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Thread: Protecting from EM Radiation

  1. #11
    Raw Wave
    Join Date
    Nov 2009
    But if that resistance were significant, the M4 would not operate.

  2. #12
    Variable Bitrate
    Join Date
    Nov 2006
    Rubidoux, CA
    Quote Originally Posted by OldSpark View Post
    But if that resistance were significant, the M4 would not operate.
    Not entirely true - a switching power supply can handle a very wide input range and not affect it's output regulation. The fact is, it's pretty much impossible for a standard RF broadcast to induce enough current on a car battery to cause the voltage to jump more than double the nominal battery voltage. The induced current would be shunted right through he battery, and the voltage would never be allowed to climb that high.

    What he is describing is one of two things - either there is something preventing that induced current from shunting without generating a voltage spike (high resistance), or he is not really getting a voltage spike on the line, but his meter is.
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  3. #13
    Raw Wave
    Join Date
    Nov 2009
    Yes, it is well known that power lines can pick up EMI, but that is not path resistance. Impedance maybe, but not resistance.
    Batteries are BIG capacitors and hence snub AC (as in the typical relatively low frequency of alternators - eg, up to 1kHz etc) though that might not mean high frequencies (I'm not sure, but electrolytic caps do not snub/suppress/quench HF noise...).

    But I think you and I are in agreement. I too wonder if the voltmeter is picking up HF voltage (hence the "rubbish" reading) as well as EMI injecting the M4 to cause shutdown since IMO they are the most likely, and hence my replies.

    I was going to ask what sort of radio tower - presumably not ULF Navy, but maybe HF or UHF and higher comms & radar.
    But I'd suspect the M4 since they may be uncommon - ie, I expect PCs to be more common and hence if interference from that radio tower was a problem, it would be reasonably well known.

    But I am not familiar with M4 over-voltage shutdown, nor whether the OP's PC shuts down due to overvoltage (in my experience many do not, but that may well have changed - after all, there enough supervisory chips in common usage).

  4. #14
    Constant Bitrate Rickk's Avatar
    Join Date
    Feb 2013
    Western Massachusetts
    Old thread I know, but clip-on ferrite beads (#31 material works well) every half foot or so on the wires coming from and going to the PS may help a bit.

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