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OT: Possible causes of AM car radio static?

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  • OT: Possible causes of AM car radio static?

    Car AM radio sounds great when engine is not running. Turn on engine and get popping static that corresponds to engind rpm's. Happens when sitting still too so it's not static buildup from tires.

    This car has a generator. (Brushes need replacing?)

    What are some possible causes?


  • #2
    Put a capacitor across the generator output line to earth (watch the polarity!). I think your description of a 'popping' sound is more likely to be HT RFI, this will need suppression HT leads or suppressed plug caps (or both).

    If the problem persists then Haggis forced into the speaker cones works well!



    • #3
      Dont listen to a word RR says he knows nothing about haggis whatsoever Alistair

      [This message has been edited by Alistair Hosie (edited 06-28-2004).]
      Please excuse my typing as I have a form of parkinsons disease


      • #4

        Sorry. I'm drawing a blank this morning. HT = ??? (High Tension as in plug wires?)

        If yes, then are you referring to resistor plugs and plug wires?

        I'd try the haggis but the smell might be too much after a couple of weeks with high humidity and high temperatures.


        Another fact that may enter into this is everything was crisp and clear as a bell then one day this started.

        [This message has been edited by pgmrdan (edited 06-28-2004).]


        • #5
          Have you tried new wiper blades ?

          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


          • #6
            Yes, HT = High Tension, sorry I did not explain. RFI = Radio Frequency Interference, the other oft quoted expression in this case can be EMI which = Electro Magnetic Interference.

            Has the weather changed? Atmospheric conditions can drastically affect/effect things like RFI. High pressure, dry air will cause more problems.

            Haggis, on the other hand, is not affected by anything. ......Although I have to admit I do like Haggis, especially if it has a smidgen of pure malt poured over it!



            • #7
              I kid you not. Try spraying some WD40 on the spark plug wires.

              [This message has been edited by Evan (edited 06-28-2004).]
              Free software for calculating bolt circles and similar: Click Here


              • #8
                Yes, it is RFI. Not necessairly HT. Possible cures include:

                Replaceing spark plug wires

                Adding capacitors from the 12 volt power leads to the radio to ground. Use both a 0.1uF ceramic and 50uF or 100uF electrolytic in parallel. Do watch out for the polarity on the electrolytic. Do this as close to the radio as possible.

                Check that all connections under the hood are good ELECTRICAL connections. I watched an auto mechanic connect a groud wire once and it made me cringe. Wire was filthy and corroded. The metal he attached it to was painted and that was covered with grease and grime, and he didn't even tighten the screw well. He didn't have a clue about electricity. (I did redo it.)

                Check the antenna lead and make sure it's tight at both ends. If necessary, replace the antenna.

                Paul A.

                Paul A.
                SE Texas

                Make it fit.
                You can't win and there IS a penalty for trying!


                • #9
                  Something like this starting suddenly is usually a bad connection that has developed. Make sure the antenna mounting on the body is good. There should be a good ground connection there. Sometimes, the short ground lead (it's a 10 or 12 gauge wire) that goes from battery negative to the body metal is at fault. This is a good junction to clean up anyway, even if it doesn't affect the radio. Other than that, if the noise appeared suddenly, there could be a noise suppressor that has lost a connection due to vibration. Sounds to me like a connection has gone bad, possibly from having gotten wet, then dried. Any junction that is bolted or screwed to ground via body metal is suspect.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                  • #10
                    I had a problem recently with my PT Cruiser. At first I put it down to the air conditioning compressor kicking in and sucking power. After a bit of testing it became clear that was not the problem. I took it to the dealer (yeah, I know, I could have saved money and done it myself BUT, have you looked under the hood on one of these?????).

                    The dealer quickly found the wires had been chewed by a varmit of some sort. He said it happens all the time. A similar situation could result in RFI on the radio.
                    Free software for calculating bolt circles and similar: Click Here


                    • #11
                      Look for a small capacitor mounted on or near your voltage regulator or your ignition coil. If the capacitor is used with your ignition coil, it should be attached to the positive terminal of the coil.

                      Open circuit failure of a capacitor used at either location will cause AM static which increases in pitch as you increase engine RPM's. You can disconnect one end and do a crude functional check with an analog meter set on an Ohm scale.

                      Evan, I'm interested in the WD-40 remedy.
                      Any idea as to why it is effective?


                      • #12
                        This car has new spark plugs, plug wires, points, condenser (that's 'old school' for capacitor ), rotor, and distributor cap. All high quality stuff from a place specializing in aircooled VW's. That's why I'm suspecting some older part first.

                        Alan, when you mentioned a capacitor near the ignition coil are you talking about the one on the distributor?


                        • #13
                          Are you sure they are suppression or carbon core wires, as opposed to solid or copper core? Are the spark plugs the resistor type? If the answer to both questions is yes, carefully double check your connections on both ends of the wires to be sure you have good contact. Use silicone grease (dielectric tune-up grease) on both ends of the boots to be assured that there is no leakage from the wires. Also route them with looms so that they are not touching each other, and are spaced about آ¼â€‌ from any metal. They will last much longer if you take the time to do this.
                          I am guessing that this problem started or worsened after the tune-up?
                          Location: North Central Texas


                          • #14

                            I'm about 99% sure I have resistor plugs and plug wires. I'll double check.

                            The problem arose about 4 or 5 months after the tune up with very, very few miles on the components (still new, IMHO).

                            I've checked connections and they're all good. Usually, if plug wires are arcing I can see and hear them in the dark but that's not happening here.

                            I'll try moving the plug wires around (with a stick ) while one of my kids is listening to the radio and see if the popping goes away. Unfortunately the looms are missing.

                            After that I'll try putting the old condenser on to see if that helps.

                            No one mentioned that the generator brushes could be causing it so I'll ignore that.

                            Can a voltage regulator do this when it's beginning to go bad?


                            • #15
                              WD40 is Water Displacer. Water can get trapped under the boots and cause corrosion and high voltage leakage. It says right on the can "To restore wet or flooded equipment such as: Engines, Spark plugs...."

                              Dan, a problem with the generator will create a whine at a much higher frequency than the ignition. It will of course change with engine speed. One question: If this is an old vehicle without a high energy ignition system you can safely pull a plug wire off, one at a time and short it to ground (with a spare plug). Does doing so change the noise?

                              [This message has been edited by Evan (edited 06-28-2004).]
                              Free software for calculating bolt circles and similar: Click Here