Recent content by tech99

  1. tech99

    I Grating element of an acoustic grating

    I know the gratings work, and they were used for a large screen TV display in about 1939 in the form of the Jeffree Cell. However, it never occurred to me before that the grating effect must be pulsing on and off at acoustic frequency. With the Jeffree Cell I believe the cell used an acoustic...
  2. tech99

    This is why EM interference can be an issue...

    A CRT requires a line scan frequerency which is at about 16 kHz (625 system) and is delivered to the scan coils at around 25 Watts. Before the days when interfence from computers and broadband became so severe, line scan interference was very bad. It creates harmonics every 16 kHz right up the...
  3. tech99

    B Why can't two laser beams from two sources Interfere if they have a difference phase?

    Any two waves will interfere, but if they have different frequencies the interference pattern will be moving all the time, usualy too fast to see. It will repeat itself at the difference frequency. If, however, the frequencies are locked, then the inteference pattern will be stationary. If one...
  4. tech99

    Cheapest, easiest solar cell manufacturing methods on the Moon

    How will the Natural World of Earth, our precious biosphere, be saved by putting solar panels on the Moon?
  5. tech99

    Sea breeze and Chinese lantern question

    It might not be sea breeze as it could be the gradient wind. There is also variation of wind direction/speed with height.
  6. tech99

    Automotive Engine mechanisms during coasting (in drive mode) and engine braking

    I think it is a good idea for the drive train (and the driver) to keep the wheels connected to the engine when "coasting". In this way, the momentum of the rotating engine and flywheel wil make it less likely the road wheels cold stop turning or lock. In such a case, steering is impaired or lost.
  7. tech99

    Stargazing Possibility of detection of Earth approaching objects by gravity?

    The Arecibo radio telescope can obtain radar images of objects such as this which optical telesopes cannot see. In addition, the Sun is not a particularly strong noise source for radio waves.
  8. tech99

    I Can we connect two laser sources to make a stronger beam with a larger radius?

    Do we get speckles in the far field? Not sure.
  9. tech99

    I Can we connect two laser sources to make a stronger beam with a larger radius?

    If the lasers are side by side, we would see the "double slit" pattern superimposed on the spot. The two patterns multiply in terms of relative field strength. The problem is how to make a coaxial combiner with zero loss. Then the spot would be the same size as for one laser but double the...
  10. tech99

    I Can we connect two laser sources to make a stronger beam with a larger radius?

    It seems to me that if we place two lasers side by side, then at a great distance, greater than about diameter^2/(2*lambda), the beams will overlap. The spot will be the same size as for one laser, and the two beams, being incoherent, will add on a power basis, so the intensity of the spot will...
  11. tech99

    Accounting for mutual inductance in a Hartley Oscillator

    There are several ways of drawing a Hartley oscillator. The usual way I have seen is given like this and is a very convenient arrangement because no RFC is required, one side of the tuning capacitor is grounded (avoiding hand-capacitance) and no RFC is required. Of course, bias and decoupling...
  12. tech99

    I Strange approach to the line-fed slot antenna electromagnetic problem

    Sorry I can't do the maths, but I do know that the radiation from a slot is caused by the acceleration of charges in the metal. Wide slots and narrow slots radiate just the same. So the ground plane is the antenna.
  13. tech99

    I Why is the emissivity of metals low?

    I think Aluminium Oxide is a good dielectric and can support long waves efficiently but it has a crystalline structure which scatters waves with a wavelength comparable to the size of the crystals, such as light.
  14. tech99

    B Purely Capacitive AC Circuit -- Seeking intuition for why why voltage lags behind current

    A mechanical analogy is a spring. If we consider spring extension the analogue of charge, and force analogous to voltage, then extension is proportional to force, and Q is proportional to V. If you connect the spring to a rotating crank, so its length follows a sinusoidal pattern, then the force...
  15. tech99

    I Why is the emissivity of metals low?

    If the metal is polished, we can see that it creates an image of the source, which is a coherent secondary source and radiates almost as much power as it receives. If the surface is irregular, we see many secondary sources of radiation which are incoherent - they are of random phase. So the...