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Re: [midatlanticretro] IMSAI to make the same music an Altair can?

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  • Dave McGuire
    ... It comes from just about everything, and the noise coming out of the radio is a blend of it all, including byproducts of constructive and destructive
    Message 1 of 1 , May 24, 2011
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      On 5/24/11 9:25 AM, B Degnan wrote:
      > I thought that the interference came from the front panel or the
      > processor cards, at least with the Altair anyway.

      It comes from just about everything, and the noise coming out of the
      radio is a blend of it all, including byproducts of constructive and
      destructive interference between RFI emitted by the various subsystems
      in the machine.

      In the common PDP-8/e music program, memory access patterns in
      particular are varied in software to produce the musical AM
      interference. This is because the interference generated by the
      magnetic core memory's X/Y drivers is strong enough to essentially drown
      out everything else. Those drivers push relatively large currents
      through the X/Y core select lines, at least compared to the signals
      flowing around in the rest of the system. (that's why core memory runs
      warm)

      Front panels also tend to be good emitters because the current
      required to drive those early LEDs, usually 10mA-25mA, is much higher
      than typical logic signals.

      -Dave

      --
      Dave McGuire
      Port Charlotte, FL
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