by Jim DeLoach, WU0I
Where should you point your Field Day antennas to maximize your Field Day score? In which directions exactly can be found the greatest concentration of other North American hams? And at what take-off angle?
To answer these questions, I found a database on the web with the home addresses of every ham in the U.S., and the home city of every ham in Canada. I geocoded these addresses to approximate positions -- based on zip codes in the US and cities in Canada -- then calculated the distribution by azimuth and distance from my Field Day QTH to all other North American hams. I then graphed this distribution, which visually conveys where all other North American hams are relative to me -- by azimuth and distance -- helping me to design my antennas.
Try this for yourself! Click on this link, where you can enter your Field Day latitude and longitude, and see the distribution by azimuth and distance from your QTH to all other North American hams!
Here's an example from my club's Field Day QTH in Northern California:
Here's how to interpret this plot. Azimuth and distance are broken in to 'bins'. Each bin represents a range of azimuth -- for example from 69 to 72 degrees, and a range of distance -- for example from 1,000 to 3,000 kilometers, and the value assigned to the bin is the percentage of North American hams who's home address falls within this azimuth range and this distance range from the Field Day QTH. Each bin is graphed in an axial plot, where the color of the trace captures the distance bin, and the point on the graph captures the azimuth and percentage. Visually, this conveys where the greatest number of hams are from the Field Day QTH, for each grouping of distance. Distance ranges are broken out in to separate traces on the graph, because the antenna needed to optimally communicate with a ham within 1,000 km is different then what is needed for a ham 3,000 km away or more.
This is of course an approximation. Many hams aren't at their home QTH for Field Day, so some error is introduced, but most don't wander too far. Also, not every ham participates in Field Day. Never the less, this presentation helps you visualize approximately where the rest of the North American ham population is relative to you, and in what concentrations -- which is not always obvious!
At my Field Day club we were really surprised by these findings. We knew the biggest population of North American hams would be somewhere to the East, but we didn't realize that so many lined up so tightly from 63 to 81 degrees. So we had our answer: point the beam to ~70 degrees, and don't bother with a rotor. These findings also told us that there are a lot more hams than we expected on the West Coast, within 1,000 km, so we should also deploy a high performance, bidirectional, high vertical takeoff antenna oriented for North-South propagation.
So give this tool a try, and maybe you too will find some surprises!
(c) Jim DeLoach, WU0I, 2017.