My AM car radio has tons of static when the engine is running. The
thing is useless when the car is on or even if the key is turned to the
on position right before you start the car. It's fine if you turn the
key to the aux position.

Another clue...

When I turn an electrical motor in the car on and off, it sometimes
reduces the static level...but never eliminates it. And then when I've
fiddled with something and reduced the static, I'll hit the brakes, and
the brake light will trigger the static onslaught again.

I have taken the radio out, and checked the antenna connection as well
as used jumper cables to ground the grounding bolt. No significant
improvement.

Thoughts?

Bad ground. Not to the radio but to the other equipment.

wrote in message
ups.com...
My AM car radio has tons of static when the engine is running. The
thing is useless when the car is on or even if the key is turned to the
on position right before you start the car. It's fine if you turn the
key to the aux position.

Another clue...

When I turn an electrical motor in the car on and off, it sometimes
reduces the static level...but never eliminates it. And then when I've
fiddled with something and reduced the static, I'll hit the brakes, and
the brake light will trigger the static onslaught again.

I have taken the radio out, and checked the antenna connection as well
as used jumper cables to ground the grounding bolt. No significant
improvement.

Thoughts?

the cars onboard computer or instrument cluster is generating RF.

"fish" around with a portable radio to localize the problem.

recheck the car antenna system. try a RF choke on the DC power wire(s)

Or the regulator inside the alternator is a source of RF.
There are just too many other potential reasons to but only
blame a computer or instrument cluster.

Cars do not come from the factory with static. Number one
reason for static would not be cured with RF choke.
Furthermore, the RF choke would not identify noise entering
due to bad ground. Better is to first learn what has been
changed - to have created this problem. To have better help
from the newsgroup, the OP must provide model, year, what is
and is not original in the vehicle, what has changed, etc. By
rationing facts, his responses can only be speculative - not
very helpful.

TimPerry wrote:
the cars onboard computer or instrument cluster is generating RF.

"fish" around with a portable radio to localize the problem.

recheck the car antenna system. try a RF choke on the DC power wire(s)

"w_tom" wrote in message
...
Or the regulator inside the alternator is a source of RF.
There are just too many other potential reasons to but only
blame a computer or instrument cluster.

most likely the comp.


Cars do not come from the factory with static.

you have obviously never worked in the auto sound biz.

Number one
reason for static would not be cured with RF choke.

rf may enter through the power and/or clock wires if not adequately bypassed
in the radio

Furthermore, the RF choke would not identify noise entering
due to bad ground.

bad ground usually means no power at all.

Better is to first learn what has been
changed - to have created this problem. To have better help
from the newsgroup, the OP must provide model, year, what is
and is not original in the vehicle, what has changed, etc. By
rationing facts, his responses can only be speculative - not
very helpful.

TimPerry wrote:
the cars onboard computer or instrument cluster is generating RF.

"fish" around with a portable radio to localize the problem.

recheck the car antenna system. try a RF choke on the DC power wire(s)

many car radios have an antenna trim adjustment for the AM section. when
this is misadjusted the AM signals are weaker and noise is greater.

Given that it is a Chrysler product, likely with the Infinity sound
system.
There is a very good chance the the ground to the fuel pump, power
regulator, or other main system ground in the car has become corroded
and is no longer a good ground.

I have fixed a couple with bad ground to the fuel pump or the blower
motor that was causing radio interference in the past. Ground would
read a few small ohms resistance, but it was enough for the motor noise
to be radiated and the motor would still run.

wrote:
Given that it is a Chrysler product, likely with the Infinity sound
system.
There is a very good chance the the ground to the fuel pump, power
regulator, or other main system ground in the car has become corroded
and is no longer a good ground.

I have fixed a couple with bad ground to the fuel pump or the blower
motor that was causing radio interference in the past. Ground would
read a few small ohms resistance, but it was enough for the motor noise
to be radiated and the motor would still run.

Your are on the right track. we need to know if the noise changes with
engine speed, vehicle speed, interior lights on, esterior lights on,
doors open or closed to light the interior lights, etc. A bad ground
on some other piece of equipment is the most likely item. My Nissan
pathfinder makes AM radio weak stations clicks as a function of vehicle
speed. It must be the electronic odometer, and I have learned to live
with it. I have seen bad fuel pump grounds, ceiling lights with poor
grounds, etc. Sionce this vehicle has an electric antenna (presumable
to make it go up and down, I would look for a poor ground connection in
the vicinity of the antenna and along the route the antenna wire takes
from the antenna to the radio. ALso, as one poser said, take a small
transistor radio, tune to a weak station, and sniff around the vehicle
to see if you can pick up any noise that sounds like the noise on the
radio. Good detective work will eventually find the answer.

As an EMC engineer with 40+ years of experience, once you find the
trouble, it will be obvious what is going on. I once tracked a
malfunctioning electronic telephone office source of problems to trains
turning their transmitters on to call the dispatcher just as they went
past the back of the telephone office. The malfunctioning processor
only happened when the transmitters on the trains were turned on at a
particular spot where the antenna pointed right at the telephone office
as the train went by. A little conductive paint on the back wall of
the telephone office provided enough shielding to stop the problems.
SO, anything is possible.

H. R.(Bob) Hofmann

Manufacturer's original equipment or some third party
installation? It simply takes an antenna plug not exactly
sized to the radio socket. That intermittent connection then
creates radio static. There are a long list of other reasons
including loose ground to chassis. There is very good reason
why grounds are not just put anywhere. Does the antenna coax
shield somewhere make contact with the chassis ground? That
too would create static problems.

Your car radio should receive major (50,000 watt) AM radio
stations even 100 miles away. If not, your radio may be a
discount special, or you have loose connectors, or other
possibilities are just too numerous to mention here.

Remember wire is just another antenna. Even where a radio
is grounded in relation to everything else can create
interference. However number one on your list would be an
intermittent antenna wire maybe because the antenna lead plug
does not quite match the antenna lead socket connector.
Welcome to an art.

wrote:
My AM car radio has tons of static when the engine is running. The
thing is useless when the car is on or even if the key is turned to the
on position right before you start the car. It's fine if you turn the
key to the aux position.

Another clue...

When I turn an electrical motor in the car on and off, it sometimes
reduces the static level...but never eliminates it. And then when I've
fiddled with something and reduced the static, I'll hit the brakes, and
the brake light will trigger the static onslaught again.

I have taken the radio out, and checked the antenna connection as well
as used jumper cables to ground the grounding bolt. No significant
improvement.

Thoughts?

On 17 Sep 2005 14:42:10 -0700 wrote:

I have taken the radio out, and checked the antenna connection as well
as used jumper cables to ground the grounding bolt. No significant
improvement.

When you checked the antenna, did you also verify that the antenna
coax outer shield made a good connection to ground at the base of the
antenna? It is important that BOTH antenna lead conductors be
connected well.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Thanks for all the advice. Let me fill in some more details. The radio
is OEM in a 95 Jeep Grand Cherokee Limited. It has some sort of
amplified output and an electric antenna. The problem has been more
progressive than sudden. Only affects reception when the car is 'on'
(running or key in the on position). The antenna is original, and the
connection to the radio appears good. Something else not grounded and
giving off static is a possibility...would have to be something that
powers up just with the 'on' switch, not just when running (may
eliminate alternator). If it is a 'ground leak,' might that explain how
sometimes fiddling with an electric switch seems to reduce the static?
Maybe the other switch grounds some of the static causing emission? Not
really knowledgeable about electronics.

You are still making assumptions without facts. For
example, if the key is on but engine not running, then
regulator electronics inside the alternator can still be
radiating RFI. Obviously. Engine need not be turning for
those electronics to be functioning.

Furthermore, its not about something "not grounded and
giving off static". It can also be "something grounded
differently and therefore radiating noise". Noted earlier -
every ground wire is also an antenna. Vehicle electronics
must be grounded to work. Therefore even working electronic
device that radiates noise is also grounded.

There is no way to visually confirm a connection - "the
connection to the radio appears good" and yet that antenna
connection is not between two connectors of the same size. A
failed antenna wire connection will always 'appear good'.

Welcome to an art where you cannot make blanket
assumptions. Your first efforts should only be on confirming
antenna integrity as I and Jim Adney have noted. This, of
course, assumes everything is original Jeep equipment - a
necessary fact which has not been stated. For example, if
that amp is after market, then there is a grounding change -
or other problem.

Again, welcome to an art where everything you do must be
understood experimentally AND must also be in total agreement
with theoretical concepts. Your assumptions such as the
connector 'looks' good is begging to not have a solution.
Good reason why EMI/RFI experts have decades of experience.

wrote:
Thanks for all the advice. Let me fill in some more details. The radio
is OEM in a 95 Jeep Grand Cherokee Limited. It has some sort of
amplified output and an electric antenna. The problem has been more
progressive than sudden. Only affects reception when the car is 'on'
(running or key in the on position). The antenna is original, and the
connection to the radio appears good. Something else not grounded and
giving off static is a possibility...would have to be something that
powers up just with the 'on' switch, not just when running (may
eliminate alternator). If it is a 'ground leak,' might that explain how
sometimes fiddling with an electric switch seems to reduce the static?
Maybe the other switch grounds some of the static causing emission? Not
really knowledgeable about electronics.

wrote:

My AM car radio has tons of static when the engine is running. The
thing is useless when the car is on or even if the key is turned to the
on position right before you start the car. It's fine if you turn the
key to the aux position.

Another clue...

When I turn an electrical motor in the car on and off, it sometimes
reduces the static level...but never eliminates it. And then when I've
fiddled with something and reduced the static, I'll hit the brakes, and
the brake light will trigger the static onslaught again.

I have taken the radio out, and checked the antenna connection as well
as used jumper cables to ground the grounding bolt. No significant
improvement.

Thoughts?

Hi...

A perhaps interesting experiment might be to pull the fuel pump
fuse and see if the static disappears with the key on.

Take care.

Ken

Another poster and I suggested sniffing around using a small AM
battery-operated transistor radio. The OP doesn't say if he has
tried
that or not.

H. R.(Bob) Hofmann


an alternative is to build a "sniffer" antenna. this is a small loop
antenna
wound at the end of non conductive rod. the coax connects to the car
radio
(or a portable) you fish around the engine with this in relative
safety
looking for the spot that makes the loudest similar noise.

for what it worth my 2000 cherokee exhibits similar issues. i get
clicks and
pops when turn signals are in operation. sometimes when wipers are in
operation.
i find that the added interference make Rush Limbaugh slightly more
palatable.