[TowerTalk] Fwd: Change in Frequency As Antenna Height

[Jim Brown]

On Thu,6/2/2016 10:08 AM, Jim Thomson wrote:
> But I dont know if scaling or extrapolating the 10M data is valid.

Gee, we've only been building and testing scaled models to help us 
understand and predict complex systems for 100 years, in fields I'm 
familiar with as widely varied as antennas and room acoustics. Maybe YOU 
don't know, but those who have taken the time to study do.

The degree to which scaling works depends strongly on how elements of 
the model accurately describe conditions at the scaled frequency -- in 
room acoustics, it's things like the reflections and diffusion 
characteristics of the wall materials, the attenuation of air, etc.; 
with this particular antenna example, it's the difference between how 
soil acts at 7 MHz as compared to at 30 MHz, and the diameter of the 
antenna conductors as a fraction of a wavelength.

BTW -- there are other parallels of folks using a single (and often 
inappropriate) variable to describe a system. With acoustics, it's 
Reverb Time, RT60, the time it takes sound to decay by 60 dB in a closed 
space; with audio, it's "frequency response," with cars it's "zero to 
60," and with antennas, it's SWR. Paraphrasing the late Dick Heyser 
(another JPL scientist whose hobby was audio and who revolutionized 
audio with his teaching and his invention of Time Delay Spectrometry), 
"trying to describe the performance of an audio system using only its 
frequency response is like trying to write poetry with only one word in 
your vocabulary."

73, Jim K9YC