line-of-sight fallacy Re: [ASRG] The mistaken axioms of wireless-network research

[Bill N1VUX]

> At microwave frequencies, even 900 MHz, it is common to account for
> bending due to the atmosphere by assuming the Earth's radius is
> about 1.333 times bigger than it is geometrically.  

Yes, it's not a flat earth, it's a flatTER earth, R*4/3.

However, that varies with the weather.  At RF, the electrical dipole of the
water molecule makes it relevant to computation of the index of refraction ...
so the Relative Humidity and the layering in the atmosphere change
propagation.  Sometimes it so much higher (superrefractive) that the effective
Radius drops down to nominal or below, which can result in what we call
ducting -- repeated reflection off earth and refraction equivalent to
reflection off the moist layer. Sometimes it's subrefractive, which makes it
hard to hit what you normally hit. Superrefraction can interfere too, by 
bending a tight beam off target or by bringing in distant interference.

If the 2.7GHz Weather Radar is showing spurious echos from the land or even
sea ("Anomalous propagation"), there will be similar tropospheric range
enhancement for 2.4GHz WiFi etc.  For the next 5 days, according to my
interpretation of NWS weather model forecasts via Navy refractivity formulae,
conditions are favorable for a Pringles can in Scituate to hear WiFI nodes in
Provincetown on Cape Cod!

Cheers,

Bill
radio N1VUX