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No FM Radio when CarPC is on

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  • No FM Radio when CarPC is on

    Hey guys, I have a little problem here.. I did a quick search and found a couple of people have had the same issue, but I haven't found a fix yet.

    Basically, I've got my CarPC run through my head unit using it's internal amp. Everything is fantastic, until I try to listen to FM radio on the head unit (I know, who uses FM radio anymore if you have a carpc.. lol)...

    I want to use the head unit because I want an easy way to get FM, and I want to use the HU's volume knob to control the levels in the car... which all work great and working perfectly.

    Anyway, everything works just how I want, except when my PC is on, I lose complete reception on my FM tuner.

    I've got my PC hooked up to the remote connection behind the HU which triggers the PC's power supply.. if I disconnect this wire, and wait for the computer to shut off, then I get my reception back (but not until the PC is off completely).

    I've tried my stock remote wire... I've tried the remote wire coming out of the back of my HU.. I've tried removing the remote wire completely.. still nothing seems to help.

    The HU is powered off of the stock radio harness.

    The PC is powered off of a dedicated line straight to the battery, and grounded to the body of the car.

    I get no radio hiss or whine otherwise..

    do you guys have any ideas for me?


    Also, I've tried disconnecting the power from the LCD (xenarc 700idt), and removed the aux input into the HU and neither of these help at all.
    Last edited by Eldorado; 03-07-2011, 05:32 PM. Reason: added more info

  • #2
    That remote wire is probably grounded through the FM antenna. That would cause enough EFI in the antenna to screw up any FM reception.
    Although that wouldn't explain how you lose FM reception when you use the "stock remote wire"... What is that, exactly?

    You say you have the PC audio going through the headunit, you don't specify how the audio signal from PC gets to the headunit. AUX input? FM modulator? Cassette adapter?

    Also, where is your antenna and what type is it? Could you have an antenna embedded in the window/defroster by any chance?
    Have you looked in the FAQ yet?
    How about the Wiki?

    Under normal circumstances, a signature would go here.


    • #3
      hmm.. if the remote wire was grounded through the antenna, then it should go away when i disconnect the PC from it, shouldn't it?

      what i mean by the stock remote wire is the switched 12V accessory lead coming from the stock stereo harness that is only juiced when the car is on.

      I have the audio going from the PC via the 3.5mm sound card output to RCA connectors going into the AUX input on the back of the Pioneer deck... I've tried removing this connection, and the problem is still there (remember, I only have a problem with the FM reception, everything else is crystal clear).

      Antenna is a manual, non-powered, non-amplified pull-out antenna in the driver's side A-Pillar... it's a Mazda Protege, 2001.

      Thanks for the reply!


      • #4
        So, when the computer is on, there is no audio at all from the radio when it's selected to FM? Or do you get really crappy reception?

        What head unit do you have?
        1999 Mercury Grand Marquis GS with: ASRock E350M1 w/4GB RAM, 80GB Intel SSD, Opus DCX3.120, Visteon HD Radio + HDR-USB, PL-18N wifi, OBDLink Scan Tool, BTA6210 BT, BU-353, Win 7 Ultimate, CF 4.0, Alpine MRP-F240 + MRP-T220, RF Punch 1572s, Kicker 8" Comp.


        • #5
          it's a Pioneer 3100UB i believe is the model number. I bought it specifically for the rear AUX.

          i still get sound, but it's horrible reception... you can barely make out what is on.

          As a temporary measure, I've installed a switch on the remote line going to the computer's power supply so i can switch it off to mimic the car being turned off, which in turn starts the computer into the shutdown procedure whenever I want to listen to the radio.... and ran the switch to inside the glove box... but this is a band-aid.

          it's not all bad though, considering my computer takes about 8 seconds to boot, i dont have to wait an eternity if i wanna switch back to the PC...

          any other help is appreciated to fix this.


          • #6
            I'd look at where the factory antenna lead is run in your car, and see if you have run your power or remote lines next to it, or if you have your computer sitting on top of it.
            1999 Mercury Grand Marquis GS with: ASRock E350M1 w/4GB RAM, 80GB Intel SSD, Opus DCX3.120, Visteon HD Radio + HDR-USB, PL-18N wifi, OBDLink Scan Tool, BTA6210 BT, BU-353, Win 7 Ultimate, CF 4.0, Alpine MRP-F240 + MRP-T220, RF Punch 1572s, Kicker 8" Comp.


            • #7
              remove the pc, and all will be fine...

              course you might not like to hear that, but something about it in generating RFI

              prob the power supply... can you power this pc another way for some testing....

              get that supply far far away from the antenna/radio

              "Did you test it in carwings??"

              Sun, Come shine my way
              May healing waters bury all my pain
              Wind, Carry me home
              The fabric of reality is tearing apart
              The piece of me that died
              Will return To live again


              • #8
                What car do you have?

                What computer dc-dc power supply?

                It usually points to a noisy power supply and can be checked by using a household power supply. The majority of all complaints with this issue all had one thing in common, M2-ATX and ituner never responded to my inquire about RFI.
                System always under construction


                • #9
                  forum member mickz has figured out a possible solution to some of the noisy power supplies-- technically it is more of a work-around:
                  this is the start of his discussion:
                  My OLD 2001 Mitsubishi Eclipse GT:
                  "The Project That Never Ended, until it did"

                  next project? subaru brz
                  carpc undecided


                  • #10
                    I noticed that forum member also has a Honda. I don't know why, but for some reason, the interference problem is multiplied in Hondas. There is something funky going on in Hondas. It is just a bad combo. I have tried my buddies m2-atx in my car and still have no GPS issues and maybe an ever so slight FM reception reduction, but it still works. In his car, he had to keep the GPS up front and his power supply in the trunk, but his radio reception was gone. That is why I said it could be the car AND the power supply used.
                    Last edited by durwood; 03-09-2011, 09:07 AM.
                    System always under construction


                    • #11
                      I've got a 2001 Mazda Protege.
                      The Power Supply I have is, I believe, a M4-ATX 250W power supply.

                      The antenna is routed through the driver's footwell, up to the Driver's A-Pillar. The computer is located under the passenger seat, with the power line coming up under the center console.

                      Interference from the power supply sounds like it could be the cause... but that seems like an awfully big distance to travel, a good 4-5 feet from antenna to computer...


                      • #12
                        Well it was found that the interference travels on the power wires (they become the broadcasting antenna), so it's really everywhere. Sounds like you need to try the aluminum case + feed-thru cap fix, or try the DS-ATX. I am curious if all power wires need that fix, or just the 12V or ground or both.
                        System always under construction


                        • #13
                          it's not ideal, but I've learned to get by using the switch to flip it on... Just means I need to wait 8 seconds before using the PC, or 8 seconds before listening to the radio.... like I said, not ideal.. but acceptable.

                          thanks for all your input guys. I've read the forums quite a bit over the last couple of years, but haven't posted much... glad to know that there are people here to help.