jfinch:
proposed location for placing the data points
The one point that might need explaining is where to pick the two points for the distance measurement. You want to pick an approaching point where the plane is about 45 degrees from the horizon and then a leaving point at about the same angle. I try to pick the point just before the curve really starts to go vertical. You don't have to be exact, just enter the frequency and time (in milliseconds) and the spreadsheet will do the rest.
The S curve is kind of wide (spread out) at these locations. It might seem intuitive to pick a point in the "middle" of the spectrum, but I propose that the proper point to pick is on the underside of the S curve. Here's my reasoning... I think the spread out nature of the spectrum is due to the microphone "remembering" what it was picking up a millisecond ago (hysteresis). If that's the case then I think the lowest frequencies will match closest to actual (the spread upward is the hysteresis effect).
http://www.rcgroups.com/forums/showpost.php?p=6531167&postcount=20
Taking his explanation and advice per Chris's recommendation of use I get the following: Thank you Chris! Now go build a TD .010 racer your on the list 
Last edited by Pond Skipper; 03-25-2016 at 06:04 AM.