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Author Topic: Discussions Re Radio Bearings, Fall 2012  (Read 29800 times)

Gary LaPook

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #15 on: September 04, 2012, 04:44:32 AM »

I'm a little surprised that the Howland bearings pdf of ten charts has only been downloaded four times since the other documants have been downloaded many more times. The Howland bearings charts are the most important things to look at. As an example I am attaching four of them as jpegs. The first shows the SSE line and the correct 167° line; the second, the total area covered near Gardner; the third the area covered south of Howland and the last the area to the north with the uncertainty area of the Midway bearing showing the overlap of these two areas.

gl

https://tighar.org/smf/index.php?action=dlattach;topic=940.0;attach=4164

Gary, when I first looked at this post, I thought that the PDF lines were only the reference to the pictures and didn't click on them thinking I would only see the picture again as in some previous posts. Others may have done the same since they are right next to the pictures.

Does this not help illustrate my "not 100% idiot proof" comment? ???
I thought that that might be the answer, it is an easy mistake to make. Next time I will try placing links to pdfs after all of the jpgs instead before them. I am going to go back and see if I can modify that.
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O.K. that worked, now the link to the charts is at the bottom of the list, much better.

gl
« Last Edit: September 04, 2012, 04:01:59 PM by Gary LaPook »
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C.W. Herndon

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #16 on: September 04, 2012, 04:51:11 AM »

I thought that that might be the answer, it is an easy mistake to make. Next time I will try placing links to pdfs after all of the jpegs instead before them. I am going to go back and see if I can modify that.

gl

Well, it was the answer for me anyway. Guess I must be one of those "idiots". ::)

Glad I might have helped a little.
Woody (former 3316R)
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C.W. Herndon

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #17 on: September 04, 2012, 04:55:15 AM »

-------------------------------------------------------
O.K. that worked, not the link to the charts is at the bottom of the list, much better.

gl

That is much better. Thanks!
Woody (former 3316R)
"the watcher"
 
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Alan Harris

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #18 on: September 05, 2012, 04:45:30 PM »

O.K. that worked, now the link to the charts is at the bottom of the list, much better.

Despite increased viewing of Gary's work (IMO very informative), this topic appears to be dying on the vine . . . wonder if it's a general lack of interest, no one else has anything specific to offer, or just that few people are even finding it?
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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #19 on: September 19, 2012, 03:50:05 PM »

I am starting this topic for discussion of recent points raised in other threads possibly affecting the Radio Direction Finder Analysis and, marginally, the Post-Loss Radio Signals analysis.  Most of the points arose in the Lambrecht Search topic for reasons not germane here.
<...>
3)  In recent posts Art Johnson has offered information as to the crossing of bearings, and as to the customary practice of adding bands of increasing uncertainty with distance instead of merely drawing single lines.  This information is quite clear, and it seems there is opportunity to make a different chart showing area intersections rather than line crossings. However (and here I venture "Where There Be Serpents" as far as my own knowledge goes) I believe the "standard" uncertainty would apply generally to well-received signals that persist long enough to get "good" fixes, and may not be the whole story?  Some of the earlier Research Papers and other TIGHAR material suggest that for very weak and/or fluctuating signals there are other possible effects (atmospheric, etc.) that could shift a bearing by larger amounts, even tens of degrees.  OK, I will shut up now, as I'm well past my limits.

Have at it if you will, people!

Allan,

Gary LaPook has uploaded a chart to another thread using his estimates of possible bearing accuracy range:

http://tighar.org/smf/index.php?action=dlattach;topic=944.0;attach=4235

I cropped his chart to show what I was speaking of:
 (You could just expand Gary's chart to 200% and scroll down to the intersections.)
Quote
If I were drawing a chart for navigation, it would just project the lines from the locations for Oahu, Midway and Wake. It would just cover the area around the crossings...

What you have now is a pentagon with boundary 1. being the short piece of green line crossing in the Baker island area.
Boundary 2. (going clockwise) would be the yellow line from Howland that passes NE of Gardner and Tokelau.
Boundary 3. would be the green line passing SE of Tokelau.
Boundary 4. would be the purple line (from Wake) that goes off the bottom of that chart. 
Boundary 5. is the yellow line (from Howland) between the purple 4. and green 1.

Now you have the five sided (pentagon) area that is about five to six hundred miles wide in the area of Tokelau and perhaps eleven to twelve hundred miles tall (down to the 'off the bottom of the chart' intersection of purple 4. and green 3) and you would place greater weight to the middle of this shape.

If you accept the hypothesis that they began to follow their 'LOP' of 157° down from the area of Howland Island, you would also have to place a limit on that eleven hundred mile vertical dimension of the pentagon by the fuel they had available.  Meaning that even Tokelau Island might have been beyond their maximum possible range.  Tuvalu Island would be outside that pentagon and since the Radio use depends on dry land, this limits your search to islands within your pentagon.

Gary's estimate of bearing +/- error is no doubt a lot closer than my inital +/- 1° taken from a 1936 Report that no doubt depended upon perfect conditions.  (The example given resulted in excess of 20° error when combined with their faulty compass.)

It has been my practical experience that bearings were usually within 1° and less often +/- 3° or more, but this is based on using relatively modern airborne equipment, not ancient ground based HF/DF equipment. 

I will accept Gary's estimates of Bearing errors (+/- 10° from Hawaii & Wake; (+/- 21.25°) from Howland) for the conditions existing at the time even considering that as a dedicated Crashed n'Sunker he is of the opinion that NO Post-Loss Radio signals at all could be possible.
Art Johnson
 
« Last Edit: September 19, 2012, 04:26:48 PM by pilotart »
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Mark Pearce

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #20 on: September 19, 2012, 04:22:19 PM »


"...It has been my practical experience that bearings were usually within 1° and less often +/- 3° or more, but this is based on using relatively modern airborne equipment, not ancient ground based HF/DF equipment." 


Randall Jacobson made some interesting comments on the topic of '1937' bearings and accuracy-

http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Itascasearch.html 

"... [On July 6th] Itasca asked Howland to take a bearing on it at 0800 GMT. At 0832 GMT, Howland reported that the bearing was NNW or SSE, taken with a magnetic pocket compass. The Itasca at this time was 342.2° relative to Howland (magnetic), a good match to the 337 degrees reported. At 0930 GMT, Howland took another bearing, observing NW (315 degrees), versus the 345.9 magnetic orientation to Itasca, a far worse bearing error of nearly 31 degrees. At 0947 GMT, PAA Honolulu reported a bearing on the Itasca of 196.5°, but the bearing to the Itasca is really 232.38°, an error of nearly 36o! Based upon these errors obtained over the past couple of days, direction bearings should be considered indicators of direction, and not treated as literal bearings with any accuracy."


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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #21 on: September 19, 2012, 04:57:46 PM »

Mark,

Yes, that PAA Honolulu bearing was Bearing 8 on the RDF Analysis and analyzed on page six of the 8 page Brandenburg RDF Report completed six years ago.  It would be worthwhile to read the entire report, but page six will give you Bob Brandenburg's Expert Analysis of Bearing 8, I certainly don't have that particular expertise, so I just accept what Bob has written.  Page three will explain the terrain he is referring to.  My memory of Mokapu was the largest group of feral cats I've ever seen, and a really spectacular view to the east and south.

That excessively large set of errors that led to the loss of the Croydon was caused by a faulty HF/DF Station that was on schedule for replacement along with an excessive sunrise error compounded by a faulty compass on board the Croydon Aircraft.

The 20 - 45 degree wide projection areas using Gary's error predictions are in my opinion also "indicators of direction", and not to be "treated as literal bearings with any accuracy."
Art Johnson
 
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Alan Harris

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #22 on: September 19, 2012, 04:59:27 PM »

I am glad to see some interest returning to this thread!

Art, thanks for that.  I was, and still am, interested in what other members might think about Gary's post relative to possible errors.  Also of interest to me in the "area chart" is the effect, or lack of it, of the Midway bearing recently declared Not Credible.  What I mean is, that Midway is/was not a big determinant of the intersection area, so removing it causes little change; except of course that it eliminates one "confirmation".

Mark, thanks for that also.  Although I find it kind of generally scary in terms of what do we really know, lol.  The 947 GMT bearing test has come up before, but I was not personally aware of the others.  Certainly I am not equipped to argue or otherwise comment on any of Jacobson's work.
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Gary LaPook

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #23 on: September 19, 2012, 08:38:21 PM »

Mark,

Yes, that PAA Honolulu bearing was Bearing 8 on the RDF Analysis and analyzed on page six of the 8 page Brandenburg RDF Report completed six years ago.  It would be worthwhile to read the entire report, but page six will give you Bob Brandenburg's Expert Analysis of Bearing 8, I certainly don't have that particular expertise, so I just accept what Bob has written.  Page three will explain the terrain he is referring to.  My memory of Mokapu was the largest group of feral cats I've ever seen, and a really spectacular view to the east and south.

That excessively large set of errors that led to the loss of the Croydon was caused by a faulty HF/DF Station that was on schedule for replacement along with an excessive sunrise error compounded by a faulty compass on board the Croydon Aircraft.

The 20 - 45 degree wide projection areas using Gary's error predictions are in my opinion also "indicators of direction", and not to be "treated as literal bearings with any accuracy."
But remember, it is NOT my estimate of bearing error, it is the U.S. government's experts' estimate of bearing errors as published in Radio Navigational Aids, Publication 117. The +/- ten degrees is for a weak signal at 150 NM. For a "scarcely perceptible" signal it can exceed ten degrees even at only 150 NM. At any distance greater than 150 NM the errors also increase.

gl
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