"MICHEL SAMSON" wrote to "MIKE ROSS" (06 Jul 03  17:03:00)

 MS> I bet a good proportion of electronic hobyists can hardly miss
 MS> some story as that related to a worker who once left his chocolate bar
 MS> nearby as he fooled around an antenna.

I heard it as radar technicians during the WWII would leave their cup of
coffee on top of the output coil.


 MS> In any case, vapour, water or ice it all
 MS> impacts to some level.
 MS> I'm thinking of reception on a lake, for example.  So yes, i
 MS> agree.
 MS> :)

I acknowledge your agreement but I feel there are extra details which
need to be elaborated. Let's for a moment leave special weather events
aside and concentrate on the steady state average conditions. The radio
energy is transmitted as two components, a sky wave and a ground wave.
The sky wave will be quite attenuated at the line of sight limit but the
ground wave due to the nature of the Earth may be much stronger. So in
general at the line of sight limit it is the ground wave which is
generally the dominant signal. The power pumped into the ground wave at
the transmission station will depend on the radiation angle. The surface
of the Earth causes the energy to follow a curved path to some extent.
So at some angle the energy transmission will be greatest. What happens
in summer is that the radiation angle will raise somewhat so that less
energy is pumped into the ground wave. This increase in the angle is due
to vegetation, particularly foilage. Tests were done in pumping radio
energy through a forest and a difference of 6db was found to be absorbed
by the leaves in summer when compared to winter without leaves.


 MS> Fascinating describes the whole RF hobby only too well.

In my early studies I couldn't quite grok how an antenna really worked.
Sure there were explanations about energy fields and electrons but I
couldn't make the connection. One day it dawned on me that the antenna
is an electron accelerator and these can be coaxed to give off photons
when made to change directions. In fact this made me realize that
electicity isn't about electrons at all but rather the photons emitted
and received by them. In an electric current there is an electron flow
through the wire conductor but it is far from the speed of light. It is
the photon exchanges between electrons which travel at that speed.


 MR> Another intriguing comment about indoor antennas is that signal
 MR> strength inside a room may sometimes be stronger than outdoors
 MR> because of resonnant cavity effects of the metal structures...

 MS> Perhaps that applies to bridges as well and they would form
 MS> natural resonator networks with the surrounding buildings?!  Lets
 MS> imagine a sci- fi book starting from this one:  it was an unusually dry
 MS> night and a man who didn't suspect the cruel destiny he was about to
 MS> meet suddenly fried after he walked a last step, to the dismay of his
 MS> beloved wife and child who seen his fate sealed in a split second as
 MS> that of a moskito in a bug killer lantern, consequence of the most
 MS> unfortunate miscalculation ever!
 MS> :)

David Kronenberg here we come! Well, we are talking about amplifying
femto watts of radio energy, not exactly enough to fry our brains!

 Mike
 ****

... Help! I'm trapped at 0D1C:01DA.
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