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FRS radio interference from Galaxy DX939

Discussion in 'General CB Services Discussion' started by Cutlass327, Oct 11, 2019.

  1. Cutlass327

    Cutlass327 Active Member

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    I figured this would fit here better than the FRS section, since it is an issue from the CB.

    I tried posting a video but it keeps saying "file too large" at under 50MB, but it is my FRS radio on ch15, and it is picking up something from the DX939 unless I touch the faceplate of the CB. The face backlighting is unplugged, as it just whines when connected. I was thinking I could try grounding the chassis to the cabinet under it, as I first noticed it would stop when I touched the faceplate and then the metal filing cabinet it is sitting on. But it didn't change if I touched the mounting screws, only the chrome front.



    I had tried a 2nd video, shorter, but still too big. I noted that it be only happens on CB ch18 and 21.

    Any ideas?
     

  2. Cutlass327

    Cutlass327 Active Member

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    The sound on the FRS radio sounds like the noise on CB 16, a high pitch whine.
     
  3. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Is it a mobile installation? Alternator whine? Does it vary with engine speed? If if does it is the alternator.
     
    357magnum likes this.
  4. Cutlass327

    Cutlass327 Active Member

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    No, it is a base setup. I have a DX88HL in the same setup, it doesn't have the same issue.
     
  5. Road Squawker

    Road Squawker Sr. Member

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    What kind of PS is the CB on? linear or switching?
     
  6. nomadradio

    nomadradio Analog Retentive

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    Has to be a clue hiding behind that observation.

    Just don't know what it is.

    73
     
  7. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Station grounds, If you don't have any get some!
     
  8. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    Harmonics of IMD?
     
    midnight special likes this.
  9. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Could be radiated noise from an IF.
     
  10. nomadradio

    nomadradio Analog Retentive

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    FRS channel 15 is 462.550 MHz.

    Divided by 28 gets you (almost) 16.52 MHz.

    The radio's PLL pumps this frequency into the transmit and receive mixers on CB channel 21.

    Just how much of that leaks out of the radio, who knows? The 28th harmonic sounds kinda far fetched, but it sounds like a maybe.

    73
     
  11. Cutlass327

    Cutlass327 Active Member

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    This is the power supply.

    There is a ground lug on the case of it, I have a 8ga wire (the same I am using for power/ground supply) going to this lug from one bracket screw of the 88HL which is attached to the top of the 939 with hardware strap to all 4 bracket screws, so the exterior case of both radios are grounded to the power supply. This is why I do not understand it, as the chrome plated plastic faceplate is grounded (accidentally have shorted power wire to it before, so I know well grounded).
     

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  12. Chevboy0167

    Chevboy0167 Well-Known Member

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    Having the radio cases grounded to that lug on the power supply, aren't you mixing the RF grounds of the radios with the supply case ground? Supply case ground is for short circuit/shock protection for us meat bags. Since the supply is a switcher, you may be inducing a very small current to the radio chassis.

    I could be all wrong about all this but try isolating each radio one at a time to see if that helps.
     

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