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1323Re: [Raspberry_Pi_4-Ham_RADIO] Re: Powering the Raspberry & TNC.

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  • Jim Thisdale
    Apr 14, 2013
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      Most computer mother boards have switch mode regulators on the board to make all the various
      voltages needed for the processor(s), memory, north & south bridges, and various other hardware.
      Gamer & enthusiasts boards often tout how many regulators/phases they have.

      As for radiation, most of the noise is from the leads & tracks on the board of chips themselves,
      especially when they are unshielded. A 5, 3.3, or even 1.8 volt signal toggling on-off at a high
      rate can radiate quite a bit, with 32 or 64 bits wide all toggling at such high clock rates it will
      radiate a lot of hash.... Computers tend to generate & radiate a lot of hash that's one reason the
      better made ones have metal cases and metal shielding in key areas. The minor amount of noise/ripple
      out of the supply is miniscule compared to the hash from the computer it-self. If a supply is truly
      that noisy the noise/spikes on the power would be mistaken for data and foul up the processing.

      -Jim- N1JMM, KB1YPL_B
      Visit my Pi running ircddb, dvrptr, Apache & many other things:

      On 4/7/13 6:15 AM, JJ wrote:
      > On 13-04-07 05:49 AM, John B. Cundiff Jr. wrote:
      >> Every time any digital device switches from off to on it produces a small spike and every spike
      >> as harmonics or RFI ... you can never completely clean up the supply of a computer ...you must
      >> design the computer
      >> to live with the spikes and RFI.
      >> On 04/07/13, Ray Wells<vk2tv@...> wrote:
      >> John,
      >> It's more than just spikes.
      >> The National Semiconductor recommendation to "tame" the output of the LM2596 smps is to add a
      >> series inductor (10mH from memory) and a shunt capacitor. Whilst this may very well result in a
      >> power supply that will "please" the Pi, it will do absolutely nothing to suppress RFI, which
      >> requires techniques quite different from those that produce a clean DC supply. The problem is not
      >> insurmountable but would require some devotion to produce a supply that is both DC and RF clean.
      >> It can be done.
      >> FWIW, the problem, from a Pi perspective, isn't necessarily spikes. Some smps's produce a distinct
      >> sawtooth output under load and whilst there may not be any spikes, there may well be dips below
      >> the minimum working voltage of the Pi at the bottom of the sawtooth waveform.
      >> Don't believe for one moment that you can assess a supply as being "good" with a voltmeter,
      >> digital or otherwise. It is indeed a case where a picture is worth a thousand words and that is
      >> where the CRO plays its part. If you don't have a hardware CRO, use a soundcard based device.
      >> There is plenty of free oscilloscope software available online.
      >> Ray vk2tv
      >> On 07/04/13 18:03, John B. Cundiff Jr. wrote:
      >>> Wood not a simple choke ...maybe a torridal choke
      >>> suppress the spikes every one is worried about .
      >>> Put a big value filter capacitor afterwards .
      >>> Be a lot more portable .. simpler and ..eleganter etc.
      >>> On 04/06/13, Kerry McKenzie<kermck@...> wrote:
      >>> Guys
      >>> a rarely dumb question?
      >>> how hard is it to just get an old pc power supply AT or ATX ,.... who
      >>> cares either way,... you will get between 15 and 50 amps at 5 volts and
      >>> throw a couple of caps across it.
      >>> If you crow it,... it will be smooth
      >>> if you go to any computer repair shop they will possible give you as
      >>> many old ones as you want as most of them still work.
      >>> i have 4 or 5 in my workshop down stairs and use them for all sorts of
      >>> things and it so easy.
      >>> my 2 cents worth.....Kerry
      >>> PS Linux is still a bitch and I,m going nowhere with my projects ;-((
      >>> --
      >>> Kind Regards
      >>> Kerry McKenzie
      >>> PO Box 4492
      >>> Kirwan QLD 4817
      >>> Australia
      > yes, I agree...I use a vp-1020 satellite card in my computer and the P.S. noise is affecting the
      > sensitivity of the card....my ham antennas are more than 100 feet from the house due to the rf
      > racket produced by many switching power supplies in the house...even the darn router and cable modem
      > supplies were awful, so running as much as I can directly from my solar system 12v rail...but there
      > are just so many things nowadays that use these switching supplies it's hard to eliminate them
      > all...oh, and then there's a neighbors samsung plasma tv .. 300 feet away from here and it wipes out
      > my packet system when it's on...
      > grr...
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