On 3/7/2011 7:04 PM, Jim Lux wrote:
tom wrote:


I have, at another amateur's station, on 432 MHz. Surprisingly the
speed came out almost dead on 300m/microsecond. Used .wav file
recording of transmit and echo and a good sound file editor with
sub-millisecond resolution when zoomed.


Surprisingly?

With implied facetiousness. Should have been more obvious I guess.

10m dish with full legal power, BTW. Very good signal to noise.

tom
K0TAR


You were thinking that propagation might be at some other rate?

the dominant error source in your measurement is probably the sound
card's clock.

For other fun measurements of em propagation speed.. melting the mode
pattern of a microwave oven cooking chamber at 2450 MHz into a single
layer of marshmallows on a plate (turning off the rotating turntable and
mode-stirrer, of course). Chocolate morsels might also work.


Other methods, for visible light, include the spinning toothed wheels of
Fizeau and rotating multifacet prisms of Foucault (later updated by
Michelson)

Interference fringes from a laser, as well.

if one is looking for more "radio" than "light".. look at the doppler
effect from a moving source. The fractional change in frequency is equal
to the velocity/propagation velocity.

If you do something like measure the frequency from, oh, an orbiting
satellite and get the whole "doppler curve" you can figure out the
frequency of the oscillator (it's the frequency at which the second
derivative of measured frequency goes through zero). You can measure the
velocity of the satellite optically (if you pick a satellite which is
visible, like ISS)