[TangerineSDR] More tests with cars

David Waugh dwaugh at kent.edu
Sun Jul 4 18:25:04 EDT 2021


I ran some more tests to get a feeling for how far cars need to be from the magnetometer to not greatly influence the resulting data. The basic setup was running a tape measure down the length of the driveway and moving the car back and forth to different known distances from the front of the garage (using a cellphone to provide a timestamp of each move). The starting point (7.58 feet), was the closest point to the magnetometer, but in reality that was about 30 from the actual magnetometer location. The most distal location other than the street was 65 feet from the front of the garage door, but was actually about 58 feet from the magnetometer. Green dashed lines were adjusted (angled) to best match the levels present at each of the 5 times that the car returned to the origin (7.58 feet) during the test to account for the shifting field during the time the test was run (those times are labeled in green), the the line was moved down to the base line of the farthest distance which was the car parked on the street. Clearly there are a lot more sophisticated things that could be done with the numbers, but looking at the data it seems clear (somewhat) that at 56 feet (or 58 in actually distance from the magnetometer) there was minimal influence. At 50 feet from the garage door (the car is also about 50 feet from the magnetometer), the influence of the cars seems fairly minimal (especially in the Y and Z axis). At 65 feet from the garage door (about 60 from the magnetometer) the influence is almost gone. 



Below is a (more or less to scale) map of the location for the test described above, the test car was the only one present on the South side. Cars depicted are in approximately normal positions (cars in white space are those of neighbors). Blue circles are of a radius of 40 and 60 feet centered on the current magnetometer location. A further complication to my location is the road to the West which is on the property of a public school, and although unused on most times, is lined up (for maybe 45 minutes) with busses and cars dropping off and picking up kids for school. 






The map below shows a potentially better place to relocate the magnetometer, in the indicated position it would be at least 40 feet from any cars (but certainly not 60). The advantage to this new spot would be that cars will have less influence on the raw data, the downside could be that in the existing location, although our cars have a great influence, they are very obvious in the data and the location is far enough from the school road that cars and buses would likely have little influence (if I park my car on the school road I can’t see it in the data). If the school road was closer to the magnetometer, it might be harder to filter from the dataset because it would be a line of slowly moving cars and buses, not individual cars moving to and from fixed locations. 



Although I’m thinking about the best location for my magnetometer (and in general best locations for small lots), my question is really more general and for the actual end users of this data. How how much of an issue are cars on the data, and at what point does it become not worth it to collect the data in the first place?  Below is a graph from a “typical” day, you can see some cars come and go, but based on comparisons with NOAA data it seems capturing some real events.  -David KE8QEP




David A. Waugh, Ph.D.
Research Assistant
Department of Anatomy and Neurobiology
NEOMED
4209 State Route 44
Rootstown, OH 44272

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