Engine speed related radio hum/distortion in AUX

Discussion in 'Communications And Radio' started by TQuentin1, Jan 24, 2013.

  1. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    OK folks. I have a significant hum/distortion when playing my Sirius radio through my AUX port on the front of my UC radio. The hum/distortion is RPM related as the pitch of the distortion changes with the engine speed. This problem is NOT there when playing the satellite radio through the FM receiver. My next step is to plug my phone into the AUX port and see if that has the same hum/distortion as the satellite radio.

    I have swapped out the radio with Radio Sound, so I do not think it
    is the radio. Any of you folks had a similar problem and solved it?

    TQ
     
  2. Slo-Ryd

    Slo-Ryd Junior Member Contributor

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    What your getting is rf interference through the 12v positive of the radio or Sirius unit. If your Sirius radio is pulling power through your 12v power port/cigarette lighter, it'll usually cause this hum. The only soultion is usually to install a Noise Suppressor inline with the positive side power feed. This would require getting in behind the inner fairing if it's on your Ultra to wire it in. There may be a magnet style split two piece rf supressor that would go around the power lead of your Sirius power plus, but they're hard to find and I haven't seen one in years. Google "12v noise suppressor" which should be available at Radio Shack or most automotive supply stores in the car audio section.
     
  3. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    I actually have the pos and neg leads from the Sirius radio run directly to the battery terminals.

    TQ
     
  4. Slo-Ryd

    Slo-Ryd Junior Member Contributor

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    It'll still pick up the interference that way. That's an easy fix to wire in the noise suppressor then since you have access to the hot lead going to the Sirius radio. A noise filter shouldn'r be any more that $10 or so and will eliminate the problem. I was having the same issue with my Ipod when pulgged in to charge thru the cigarette lighter while playing at the same time. I put the suppressor on the 12v side going to the cig lighter/power port and it went away. Experience from installing car stereos ages ago :)
     
  5. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    I agree with BigAl's assessment. I had a problem with an XM unit in my truck going from FM converter to aux-in. The hum is from the power to the XM unit. noise suppressor fixed it. Something about the gain structure of the aux vs. FM. It is a hotter signal and picks up the noise.
     
  6. Dandekar

    Dandekar Member

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    Neg to battery terminal is too long.
    Shorten the neg leg to the nearest ground point.
     
  7. Slo-Ryd

    Slo-Ryd Junior Member Contributor

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    Yup, another possible cause but I've found that even when a good ground was established, I'd see the noise in certain instances. Spiral wound metal spark plug wires were notorious for that problem, especially when you had your radio on am. Whined like crazy in an old Nova I had. That's what led to noise suppressed carbon core wires in the late 70's or so. Some of the new aftermarket "performance" wires out for our bikes currently have gone to copper core or stainless and will cause a bunch of rf whine as well.