[TowerTalk] Cover antennas - the good news and the bad news

Jim Brown jim at audiosystemsgroup.com
Sat Oct 31 14:44:33 EDT 2020


On 10/31/2020 6:15 AM, jimlux wrote:
> This is a pretty standard technique these days - They use it for 
> calibrating radio telescope arrays, for instance.

Great tutorial, Jim! Two other important variables for earthbound 
antenna measurements are 1) terrain and 2) soil conductivity. You can't 
do this just anywhere. :) The N0AX/K7LXC test ranges were well chosen, 
but they tell us nothing about vertical pattern.

More than thirty years ago, thanks to greater computer power, those of 
us working in pro audio accomplished major advances in both acoustic 
measurement and acoustic modeling. One of the most powerful tools, and 
the earliest that got us all started, and the earliest, was Time Delay 
Spectrometry, invented by Richard Heyser, an engineer who worked at JPL 
on space communications. When he died early of cancer, he was President 
Elect of the Audio Engineering Society.

Computing power led to 3D modeling of loudspeaker systems in models of 
real acoustic spaces, taking into account the complex (mag, phase) 
response of speakers and arrays of speakers, over nine octaves, and 
computing responses over an audience. This required 3D measurement of 
loudspeakers in 5 degree increments of azimuth and elevation, and of the 
reflection/absorption properties of all of the surfaces in the acoustic 
model. Modeling had to take into account variations in the acoustic 
center of loudspeakers, and compute complex time response to every wall 
surface, and over audience areas. Once the model was complete, the 
response at any point could be convolved with a .WAV file of speech to 
assess speech intelligibility. All of this was well developed by the 
late '90s, and continued advancing thereafter.

Thanks to the broad frequency range of audio, and the extent to which 
reflections from room surfaces must be considered and added to compute 
both the responses and the room reverberant field, this modeling is 
several orders of magnitude more complex than what we're doing with 
antennas! Two of largest spaces I modeled at this degree of complexity 
were the Staple Center and the Nokia Center (now known as the 7,000-seat 
Microsoft Theater) nearby.

73, Jim K9YC



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