RE: Why Lower Power?

[Peter Murray <pete@partnercomm.com>]

Additional bays on the transmitter array will effect higher gain - a 
flatter pattern (in the vertical plane) that will focus power towards the 
horizon. This "effectively" _increases_ the ERP of the station. The actual 
power coming out of the transmitter and the gain of the antenna combine to 
form the ERP, and that's the figure that makes a station "50KW".

This leads me to ask the following question:
Certainly, if all things are equal, then running a high-gain array and 
lower power is the same as running a low-gain array and far higher power. 

I know all things aren't equal.

What is the tradeoff with when one selects a very high gain array? More 
pronounced shadowing? Less of a diffractive effect? I'm assuming there is 
a sweet spot of efficiency, where you get to trade the $40K/mo power bill 
for higher gain, but once you go above a certain point, the returns begin 
to diminish... 

I'm expecting this applies even in arrays where the focus of the gain is 
not in the plane perpendicular to the axis of the array, but down a few 
degrees, to account for that pesky planetary curvature....

-Peter Murray (N3IXY)
Pittsburgh, PA