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Author Topic: New Post-Loss Radio Analysis  (Read 7235 times)

Jennifer Hubbard

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Re: New Post-Loss Radio Analysis
« Reply #30 on: August 05, 2018, 02:23:01 PM »

This is the quote that struck me most strongly:

"In a report written after the search for Earhart had failed, the commanding officer of the Coast Guard cutter Itasca categorically dismissed all of the reported post-loss signals."

We can see how things developed to keep AE and FN's fate so shrouded in mystery and doubt. By the time the islands were searched (flown over), Earhart's plane was not visible to the searchers. Therefore, they concluded she had not landed there. Therefore, if she had not landed, she must have crashed and sunk. Therefore, if she had crashed and sunk, the signals could not have been legitimate. It's a chain of logic resting on that first link of not finding the plane. If not for that first faulty link, these transmissions would have been taken more seriously long ago. The article lays out very well how the transmissions fit into all the other evidence, and why there is a problem with that first link in the chain.
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Ric Gillespie

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Re: New Post-Loss Radio Analysis
« Reply #31 on: August 05, 2018, 04:48:17 PM »

Well put Jenn.
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Ted G Campbell

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Re: New Post-Loss Radio Analysis
« Reply #32 on: August 05, 2018, 10:21:36 PM »

Thanks Ric.

What I am looking at, is there a correlation between the “harmonic” receptions and the Lockheed’s antennae propagation pattern.

So far, it seems odd that all the harmonic receptions (except Australia) fall in the Latitude range of 20 to 45 degrees N.  Australia is 30 degrees S.

If the antennae propagation pattern shows a stronger signal at a right angle to the island’s center line, I think there would be a strong argument supporting the hypothesis that AE did land on the island facing 317 degrees N , the only flat SW shore line.   Also, right engine would be up-shore.

Please provide the site’s location of the antennae details.

Ted Campbell
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Ric Gillespie

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Re: New Post-Loss Radio Analysis
« Reply #33 on: August 06, 2018, 06:42:11 AM »

So far, it seems odd that all the harmonic receptions (except Australia) fall in the Latitude range of 20 to 45 degrees N.

Where else could they fall?  That latitude range encompasses North America. That's where the English-speaking people with radios lived.

If the antennae propagation pattern shows a stronger signal at a right angle to the island’s center line, I think there would be a strong argument supporting the hypothesis that AE did land on the island facing 317 degrees N , the only flat SW shore line.

I don't understand how the island's geographic orientation could in any way effect the plane's radio transmissions.

   Also, right engine would be up-shore.

Why would that make any difference?

Please provide the site’s location of the antennae details.

There is no site with the antenna details. Bob Brandenburg created the propagation model for the plane's dorsal vee antenna in 2003.
« Last Edit: August 06, 2018, 06:45:55 AM by Ric Gillespie »
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Friend Weller

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Re: New Post-Loss Radio Analysis
« Reply #34 on: August 06, 2018, 08:13:12 AM »

I think Ted is asking if a contour profile has been created for the dorsal vee antenna on the Electra.  Bear with me on this for a moment....

Below are two screensnaps of antenna patterns.  The first is for a directional AM array.  It shows major lobes oriented to the north-east and to the south-west with a minor lobe to the north-west and relatively deep nulls separating the power lobes.  Without going into the details of how this array is fed, the orientation and spacing of the towers, the power ratios, and the phase angle, we can see there is pattern where receivers (which are not in the nearfield) distantly to the north-east and south-west would have a better chance of hearing that signal.  True, this is not the same as the Electra's setup but again, bear with me for just a little longer....

The second shows a non-directional contour for a low-power FM signal transmitting using a folded dipole antenna.  In theory omnidirectional, this signal is shaped by the terrain in the immediate vicinity.  This dipole is closer in construction to the Electra's antenna than a simple vertical radiator.  (And yes, Niku is essentially flat so there would be no terrain shaping of the signal.) 

Though neither of these examples are the same as the dorsal vee antenna on the Electra, I too wonder if the orientation of the aircraft would have any bearing on signal propagation and therefore, signal reception.   Given the "donut" in the signal contour which has been previously modeled, was there additionally any phase cancellation due to the off-center feed point of the antenna along with the characteristics of a vee antenna design which could have created a better chance of reception for those listening in certain directions from the aircraft? 

Might this have bearing on why the Itasca, though closer (yes - skywave versus ground wave, the harmonics of an unfiltered output circuit, etc.), could only hear a carrier at times while Betty and others heard much more?  I'm sure Bob Brandenburg could weigh in on this with much more detail.

(I hope I made sense....)
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« Last Edit: August 06, 2018, 08:20:02 AM by Friend Weller »
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Ric Gillespie

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Re: New Post-Loss Radio Analysis
« Reply #35 on: August 06, 2018, 10:08:36 AM »

I think Ted is asking if a contour profile has been created for the dorsal vee antenna on the Electra.

This is way beyond my pay grade but isn't that what I posted?
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Ric Gillespie

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Re: New Post-Loss Radio Analysis
« Reply #36 on: August 06, 2018, 12:16:39 PM »

Bob Brandenburg has provided the attached propagation models.

"Attached are 4NEC2 output plots showing the pattern for 3105, 6210, 15525, and 24840.  I can't find a plot for 12420 in my files, but that would be midway between 6210 and 15525.  The 3105 pattern is like a round apple, with the stem "dimple" at the top.  That general pattern continues as frequency increases, until at 24840, it gets "squashed" to one side.  The 6210 and 15525 plots show a vertical slice through the pattern, to show the interior. 

The "PB" suffix means the pattern was computed for phosphor-bronze wire, which was typically used for aircraft antennas.  Phosphor-bronze wire resistance is higher than copper, and the model takes the difference into account.   

The antenna patterns are oriented with respect to aircraft heading, i.e relative bearing 000 is dead ahead.  The model runs assume the plane was parked heading north."

 
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Ric Gillespie

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Re: New Post-Loss Radio Analysis
« Reply #37 on: August 06, 2018, 12:37:00 PM »

For those who prefer pictures to pdfs...

BTW, that "dimple" in the top of the 3105 pattern is what caused the "3205 Donut."
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Friend Weller

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Re: New Post-Loss Radio Analysis
« Reply #38 on: August 06, 2018, 01:39:03 PM »

Thanks Ric and Bob!  That answered my wonderings about the possibility of any directional wave propagation with regard to the dorsal vee antenna and the aircraft acting as the ground plane.  Being able to see the vertical component of the transmitted wave at 3105 (plus the harmonics) was helpful. 
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James Champion

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Re: New Post-Loss Radio Analysis
« Reply #39 on: August 06, 2018, 06:42:32 PM »

Quote
Bob Brandenburg created the propagation model for the plane's dorsal vee antenna in 2003.

The files indicate the V antenna was modeled with 4NEC2. This is a free antenna modeling program that models everything as 2D segments. Also, antenna modeling programs have come a long way since 2003.

4NEC2 can easily model a wire antenna, and that is what it is used for most. But I'm not sure how well it can model the curved metal structure of the aircraft, wings, and tail as more than a few 2D flat planes. I also believe it can't model the variable resistivity and height (tides) of the water under the aircraft. All of these factors may affect the antenna pattern.

Some quick inquiries on improved antenna modeling might be worth TIGHAR checking into.  Especially given the TIGHAR understand of the tides and the radio transmissions since 2003.
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Ric Gillespie

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Re: New Post-Loss Radio Analysis
« Reply #40 on: August 07, 2018, 06:54:40 AM »


4NEC2 can easily model a wire antenna, and that is what it is used for most. But I'm not sure how well it can model the curved metal structure of the aircraft, wings, and tail as more than a few 2D flat planes. I also believe it can't model the variable resistivity and height (tides) of the water under the aircraft. All of these factors may affect the antenna pattern.

Some quick inquiries on improved antenna modeling might be worth TIGHAR checking into.  Especially given the TIGHAR understand of the tides and the radio transmissions since 2003.

A quick online search doesn't turn up anything moire recent than 4NEC2.
Excerpting Bob Brandenburg from another discussion:
"4NEC2 is such a great tool -- it does the segmentation and field addition/subtraction. It's also important to carefully consider the effect of the antenna being close to ground  -- ground in this case being the fuselage.  The "2" in 4NEC2 means the second version of NEC.  The first version assumed the antenna was high enough that ground proximity was not a factor.  Version 2 considers the effect of the antenna being very close to ground.  BTW, there are two other versions: V3 which considers antennas lying on ground, and V4 which considers antenna buried in ground."
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Leon R White

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Re: New Post-Loss Radio Analysis
« Reply #41 on: August 30, 2018, 08:13:20 AM »

I just spotted this radio for sale.  I know nothing about vintage radios, despite the excellent education offered here.  BUT, if anyone were looking for such a thing, here is a 1937 Philco  that seems to have the correct bands:
https://reverb.com/item/827171-1937-philco-model-37620-tube-radio-1937-philco-model-37-620

Leon
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