The latest propagation analysis for the best chance of Itasca hearing a "Strength 5" signal from NR16020 on 3105 kHz puts the airplane a whole lot farther away than 5 or 40 miles. At 40 nautical miles there was a 1% chance. At 60 nm there was a 5% chance. At 80 nm a 10% chance. Itasca had the best chance (50%) of hearing a Strength 5 signal if the airplane was between about 150 and 260 nautical miles away.
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Ric,
Bob wrote on the "3105 donut" thread:
"It's possible that there was direct path propagation at short distances, due to excitation of the airframe, but ICEPAC only calculates path loss for an ionospheric path. However, at 1,000 feet altitude (where Earhart said she was flying then), the horizon distance is about 38 miles. So outside about 40 miles, there wouldn't be any direct path, and skywave would govern. "
So I was asking him about the operation of the RDF within the 40 miles that
he said was possible with the direct wave, a signal that would be much stronger than the "near vertical incidence" skywave signals that create the donut. Those sky waves that create the donut travel at least 400 miles and suffer path losses one hundred times greater, 20 db, than the direct wave traveling only 40 miles. Plus, the signal strength of the signal emitted horizontally was much stronger, about 9 db, than at the takeoff angle of the skywaves that form the donut, according to Varney, so the direct signals would be about 29 db
stronger than the skywaves in the donut so should have been easily received.
So I am still curious what Bob thinks would be heard on the RDF.
gl