Recent content by jsg2021

  1. J

    LTSpice functionalities regarding its Frequency Domain Analysis

    SPICE doesn't use the SINE large signal in small signal - it uses the fact that with circuit analysis of a linear circuit, you can use Laplace forms for equivalent impedances so that: V = IR and V = I sL and V = I / sC. This means the small signal AC is just the same as a resistor linear...
  2. J

    AM, FM modulation, sidebands question

    Side bands can be understood from high school trig identities: When you modulate, you are using a multiplication operation implemented in analog circuitry. All "mixers" are essentially multipliers. That's why the symbol for a mixer is a circle with an inscribed "X". So say this involves a...
  3. J

    Maxwell 3D & Icepak thermal simulation for a air coil

    Honestly I wouldn't bother combining EM + Thermal for an air coil. Why? Because the conductive heat transfer of air of so starkly poor. Also "what frequency DC?" - 1 Hz could be sufficient to be DC; it's "on a spectrum" anyway. For microwave equipment, 50 MHz is "sufficiently DC"! Do a...
  4. J

    TV antenna dish: depth, f/D, or focal distance

    Rule of Thumb: a parabolic dish diameter should be 10x the longest wavelength. If you don't have that, you are better off using a different type of antenna.
  5. J

    Why are there chips in USB chargers?

    No. That's not what happens. READ the USB-3/USB-C charger standard! There is a negotiation to define who is the power source vs. power load, how much voltage and current can be supplied, etc. This is how these interfaces are able to charge devices faster than before. Either side can be the...
  6. J

    How much bulge means a bad cap?

    The "safe answer" is ANY bulge is a bad sign.
  7. J

    How to Convert dBV and dBA to dBW?

    Log10(x^N) = N * Log10(x) High school log identity. P = V^2 / R If you standardize the resistance/impedance, the R falls away and it's P ~ V^2 vs. V which with log10 gives a factor of 2.
  8. J

    Why Does Power Cycling Cause Test Equipment Failures?

    There's no reason why it should have equipment problems either from being left on 24x7 or having power cycled. Test equipment is designed for this. However there are contributors specific to relay testing and test equipment that themselves use internal relays: Relay coils can create large...
  9. J

    Why are touchscreens becoming popular in test equipment (scopes, etc)?

    The very same reason that iPhones replaced push-button mobile phones: the design and support results in more programmable, more useable, more updatable and overall cheaper to make things when using touch-screens replacing buttons. Literally controls become software instead of hardware which...
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