Can someone please explain what "A peculiarity in the antenna’s transmission pattern" or what "propagation pattern of the aircraft’s transmitting antenna" means?

See links from article on--of all things!--"Radio propagation."

Thank you for the link.

That is interesting but it does not offer the fundamental questions regarding the "transmission patterns" or "propagation patterns".

**I remain skeptical of the doughnut hole propagation pattern theory**.

You should be skeptical, see: https://tighar.org/smf/index.php/topic,285.msg5763.html#msg5763

gl

Bob Brandenburg has not yet published his paper on the donut hole. I've kept him too busy working on underwater search technology.

The donut hole is the result of an anomaly in the propagation pattern created by the Electra's transmitting antenna. Bob discovered it when applying an updated and more precise version of ICEPAC (Ionospheric Communications Enhanced Profile Analysis & Circuit) to the computer wire grid antenna model. In explaining it to me, Bob wrote:

"Out to 80 nmi. the 50% and 90% probability signals from the wire grid version are about the same as in the previous model. That's because of the steepness of the radiation pattern "skirt" at low radiation angles, and the "dimple" at the center of the pattern -- it's similar to the dimple in the upper half of an apple. But at greater distances the wire grid signal strength is considerably higher because the "skirts" of the pattern are steeper than in the previous version -- in which the pattern begins to curve inward at lower radiation angles. The difference is analogous to the difference between an apple with more vertical sides -- like a Washington Delicious -- and one with more roundish sides, like a Macintosh. The new mean value rises above the threshold at about 150 nmi, and stays above until 280 nmi. The 10%, and lower, probability curves stay above the threshold all the way out to 340 nmi. So there was a 50% chance Itasca could have heard Amelia when she was about 140 nmi away, a 10% chance of hearing her at 80 nmi, a 5% chance of hearing her at 60 nmi, and a 1% chance of hearing her at 40 nmi.

It's doubtful she was within 40 nmi of Howland, since that would put her within visual range of Baker Island if she was on the LOP. As for the maximum likely distance, it was possible -- at 10% or less probability -- that Itasca could have heard her even as she laid eyes on Niku."

In case you missed it in all that, Itasca had the best chance of hearing Earhart when she was between 150 and 280 nautical miles away. Obviously, this is a huge game-changer in any speculation about where she was at the time of the last in-flight transmission heard by Itasca. It knocks the Crashed & Sankers calculations of where they should be searching for a sunken aircraft into a cocked hat. Millions of dollars utterly wasted - even if the Electra crashed & sank at sea. If the airplane was south of Howland on the LOP, it was probably much closer to Gardner than has previously been thought likely. That puts it on the reef at Gardner much earlier and with more fuel remaining than previously thought possible. That, in turn, influences the credibility of the post-loss radio signals which required power from batteries recharged by running an engine.

Once Bob has had a chance to get his paper written and published, any skeptic with the ability and inclination to buy the software and check his calculations will be able to do so. Replication of results is the essence of scientific investigation.