Neon RFI

Discussion in 'Ham Radio Discussions' started by N3HGB, Jul 21, 2020.

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  1. N3HGB

    N3HGB Ham Member QRZ Page

    Do old fashioned neon bulbs produce RFI? My Google-Fu is failing me, you get 10,001 hits on CFLs, modern LED bulbs, computer case neon bulbs with noisy little inverters, and so on.
    I am thinking more of the little NE-2s and bigger NE-42s that have no power supply at all. How about neon signs like a bar sign with a high voltage transformer? I have to think those would make RFI, but I have not tested one.
  2. WZ7U

    WZ7U Ham Member QRZ Page

    I'm under the impression that a property functioning assembly would be rf clean but in reality the opposite is most likely. Check with a pocket AM radio.
    WQ4G and K4AGO like this.
  3. AI3V

    AI3V Ham Member QRZ Page

    Not only do they produce rfi, but once upon a time they (gas discharge tubes) were used as a standard noise source for testing receiver sensitivity:

    NL7W likes this.
  4. K4PIH

    K4PIH Ham Member QRZ Page

    Old fashion neon bulbs are different than fluorescent lights, or so I thought.
  5. N3HGB

    N3HGB Ham Member QRZ Page

    They are different, The little NE-2 and the NE-42 are just two electrodes in a glass bulb full of neon. There is no ballast or inverter or anything, just a resistor to limit the current. The bigger neon tubes use 10/15/20 kilovolt transformers with a current limiting function in how they are wound. The transformer itself would make no RFI, but a foot or three or five of neon plasma, it might make a lot, I really don't know.
  6. N8YQM

    N8YQM Ham Member QRZ Page

    I'm thinking they can't make that much RFI, old voltage regulator tubes were basically neon bulbs designed to glow at a certain voltage. They were often used to regulate voltage for oscillator circuits for stability.
  7. AI3V

    AI3V Ham Member QRZ Page

    You would be wrong.

    ANY GAS DISCHARGE device generates rfi.

  8. NL7W

    NL7W Premium Subscriber QRZ Page

    It's colored continuous lightning in a bottle (tube)!
    Of course it's noisy!
  9. W9BRD

    W9BRD Ham Member QRZ Page

    Maybe, but in 50+ years of working with radios I've never heard RFI produced by neon bulbs or VR tubes. Perhaps if I got a probe very close...but that's not how they or my antennas are used.

    Gas-discharge tubes can be used in so-called relaxation oscillators up to at least the AM broadcast band; and oscillating at lower frequencies they will generate harmonics that likely make it up MF and maybe higher.

    But if VR tubes were serious or even moderate sources of RFI, you'd've seen that mentioned across decades of radio handbooks, and they would be scarce in receiver designs from those days -- which, in better receiver and transceiver designs, they are not.

    Mercury-vapor rectifiers are something else again.
    WQ4G likes this.
  10. W4IOA

    W4IOA Ham Member QRZ Page

    Hear noise on the radio?
    *-turn off possible neon light.
    Noise gone?
    *-found it
    Noise still there?
    *-it's sumtin' else

    Take an AM radio around to search (or use your ht)
    Turn off all the breakers then on one by one until you find the offender
    NL7W likes this.

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