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

Discussion in 'Electronic Repair' started by [email protected], Sep 17, 2005.

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  1. Guest

    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

  2. Guest

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

    TimPerry Guest

    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)
  4. w_tom

    w_tom Guest

    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.
  5. w_tom

    w_tom Guest

    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.
  6. Jim Adney

    Jim Adney Guest

    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.

  7. Guest

    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.
  8. w_tom

    w_tom Guest

    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.
  9. Ken Weitzel

    Ken Weitzel Guest


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

    Take care.

  10. TimPerry

    TimPerry Guest

    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.
  11. Guest

    Given that it is a Chrysler product, likely with the Infinity sound
    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.
  12. Guest

    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
  13. Guest

    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

    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!
  14. DaveM

    DaveM Guest

    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.


    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!!
  15. Guest

    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
  16. w_tom

    w_tom Guest

    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

    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.
  17. TimPerry

    TimPerry Guest

    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
    i find that the added interference make Rush Limbaugh slightly more
  18. TimPerry

    TimPerry Guest

    Another poster and I suggested sniffing around using a small AM
    an alternative is to build a "sniffer" antenna. this is a small loop
    wound at the end of non conductive rod. the coax connects to the car
    (or a portable) you fish around the engine with this in relative
    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
    i find that the added interference make Rush Limbaugh slightly more
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