Car radio static...AM w/key on or running

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.

 

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)

 

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.

 

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.

 

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.

-

 

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.

 

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

 

most likely the comp.

you have obviously never worked in the auto sound biz.

Number one

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

bad ground usually means no power at all.

Better is to first learn what has been

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.

 

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

 

Since my last post, I have tried a number of things to try to isolate
the issue. I connected a new (non-electric) antenna, and grounded it
directly to the battery. I had the radio on w/lots of static and pulled
each fuse (including fuel pump) one by one. I had a jumper cable on the
battery ground and conected it to the alternator, engine computer,
sound amp and radio ground itself.

None of these made any improvement.

I'll try grounding the fuel pump as I could not easily locate it
yesterday.

As to other questions posted here...nothing else in the vehicle seems
to correlate with less or more static. But it is worse sometimes than
others. Which may be a result of the weather or other conditions making
for a better or worse ground connection somewhere.

I'll keep tyring!

 

The extreme noise problem significantly points to a broken ground connection
in the antenna circuit somewhere. The broken ground may be inside the
radio. You might open the radio case and closely inspect the antenna
circuit connections. You might find the shield connection broken where the
antenna connector or the coax cable from the antenna connector makes the
connection to the radio's PCB.

As an alternative, park a car with a normally operating radio close to your
car. Shut the other car off and start your car. Do you hear the noise in
the other car's radio? If so, the problem is probably in your car's high
voltage ignition circuit. Check the ignition coil, distributor, the spark
plug wires and the plugs.

Cheers!!

--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

 

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

 

Appreciate what was said about wire. The battery ground and
radio ground may be same to 12 volts DC. But they are
completely different to RF - your static noise. Grounding the
antenna to the battery would only worsen the problem.
Grounding the antenna to the battery suggests you are not
learning the underlying principles posted by others. Battery
ground and radio ground are different - as far as the antenna
is concerned.

Antenna ground must be to radio ground. A previous post
also about how coax ground wire must not contact other ground
such as chassis was making the same point. The radio ground
is connected to ground directly at the base of the antenna -
for same reason. And again, the antenna coax wire connector
may 'look' connected to radio antenna socket - and yet still
not be connected.

Even possible that the antenna socket inside the radio has a
cracked solder joint - therefore the antenna ground is not
connected to radio.

Again, you still have not specifically listed what is
installed from factory and what is after market - only making
it more difficult for every reply to be helpful. Where did
that amp come from? How is it grounded?

Of course you already have the Jeep's wiring diagram. You
cannot be locating this problem (easily) without a wiring
diagram.

For example, along with what hrhofmann posted: is it an
electric fuel pump? Fuel pump is not always on. You should
have learned that by now in you search for the noise source.
For example, pump often turn on only for a few seconds after
key goes to on. Then if no engine requirement for fuel, the
electric fuel pump turns off. Does the noise go on and off
with fuel pump?

Pull the fuse that is only for alternator regulator. Does
noise disappear? Same for engine computer. To accomplish
anything from this trick, again, that wiring diagram is
necessary since even some disconnects may not fully remove
power as you assume. You cannot assume anything. The vehicle
has many computers - not just an engine computer. Any one
could be a noise source. Vehicle has something like 50
motors. Which motor is always on only when noise is created.

The transistor radio idea also works as long as you don't
assume a linear relationship between volume of noise on radio
and amplitude of noise. You have not even told us if noise is
radiated, if it is common mode, or if it is differential mode
on AC wires. Just another part of breaking the problem down
into parts.

Don't even try to fix anything. You are too far away from
even considering a solution. As hrhofmann posted, "once you
find the trouble, it will be obvious what is going on."
Again, break the problem down into parts. Your only concern
first is 'source of the noise'. You don't even know if the
noise is radiated or carried via 12 volt wires. Any attempt
to solve a problem with your current 'no information' is
equivalent to spinning tires in quicksand. Your only concern
is to identify the noise or its incoming path - not solve it.
Trying to solve it would only make the problem more difficult.

 

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.

 

Another poster and I suggested sniffing around using a small AM

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.