring. I'm curious, why another 2000, why not upgrade?

mike hunt

PAul Newsman wrote:

Mike,

My original 300 was a lease. I liked it a lot and had low miles on it. Took great care of it. Unfortunately, the buyout on the lease was way higher than what I could get the car for on a lot with the same or less miles. I got my current 300 for $3k less than the lease buyout and it had 4k miles less on it. Chrysler financial really blew when it came to customer service and satisfaction. I got another 2000 because of the steep depreciation of the car. It didn't seem to pay to upgrade.

Paul

You might be able to wire a 300 pf capacitor between the + side of the cigarette lighter and ground to fix this. Just go to a ham radio store and tell them your story, they have had plenty of experience helping people to get noise in their car supressed. If this doesen't fix it, the problem is most likely noise radiating from the charger and cord. You can test this by getting some aluminum foil and grounding it then wrapping the charger and cord and phone up in it while they are on, and seeing if the noise goes away.

Ted

Thanks for the reply Ted. This car is still under warranty. Isn't this something they should be able to determine and repair? Like I said previously, this is the same charger I used in my last 300M and I didn't have any problem.

Thanks

Paul

Choke = inductor = choke.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

To be honest they can't. The problem is that the charger is putting out RF that has harmonics directly in the AM band. It is like you set up a bunch of mini am radio stations in your car all transmitting at once. Since the RF from the charger is more powerful than the RF from the regular AM radio stations, it is basically erasing the proper AM signals in it's vicinity.

The charger is quite obviously the problem. It should be shielded and it isn't. You can write a complaint letter to the FCC and copy the charger manufacturer, under US law, they are mandated to mitigate the interference. Of course, if they don't, and the FCC declines to get involved, you have no recourse except a civil suit. In most of these cases the FCC does not get involved unless they receive many hundreds of complaints about a particular item.

This actually points more to radiated RF from the charger instead of RF leaking back through the + power connection. Unfortunately this is more common of an interference problem. Your last 300M may have had for example a steel frame in the dashboard, the new 300M perhaps has plastic. It could also be that the antenna lead from the AM radio is of a poorer quality than the old car, or perhaps the antenna design is different, or maybe you have a bad ground from the antenna to the car frame.

Whatever it is, though, the law requires that all radio transmitters have FCC approval, and operate in an assigned band. As long as your charger is generating RF it is a transmitter, thus it falls under FCC jurisdiction, and clearly it has no assigned radio band. Thus it is illegal. While the older 300M may have had a better body structure/antenna positioning/whatever that made it less suceptible to the charger's interference, it's not Chrysler's problem, really, because the charger isn't supposed to be broadcasting anything.

Now, if your 300M's AM radio is getting interfered with by a bunch of OTHER stuff out on the road, that's a different story. Then you can get on Chrysler's neck.

Ted

I thought I read someplace that the 300M uses a RF preamp to boost the signal to the radio received from the antenna in the rear window ?

The charger noise might suggest a problem in this RF preamp or its connections and wiring or wiring to the antenna ?

Has the rear window ever been replaced on this car ?

Steve

Not likely to happen. The FCC regs are written very cleverly to allow them to excuse themselves from any involvement unless they *really*

*really* want to be involved (i.e., if it is a problem of very wide spread public awareness and it becomes politically expedient for them to get involved).

The *emissions* part of their regs. say that any device emitting r.f. energy can't ineterfere with proper operation of other devices. The

*susceptibility* part of their regs. say that any receiving device must not be affected by devices emitting r.f. So when they receive complaints, historically, and citing the regs., they simply tell the two manufacturers that they have a problem (since clearly, both violate the regs.) and they stay uninvolved.

As you point out below, this also may very well be a "conducted emissions" (interference transmitted thru the wires of the vehicle, r.f. ground loops, etc.) problem rather than "radiated emissions" (sent thru the air to the antenna of the radio) problem.

No - many devices legally emit r.f. energy without being classified as a transmitter and assigned a radio band. Microwave ovens, our computers, ultrasonic medical devices, etc. The regs. simply define amplitude limits for any given frequency (via a specified curve that varies in amplitude over the defined range of frequencies). The fact that the device emits some r.f. does not classify it as a radio transmitter in need of an assigned band for intentionally transmitting a signal like a radio station. That pretty much gets enforced in that samples of the production devices (or pre-preproduction samples) are taken to certified antenna ranges where they are tested over the specified bands of frequencies and tweaked until they pass. Future production devices must incorporate all the changes that it took to achieve the passing of the tests.

Once that is done, it is assumed that the future production devices meet the spec. (and that's a big assumption because repeatability between samples as far as r.f. emissions behavior is not always very high - we're talking very low levels that can literally get changed an order of magnitude by routing a single conductor differently on a p.c. board, or grounding a capacitor at a different point on the same ground plane) unless there is a big (think high visibility and politically expedient) reason to think otherwise - and simply receiving a (or several) complaint(s) from the field is not enough to cause the FCC to jump into action.

Unless the FCC has good reason to believe that something changed between the antenna range qualification and the present production devices, they are easily able to blame both devices without arbitrating if there is a complaint of interference. They do this by simply citing the catchall "thou shalt not interfere with other devices" and "thou shalt not be susecptible to emissions of other devices" rules. They don't have the budget to do otherwise even though technically they should. They mostly are involved with the qualification of the device and subsequent approval. After that, once in production, all bets are off, barring, as I said before, that it would be politically expedient for them to fix a high visibility real world problem. (You can imagine the politics that can occur if they try to force a large company to spend a lot of money on recalls and/or fixing a problem for future production if the product is not in the public limelight.)

Like the stepper motors at the car wash that I drive by every day interfering with my a.m. radio reception. It would be a waste of my time to contact the FCC about that.

BTW - Chrysler radios are known by auto manufacturing insiders to historically be the worst in the industry (Norht American anyway) for noise rejection.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

I merely mentioned the FCC in order to show how useless it would be. They aren't going to waste their time with a $15 cell phone charger.

However keep in mind with AM that noise rejection is very difficult. Most electrical noise is AM (ie: varying amplitude) rather than a carrier shift such as in FM or other modes of radio transmission. So even with the best AM receivers out there your still going to get interference if the transmitter is strong enough. It's why AM has been relegated to talk radio, these days mostly occupied by conservative fringe elements. (Is that why you listen to AM Bill? ;-) Maybe the FCC bureaucrats figure the more interference the better! :-) :-)

Really the best option if he doesen't want to buy another charger is to try working with some shielding or add in a cap to the + line. I hope he posts a followup, it would be interesting to see what the problem was.

Ted