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Author Topic: Discussions Re Radio Bearings, Fall 2012  (Read 29858 times)

Alan Harris

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Discussions Re Radio Bearings, Fall 2012
« on: September 02, 2012, 05:53:52 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.

Let me begin by saying that I am not an expert here, in fact roughly the opposite.  What I know in total about the physics of radio wave propagation, the state of RF Engineering in the 1930's, and the operational practices for obtaining radio bearings would not be "acne on the posteriors" of members such as Chuck Varney, Bob Brandenburg, Gary LaPook, and Art Johnson.  I got into this merely by asking a couple of simple-minded questions; it is my hope that some informed people will chime in and continue the discussion.  If I am lucky enough for that to be the case, I will just sit back and read, and never have to post here again, lol.

The points possibly deserving further discussion include:

1)  The Radio Bearing 5 signal (Pan Am, Midway) has been classified as Not Credible, for what appear to be good reasons, namely, length of the transmission and the very strong language in the Midway operators' description (". . . proved to be . . . later definitely discarded . . .").  Does that mean our standard reference RDF Analysis bearing chart and discussion (linked above) should be modified sometime to reflect the change in evaluation of Bearing 5?

2)  I have asked the question whether the evaluation of Radio Bearing 6 (Howland Island experimental RDF) should also be re-examined.  It occurred on the same day, at the same time, and on the same frequency as Bearing 5, and so could potentially be reception by another station of the same signal as Bearing 5, now classified Not Credible.  Or to ask it another way, can we determine whether or not Bearing 6 reports the same signal as Bearing 5?  Differences in perceived signal strength and duration could be explained both by different receiving locations and by the reported possible malfunction of the Howland unit due to operator abuse.

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!
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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #1 on: September 02, 2012, 07:08:48 PM »

. . . I went back, rewrote and added a paragraph to my original explanation to try and make it more understandable for you and everyone reading this FAQ.
Quote
At some point do we also need a "re-do" on the bearings charts to remove Bearing 5 (Midway), which was classified as Not Credible a couple days ago?

Also I then asked a question about Bearing 6 (Howland), whether it should be re-evaluated because possibly another hearing of that same signal.  My question sort of died on the vine because immediately followed by much more interesting posts about how to cut aluminum at home for fun and profit . . .   :)

(Yes, more thread drift, administrators feel free to move this, or tell me to move it somewhere.)

Alan,

You could certainly remove the Midway and Howland (if they are not credible) Bearings from the chart.  That still leaves Oahu and Wake to provide crossing bearings.

I had stated that a single bearing was just one 'LOP' and you could be 'anywhere' along that line (thin wedge actually).  However if that line crosses land (islands) and you are positive that the transmitter must be on land, then the island/islands provide the 'crossing' LOP for you.

I did not read the report that eliminated Midway, but recall that it might have been because the 'carrier' went on for two hours and that did not seem possible.

I don't know if that was impossible from equipment standpoint or not.

If it was just what Gary said about "too long to hold the PTT down"< i wouldn't necessarily buy that.  It would depend on the gas supply, but I could envision cranking the engine on a falling tide, placing a strap around that PTT and babble away, or perhaps just go off to explore the Norwich City while the Electra put out a continuous carrier signal for the new (since 1932) HF/DF stations to track and plot...  She would have needed to return and stop the transmission for an hour of battery charging before rising tide shut-down, but plenty of time for that scenario.

There were anecdotal reports that sounded like Betty's description of hearing something like an 'open-mike' conversation between a man and a woman, you usually only hear one voice on a standard 'noise-cancelling' mike if it is held close to the lips as it should be while transmitting in flight.

______________________________________________________
This post was moved from the topic "Re: FAQ: Colorado / Lambrecht Search, 9 July 1937" at Allen's request.

I will also copy some of my other posts from that thread on this subject to this new thread and so they will be 'out of chronological order'

Also, Gary LaPook and Chuck Varney have a lot of good posts in that previous topic on this subject.

Also John Guthrie Ford and Ric Gillespie
Art Johnson
 
« Last Edit: September 02, 2012, 07:58:28 PM by pilotart »
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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #2 on: September 02, 2012, 07:26:52 PM »

Archaeology is a field in which the practitioner is a slave to the vagaries of preservation, i.e. what someone in the dim past might have accidently left for us to find. Accordingly archaeologists tend to take a rather narrow view of what exactly we can deduce from artifacts - this is even more so in problems where there is no other information e.g. written sources, and the only source of information is an artifact. The artifact then becomes the focus of our thoughts and conclusions. If it is associated with something that can be clearly understood, or a clear association that enables us to tie it precisely to an event then that's wonderful. However most of the time not only don't they have these characteristics but even the event is a complete mystery - therefore we hypothesize a lot and speak with certainty on precious few occasions. That is why I will always err on the side of caution when interpreting any artifact - even if the possibilities look attractive, honesty compels one to say "yes that is possible but so are a number of other interpretations and accordingly we need more evidence to narrow those options". That isn't negativity that is simple caution and surrender to the prayer that is uttered by all human beings, whatever their beliefs, "oh please don't let me get egg on my face":)

I 'll leave you to reread my comments about Betty's Notebook and also those of others. You are entitled to your interpretation but also I am entitled as are others to our doubts. The post-loss radio messages are also not so clear cut in their transmittal location as you would think so I can only respectfully suggest that you have another look at the map on which they are charted.

Regards

Malcolm

Thank you for this explanation of your caution with artifacts.  It is certainly a first-class mystery that TIGHAR is dealing with.

I presume this is the Post-Loss Radio Bearing chart we are discussing:

Five of the seven Bearings plotted cross closest to Gardner or McKean.

The not plotted bearing of 213 degrees (1523Z to 1530Z July 4th) reported by Mokapu Point, Oahu also passes within 30 nmi southeast of Gardner Island, which makes it six of the eight.

This report discusses each of the eight Bearings and concludes with:
Quote
The evidence associated with Bearings 2, 3, and 7 strongly supports the TIGHAR hypothesis that Earhart landed at Gardner Island and transmitted radio signals from there. The evidence associated with Bearings 1, 4, and 6 moderately supports the hypothesis, and the evidence associated with bearings 5 and 8 is inconclusive.

In sum, the weight of available evidence strongly supports the TIGHAR hypothesis.

I would most certainly agree that you are entitled (as are others) to your doubts.

I will never believe that Betty fabricated or misrepresented her Notebook and do believe her testimony about the involvement with her Family and Neighbors in the event.  This would disavow her getting that information from any "March of Time" or other sort of local broadcast. 

BY FAR the greatest significance of the "Betty Notebook" to me is that it was not until after Betty appeared, that TIGHAR researched ANY Post-Loss Radio Report.
Art Johnson
 
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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #3 on: September 02, 2012, 07:42:35 PM »


See Lambrecht's letter in which he discusses the planning for the search, no mention of radio bearing as affecting that planning. Lambrecht said exactly wht Fiedell said about this planning so I don't understand your comment about sweeping the bearings under the rug.

gl

I must admit I am puzzled as to why any one would claim that the Navy swept the post loss messages under the rug. Perhaps the Navy evaluated them, took note of the different transmission times, and wisely concluded that as they were not synchronous then they couldn't cross near Gardner - or anywhere. I note from the chart that shows them that where they cross is actually in the ocean, apart from one which can be extended to Gardner but could also be on a line traversing open sea (which makes the Electra as the source impossible). There is so much background noise and static regarding these messages, and I don't mean that just in the radio sense, that they are very difficult evidence to properly assess - they offer a veritable cottage industry of theories on their own.

Then we come right back squarely to the real problem which is the Navy despite the faults assigned to them by the wisdom of hindsight did actually search Gardner and didn't see anything apart from the rather ambiguous comment by Lambrecht of "recent habitation" but people tend to ignore that a term like "recent" is ambiguous unless it is qualified by saying how recent. Apart from the great big shipwreck on the reef, this could also refer to visible remains of the buildings from the Arundel period or even traces left by the Norwich City survivors, but even more importantly there was no Electra and certainly no sign of Earhart and Noonan. Who I would think it should be clear to everyone given Gary's explanation of survival chances (with which I agree) would, if they were on the island, be still ambulatory and not starving and collapsed comatose under a tree. Gardner may have not been quite the tropical paradise of the tourist brochures but it had food and it had water albeit brackish or obtainable.

Malcom,

You may of noticed that I had posted: "...perhaps it would be better (for me) to just say that the radio calls were ignored after their search had been completed." as I should not use unkind metaphors in reference to fine people who were doing the best they could and I can't blame them for not mentioning Post Loss Radio after their search was complete.  I would edit my original statement, but as you know 'once you put something online, it's forever there' (at least ;D in post 'quotes').  Let me state that I have nothing but respect for those people and what they tried to do.

Your statement:  "Perhaps the Navy evaluated them, took note of the different transmission times, and wisely concluded that as they were not synchronous then they couldn't cross near Gardner - or anywhere." shows a lack of understanding of radio bearings.

It is true that if you are locating a moving target, the times must be synchronous, but in locating a fixed target the times or days of the Bearings do not affect the accuracy.  In fact it allows for greater precision when you are plotting a stationary target.
 
The Bearing Chart simplifies the accuracy of those radio bearings and actually show a more precise assignment of Gardner Island that would be possible in my opinion.

Radio bearings were not that precise and at that time period were probably +/- one degree of accuracy or one mile left or right for each sixty miles from the station.  That would mean that those lines would be 1800/60=30 miles either side of center or a possible span of 60 miles.  This would make each line look as wide as the two bearings from Oahu that show 213/215.

The only area of importance is in the area of crossing, those lines that have no 'crossings' are just single LOP's and you can't determine position.  (Read the analysis if you want an explanation if those.)

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 and those 'lines' from the bearings would be about 60 miles wide (assuming about 1800 miles from the bearings centers).

Of course we also have that bearing from Howland experimental HF/DF at a width of about 12 miles.  This one was plotted from a pocket compass which was why it was drawn as "NNW/SSE".

With this you would end up with a hexagon about 100 miles across approximately centered on Gardner and the Howland bearing would only add precision.  My 'one' degree came from a 1936 estimate of HF/DF Ground Station Accuracy, no matter the "degree of accuracy" (you could even assign a different "degree of accuracy" for each specific Bearing depending upon confidence) that you wish to apply, it will still center in the same location, just grow in size.

Just as when you cross LOP's from celestial points, your location is considered to be somewhere within this hexagon (or quadrilateral when you only have two bearings) and you place more confidence in the center of the area.

(This post was moved from another topic and Malcom had replied to the above information as you see below and I replied to him with this further information):

It is true that if you are locating a moving target, the times must be synchronous, but in locating a fixed target the times or days of the Bearings do not affect the accuracy.  In fact it allows for greater precision when you are plotting a stationary target.
 


Thank you Art for that reply. The problem as I see it is that the post loss radio messages have to be assumed to be stationary in order to accept that they come from Earhart, obviously they cannot be moving if they are out of fuel and therefore must be in one spot. But, and this where we come back to the nub of the problem, the messages really aren't precisely centered on Gardner are they and the Navy did fly over the island and apart from the report of "recent habitation" signs which is a relative term in any case they neither see any people nor an aircraft. So are they really stationary, and how accurate are the bearings - frankly to me those bearings are a bit splayed.
it is obvious that you still do not understand Radio Bearings.

Yes those bearings over two days would indicate a stationary transmitter, that 'splay' is due to that +/- factor of the Bearing's accuracy confidence and the actual location is just 'somewhere' within that 'box' computed from the crossing bearings adjusted for their +/- estimate and distance. 

We do know that the Electra Must have been on dry land, so that still limits your search to just a few islands.  The Navy initially encompassed all of the Phoenix Islands and that would have been their 'safe' estimate of the Bearing's accuracy.
__________________________________
Now with a disclaimer, I am going to delve into a little bit of 'coulda'-'shoulda' that has no effect on the outcome, because it was never acted upon:

From An Answering Wave: Why the Navy Didn’t Find Amelia

Rear Admiral Orin G. Murfin asked the Navy Department that he be permitted to divert the battleship U.S.S. Colorado and it was 2:08 PM on July 3rd before she cleared Pearl Harbor.  By now Murfin was aware that there was a fast ship with an aircraft aboard far closer to the search area and in receipt of radio signals at 7 PM on July 2nd (or 0600Z July 3rd) believed to be distress calls from Earhart. She was the British cruiser HMS Achilles (later to win fame in the pursuit of the Graf Spee). On July 3rd Achilles was 800 nm east of the island group Colorado would eventually search on July 9th. Unlike Colorado, she was familiar with the area and could have had her Supermarine Walrus observation plane overhead the suspect islands fully four days before they were, in fact, searched. No request was made for her assistance. Instead, the aircraft carrier U.S.S. Lexington, preparing for Fourth of July celebrations at Santa Barbara, California, was ordered to rendezvous with four destroyers and proceed immediately to join the search, refueling in Hawaii on the way. But first she had to re-provision at Long Beach and then go to San Diego to take on aircraft whose pilots had to be recalled from holiday leave. It was July 5 before the Lexington Group began its 4,000 nm voyage to join the search.

It had seemed to me that a request would have been in order, considering the circumstances.  It seems that Political Concerns (USA vs British Empire relations in 1937 in the Pacific) trumped logic.  I would have thought that Admiral Murfin would have had the authority to make the request, you must know that Roosevelt would have approved...
_______________________________________________
Just to show how TIGHAR continues research and modifies and improves their hypothesis; the Achilles reception event was rejected in October 2000 as "not credible".  Then in a more recent study using 21st Century expertise, the same message is now considered credible.

Malcom, I am aware that we have agreed to different opinions on validity of radio messages and am aware that not all 'experts' will agree on the Post Loss Radio subject.

I do feel a need to correct an obvious misunderstanding when it falls within an area that I am qualified to comment on.
____________________________________________________________

There is no doubt that the contributions of the members who intelligently and constructively disagree with TIGHAR are what makes this public forum worthwhile and if it were only agreeing members, it might not accomplish nearly as much.
Art Johnson
 
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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #4 on: September 02, 2012, 08:01:57 PM »

I received a correction from Chuck Varney dealing with my post containing the graphic of the Bearing Chart and this was my reply:

Five of the seven Bearings plotted cross closest to Gardner or McKean.  The not plotted bearing of 213 degrees (1523Z to 1530Z July 4th) reported by Mokapu Point, Oahu also passes within 30 nmi southeast of Gardner Island, which makes it six of the eight.

Art,

I think you’ll find that your “not plotted bearing” is indeed plotted; it’s just time-tagged 1515Z rather than 1523Z-1530Z.

The bearing that is actually not plotted, bearing 8, may provide an indication of how good some of the others were. This bearing was taken by Mokapu on 6 July at approximately 0947Z. It resulted from a scheduled attempt to take a bearing on Itasca, a target at a knowable location on a known frequency, 3105 kHz. The bearing obtained (197°) was 35° from Itasca’s true bearing (232°) at the time.

A problem with bearings plotted on a map is that they give the illusion of certainty where there may have been none. For example, referring to the subject map:
 
The solid black line from Oahu labeled 213° doesn’t tell you: rough bearing only, weak and swinging signal, frequency not accurately determined.
 
The solid black line from Oahu labeled 215° doesn’t tell you: close to 3105 but so weak couldn’t get a fair check; very doubtful bearing.

The solid black line from Midway labeled 175° doesn’t give you Midway’s assessment: proved to be some unidentified station probably in South America or Russia and was later definitely discarded as a possibility [of being KHAQQ].
 
The solid black line from Howland labeled NNW/SSE doesn’t tell you: weak carrier, no call given, bearing only approximate, frequency slightly above 3105.

The solid black line from Wake labeled 144° doesn’t tell you: very unsteady voice modulated carrier [or that the signal was unreadable, that no callsign was heard, but the operator was nevertheless positive it was KHAQQ.]

Chuck

Thank you Chuck,

You are correct, I had counted seven lines on the chart and knew they were talking about eight, I did not catch that it was #8 that was not plotted because it did not talk about a bearing to KHAQQ.

I do hope that you noticed that in addition to a link at the top to the source of that chart, that I had also provided a link below "This report discusses each of the eight Bearings" and that report with several pages on each bearing discusses all of the problems you have posted and more.

Over 50 pages in that report and I advise anyone with an interest to spend some time to read it.  I see that Gary has a link to a different report and perhaps it is a simplified version of the same as it is only 10 pages.

That report also has a lot of positive things to say and it seems that those weak, wobbley transmissions from Gardner fit the scenario better than any other source.
Art Johnson
 
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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #5 on: September 02, 2012, 08:10:52 PM »

This was my second post in response to Chuck after he responded back.

I do hope that you noticed that in addition to a link at the top to the source of that chart, that I had also provided a link below "This report discusses each of the eight Bearings" and that report with several pages on each bearing discusses all of the problems you have posted and more.

Over 50 pages in that report and I advise anyone with an interest to spend some time to read it.  I see that Gary has a link to a different report and perhaps it is a simplified version of the same as it is only 10 pages.

Art,

Yes, I did take note of your link.

If you go to the beginning of the RDF report version that Gary linked and compare the report in its entirety to the version that you linked, you’ll find them to be effectively identical in length and content.

One point of my last post was that if one has source material at hand—whether it’s for lines drawn on a map or for assessing someone else’s conclusions—it’s a good idea to read the source material before drawing your own conclusions about meaning or content.

BTW, additional RDF-related material is accessible from these links:
   DF site tables
   Pan Am Memos

Chuck

Chuck,

Thank you for your response and your links to further information.

It had been after my last post that I read Gary LaPook's link and of course soon realized that way beyond just the ten pages I had first glanced at, that it contained links within to seven more sections.  It is actually a much easier read than the one I posted a link for, as it not only has all of the text that my link contained, but is more logically laid out with all those graphics seen on the pages with the discussions.  As long as it was, mine was sort of a condensed version (lacking most of the graphics).

Also thank you for the link to those Pan Am Memos, it had been a long time since I had read those.

It would probably be best for a reader to look at the Pan Am Memos first, (your link) and then go to Bob Brandenburg's exhaustive analysis of RDF bearings (the one from GL's link).

I certainly agree with you that in order to form an opinion on RADIO DIRECTION FINDER BEARINGS (your link to the Large version) that they should be approached within the context of the above 'Memos' and 'Analysis'.

I do think that the above information adds greatly to the TIGHAR hypothesis and should not be rejected outright for the reasons Gary LaPook mentioned.

The poor signal qualities at those Pan Am HF/DF stations should certainly be expected under the circumstances. 

I agree that if they had just added some 'dots' to go along with the 'dashes' that were heard as Gary pointed out would have been so simple to do, we probably would not have this marvelous mystery at all.  Since they evidently were hearing those Honolulu Radio Station KGMB broadcasts requesting the plane to transmit four long dashes on 3105 KC, perhaps KGMB could have requested some 'short dashes' in a Morse Code format along with those long dashes that were being copied.  If they were able to transmit a 'carrier' for two hours, as Gary mentioned they could have included a lot of 'code' in that time.

It seems that the small amount of "poor" code that was copied, (by other than the Pan Am Stations) was mostly just gibberish and the only 'voice' that was copied did not reveal much about location either.  There were anecdotal stories of receiving position information that was recorded and then lost long ago.  No one knows what their mental (or physical) condition was at that time.

The only hope I see to completely resolve this portion of the mystery would be to find a miraculously preserved copy of a detailed log or diary or something somewhere....

As Malcom indicated 'few of us believe in miracles' :o but that just might be possible.
Art Johnson
 
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Malcolm McKay

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #6 on: September 02, 2012, 08:21:48 PM »


We do know that the Electra Must have been on dry land, so that still limits your search to just a few islands.  The Navy initially encompassed all of the Phoenix Islands and that would have been their 'safe' estimate of the Bearing's accuracy.


And that is the problem isn't it. Yes if the post loss radio messages are to be believed but which bit of dry land. 23 years of searching Nikumaroro have failed to turn up anything that is unequivocally linked to Earhart, Noonan or the Electra. It doesn't matter that as Ric claims in another thread that people believe and continue to donate money (people contribute money to find Noah's Ark so the simple ability to part with one's money is no firm indicator of sense) - what matters is when the informed world of aviation history specialists rules a line under the hypothesis and says "yes - TIGHAR have shown that Earhart and Noonan landed on Nikumaroro".

I think that shown the latest problem discussed above regarding the post loss messages that they may be a red herring. Also the margins for error which you mention are such that accurate pin pointing of the source location or even the source itself is not that certain. As for Betty's Notebook, when TIGHAR wrote it into their hypothesis is not the issue regarding believability, the issue is its internal inconsistencies and the fact that it had been floating around for a while (offered to Goerner who advanced the Saipan theory to support him) so it is a one size fits all object.

The radio messages are just one of the reasons why I maintain that the hypothesis is a very shaky affair which relies on a whole sub set of hypotheses, each with their own uncertainties. Gary LaPook is quite sceptical and I don't think any of his objections have been answered properly. There is literally nothing in the whole evidence basket be it material, radio or whatever that can be used with 100% confidence. As someone who is used to the vagueries of data reliability that is what concerns me.

It seems to me each person who wants to believe in the hypothesis picks one sub set of data that they have a some familiarity with and uses that to claim the whole is proven - I prefer to look at the broader picture because I know that if one key plank is uncertain then the whole is uncertain.     
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Alan Harris

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #7 on: September 02, 2012, 09:24:20 PM »

The bearing that is actually not plotted, bearing 8, may provide an indication of how good some of the others were. This bearing was taken by Mokapu on 6 July at approximately 0947Z. It resulted from a scheduled attempt to take a bearing on Itasca, a target at a knowable location on a known frequency, 3105 kHz. The bearing obtained (197°) was 35° from Itasca’s true bearing (232°) at the time.

Although the quote is from Chuck Varney, I have to thank Art for bringing it here.  I knew I had read something like this recently, wasn't sure where.  Anyway, this is the sort of thing I was referring to in point (3) of my initial post introducing this topic.  Obviously, at least on its face and without backstory, it raises serious question about the potential error in RDF bearings at that period in history at that general geographical location.  I don't think anyone has really responded to what Chuck said there.  It is frustrating for an "RF lay person" like myself to see such dramatic statements thrown out and not have the background to evaluate them.  (I suppose that is kind of a naive statement, and is true for a great many people here regarding a variety of technical topics, e.g. celestial navigation to name just one other.)  What can I say, except maybe "the more discussion the better"? 
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pilotart

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #8 on: September 03, 2012, 12:40:47 AM »

Alan,

My professional field, as far as radio is concerned was as a pilot rather than a Ground Station DF Specialist, my actual experience on that end was limited to observing experts operate and explain their equipment.  This equipment looked very old then and I would guess that it was mid'50s or older.

The pilot's end of DF was limited to requesting and receiving Bearing information from the Ground Stations and using them as an aid to navigation.  40 to 50 years ago, this method was already being widely superseded by more modern methods, although there were areas where this was still the only method.  You may have read the post I made to Gary about the expected closure of the last DF Stations.

In those days, Caribbean Island Navigation was mostly done with Low Frequency "Non Directional Beacons" or Medium Frequency Standard Broadcast Stations that the Pilot would tune in and use for navigation without any input from ground stations, this is exactly what Amelia was expected to use to locate the Itasca.

Bearing 8 had not caught my attention initially because it was not a reception from the Electra.

You will notice that in my second response to Chuck I provided several links for a forum member to follow and gain knowledge on those Pan Am Bearings.

Bearing 8 is 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.

Although it is not dated (that I could see), I caught a dialogue between Ric and Gary that mentioned that the overall report on Radio Messages (the RDF signals are included within it) was just completed less than a year ago.

I had not included this report in my links provided for RDF research, but since it has the latest information, it would provide an excellent supplement to the RDF Analysis Report.

Here is page one of five long pages and you can find any individual message by date and time.

There is no doubt that DF Bearings were not always reliable as could be best illustrated by the Landing on a Reef story which seemed to result from following a series of very faulty DF Steers to a Reef a whole lot less friendly than Niku's.  Lucky they could bum a ride from those fishermen.

In addition to the Reports discussed in this thread, one of the most convincing reports for me is the comparison of Post Loss Radio reports and Tide State at Niku that synchronizes those Radio Messages with the low tides at the Norwich City Reef.  It is way beyond coincidence  to have all the Credible Post Loss Radio receptions coincide with the low tides that we know would have been necessary for radio transmissions.
Art Johnson
 
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Gary LaPook

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #9 on: September 03, 2012, 05:06:40 AM »

Regarding the Howland bearing.

It is plotted as running SSE which is equal to 157.5° (and NNW,337.5°) and was measured with a hand held magnetic compass.  This is mis-plotted because  Brandenberg did not correct for the magnetic variation that existed at Howland which causes the compass to read 9.5 degrees less than the true directions. The line should have been plotted on 167° and pass further west of Gardner. Brandenberg mentioned that magnetic variation was an issue but then didn't make the correction for it. On Howland island a compass needle points to the magnetic north pole which, from Howland, is 9.5 degrees east of true north. Since you measure clockwise from the compass needle you end up measuring a bearing that is 9.5° too small so you must add the 9.5° to correct the measured magnetic bearing of 157.5° to find the true bearing of 167° (and 347°) which is what must be plotted. It is surprising that Brandenberg didn't make this correction because Captain Dowell, commanding the Lexington group, did and put the Howland island bearing in his report as 347° true which is the correct bearing to be plotted. I have attached a pdf file consisting of a number of charts showing this. The first chart shows the bearing as plotted by Brandenberg running 157.5° true. Chart two shows the incorrect bearing and the correct, 167° true bearing and the third chart shows only the correct bearing.

The next issue is the precision of the compass reading which was measured as south-southeast, SSE, which is exactly 157.5° but don't be taken in by the seemingly half-degree precision of this marking. I have attached two diagrams of a compass card, the first one showing the compass needle lined up with the marking, SSE. The second diagram shows the compass needle pointing somewhere between SSE and SE, how would you read this? Well, if it is closer to the SE you would call it southeast but if just slightly closer to the SSE mark you will call it south-southeast. So it turns out that there is an arc 22.5° wide, 11.25° each side of SSE, that would be read out simply as south-southeast since there is no way to read it more precisely. This then adds 11.25° error bands to the Howland bearing and I have shown correct bearing plus the error bands in the fourth chart and the fifth charts just shows the 22.5° uncertainty arc. (And yes, I know a compass needle doesn't look like this, I made this diagram to illustrate the point. I have used every kind of hand compass from a Boy Scout hand compass, army lensatic compasses, to a Brunton pocket transit; marine compasses, aircraft compasses, and one of my jobs in the field artillery was using an M2 aiming circle to point the guns in the direction of fire, the M2 incorporates a compass that is accurate to a twentieth of a degree. (The photo shows a soldier using the internal compass, you look horizontally through a magnifying lens at the end of the needle inside the M2. It is because of the extreme accuracy of this compass that we could hit our targets 22,600 meters away, about 14 miles!) I also made money adjusting (determining deviation and placing small magnets to eliminate or minimize the deviation) marine compasses on sailboats.)

The next factor that needs to be considered is the additional uncertainty due to long range radio propagation. Art guessed that the accuracy should be one degree, he was overly optimistic. I have attached an excerpt from Publication 117, the official government manual on radio bearings. It states normal accuracy is two degrees for stations up to 150 NM away but that is based on best case factors. When working with a weak signal the uncertainty climbs to 10 degrees for a transmitter at only 150 NM and is greater at longer distances. Charts 6 and 7 show this additional 10 degrees of possible bearing error added to the 22.5 degree band. Also read the cautions about calibration and reciprocals, were the Pan Am direction finders calibrated in the direction of Gardner since that was not on the Pan Am flight route? The reciprocals might have different calibration correction factors so might not be exactly 180 degrees apart and this also adds to the total uncertainty bands.

Chart 8 shows the area where any station received from the south of Howland could have the bearing reported as SSE and chart 9 shows the same to the north. There are many islands in the southern area including Samoa and New Zealand. To the north, stations in Japan, China, Russia and Alaska could also have been reported as bearing SSE.

Brandenberg's report considers the possibility that the Howland bearing could have been on the same signal as the Midway bearing. In addition, his report provides another reason to doubt that the Howland bearing came from Gardner. He calculated that the signal, if it came from Gardner, should have been a strong signal as received at Howland yet the signal was reported as weak. He proposes a very weak explanation for this contradiction by saying if the antenna wires had been twisted and broken in the Howland direction finder radio that it could have made the signal weak. I think we all know that if you break the wires to the antenna in a radio then you get no reception, not just weaker reception. At least that is my experience with my ham radio antennas, lead in wire from the antenna broken, no radio signals received. Aircraft antenna disconnected, no reception.

Chart 10 also shows the similar arc of plus and minus ten degree reception uncertainty band around the rejected Midway bearing, (no additional 22.5° since the Midway RDF did read out in degrees.) You can see that these two reception areas overlap so any signal transmitted in the overlapping areas could have been reported as 175° at Midway while at the same time the reception of the same signal at Howland could have been reported as SSE and there is no way to show that this was not the case as Brandenberg's report notes.

Based on all this I believe that the Howland bearing should also be removed.

gl
« Last Edit: September 04, 2012, 04:08:28 PM by Gary LaPook »
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Alan Harris

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #10 on: September 03, 2012, 03:21:57 PM »

I have attached a pdf file consisting of a number of charts showing this.

Thank you, Gary.  As usual, your explanatory diagrams are very helpful and are "idiot-proof", even if nothing else in this detective story is.
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C.W. Herndon

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #11 on: September 03, 2012, 07:02:11 PM »

I have attached a pdf file consisting of a number of charts showing this.

Thank you, Gary. As usual, your explanatory diagrams are very helpful and are "idiot-proof", even if nothing else in this detective story is.

Not all of us would 100% agree with the part of your quote that I have highlighted thank you. ;)
Woody (former 3316R)
"the watcher"
 
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Gary LaPook

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #12 on: September 03, 2012, 11:05:17 PM »

I have attached a pdf file consisting of a number of charts showing this.

Thank you, Gary. As usual, your explanatory diagrams are very helpful and are "idiot-proof", even if nothing else in this detective story is.

Not all of us would 100% agree with the part of your quote that I have highlighted thank you. ;)

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
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Alan Harris

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #13 on: September 04, 2012, 02:10:28 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.

In my case, on first look I mistook that first line in the attachments as being just the caption for the jpeg below, and thought by clicking the jpeg I was getting all I needed.  It was only after I got through the whole sequence and still hadn't seen the promised diagrams that I looked more carefully and realized my stupid mistake.  That's my story, can't speak for others.  Missing them would be a shame, especially Charts 9 and 10 which are the heavyweights.
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C.W. Herndon

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Re: Discussions Re Radio Bearings, Fall 2012
« Reply #14 on: September 04, 2012, 04:05:02 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? ???
Woody (former 3316R)
"the watcher"
 
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