Topband: GAP Vertical Question

[Paul Christensen]

> First, they would be fools or have idiots for engineers to have more than 
> 120 radials. The only real reason they use 90 radials or so is it 
> sometimes gets them out of expensive proof-of-performance measurements.

Or, (1) to compensate for field degradation over the course of several 
decades.  In the case of WLS in Chicago, they laid 120 radials on top of an 
old set of 120 radials.  The base Z did not change, nor was it expected to. 
And (2), to better stabilize a pattern in the case of a DA where soil 
moisture/content changes with seasons.

> A typical half-wave BC tower is in the several hundred ohm range because 
> of tower thickness. They are almost never over 1000 ohms.

Right, typically a couple hundred ohms.  Modeling the base Z of a thick 
broadcast tower is very difficult with MoM software.  Changes in thickness 
can result in large base Z changes.

Paul, W9AC