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Author Topic: Post-Loss Radio Signals  (Read 82944 times)

Gary LaPook

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Re: Post-Loss Radio Signals
« Reply #45 on: October 25, 2011, 01:02:47 PM »

Maybe this view is better - 1936 map notes mention that this map shows:

Time zone boundaries and clocks showing the time when it is midnight at Greenwich


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You have to look at the clock images at the bottom of the map to see the time for that particular time zone. The clock images you noticed are the exceptions to the standard time kept only on the land located next to those clock faces.

gl
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Gary LaPook

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Re: Post-Loss Radio Signals
« Reply #46 on: October 25, 2011, 01:05:59 PM »

I don't know what your source is for Earhart setting her cockpit clock to local time at the departure airport, but I do know that she told Itasca to use GCT for radio schedules during the Lae/Howland flight (an instruction that Itasca ignored).  How AE and FN calculated local time on Gardner, if they bothered, is both unknowable and irrelevant.  We included the best available calculation of local time on Gardner in the 1937 context primarily to provide a sense of the time of day for the reader.  If Amelia and Fred thought it was 10 P.M. when we say it was 9 P.M. it has no bearing on the credibility of a radio signal heard at that time as long as the Zulu (Greenwich) time is correct.

BTW, we use Zulu as local time for signals heard by Pan Am stations at Mokapu, Midway, and Wake because Pan American, alone among all the stations involved, kept their radio schedules in Greenwich time.  They were way ahead of the game.
---------------------------------

That's easy, Earhart's notes on the flight from Natal to Dakar.

gl
« Last Edit: July 21, 2012, 10:57:17 AM by J. Nevill »
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Sheila Shigley

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Re: Post-Loss Radio Signals
« Reply #47 on: October 25, 2011, 02:13:36 PM »

But the radio log kept by the radio operators actually ashore on Howland used Z.D. +10:30 not + 11:30.

Sorry. I misspoke.  We use +11:30 for Itasca.  We use +10:30 for Howland for the reason you cite.

And this is Z.D., meaning Itasca +11:30 = Zulu, and Howland +10:30 = Zulu, correct?

Itasca was 11:30 behind Zulu; Howland was 10:30 behind Zulu

Done the other way, this would be Itasca -11.5 and Howland -10.5 (Itasca local = Zulu -11.5; Howland local = Zulu -10.5)

Whew.
« Last Edit: October 25, 2011, 02:17:43 PM by Sheila Shigley »
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Sheila Shigley

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Re: Post-Loss Radio Signals
« Reply #48 on: October 25, 2011, 02:23:45 PM »

Non-Z.D. method (caculate local from Zulu) (What's correct term for this - offset?)

Itasca local:  Zulu -11.5
Gardner local:  Zulu -11
Howland local:  Zulu -10.5

Z.D. method (calculate Zulu from local)

Itasca:  Z.D. +11.5
Gardner:  Z.D. +11
Howland: Z.D. +10.5

 
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Gary LaPook

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Re: Post-Loss Radio Signals
« Reply #49 on: October 25, 2011, 02:33:28 PM »

Non-Z.D. method (caculate local from Zulu) (What's correct term for this - offset?)

Itasca local:  Zulu -11.5
Gardner local:  Zulu -11
Howland local:  Zulu -10.5

Z.D. method (calculate Zulu from local)

Itasca:  Z.D. +11.5
Gardner:  Z.D. +11
Howland: Z.D. +10.5
--------------------------

For Gardner you state Ric's usage correctly. For the common usage however, not Ric's, it would be Zulu  -12. If you don't believe me, just go to the bottom of the 1936 National Geographic Map that you posted, directly down from Gardner, where you will find a clock face displaying "12:00 NOON." The white vertical lines are the boundaries between the time zones. (Note that is is 12:00 NOON on both sides of the 180th meridian but the dates are different.)

gl

gl
« Last Edit: October 25, 2011, 02:44:51 PM by Gary LaPook »
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Gary LaPook

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Re: Post-Loss Radio Signals
« Reply #50 on: October 25, 2011, 02:52:43 PM »

That's fine but you stated your purpose was to let the reader know what the castaways would observe on Gardner, not what the sailors on ships operating in the vicinity would observe.

That's not what I said.  I said, "We included the best available calculation of local time on Gardner in the 1937 context primarily to provide a sense of the time of day for the reader."  By "sense of time of day" I mean early morning, late morning, afternoon, evening, late at night, etc.  That's hard to get from Zulu time.

Either you should not call it "Gardner time" or you  should include a warning:

"WARNING, WHAT WE HAVE LISTED AS 'GARDNER TIME' IS ACTUALLY NOT WHAT WOULD HAVE BEEN OBSERVED ON GARDNER. IT IS ACTUALLY THE TIME OBSERVED ON NAVY SHIPS PARTICIPATING IN THE SEARCH AND IS ACTUALLY AN HOUR FAST ON WHAT WOULD HAVE BEEN OBSERVED BY EARHART AND NOONAN"

We don't know, and don't have any way of knowing, what local time Earhart and Noonan "observed" on Gardner - nor does it matter.  To include the statement you suggest would be to assert that we know something we can not possibly know. In historical writing "would have" is a guess masquerading as fact.  We have had this discussion before.  If you ever catch me pulling a "would have" jump all over me.  It's one of the most dangerous mistakes an investigator can make.
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Since I was talking about natural phenomena on which there can be no disagreement, such as the earth rotating on its axis, the sun rising in the east, etc. you are right, Ric, I should not have used the conditional tense with the formulation, "WOULD HAVE BEEN" but should have used simply "WAS." Here is the corrected warning for your index:

"WARNING, WHAT WE HAVE LISTED AS 'GARDNER TIME' IS ACTUALLY NOT WHAT WAS OBSERVED ON GARDNER. IT IS ACTUALLY THE TIME OBSERVED ON NAVY SHIPS PARTICIPATING IN THE SEARCH AND IS ACTUALLY AN HOUR FAST ON WHAT WAS OBSERVED BY EARHART AND NOONAN"

gl
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Don Dollinger

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Re: Post-Loss Radio Signals
« Reply #51 on: October 25, 2011, 03:40:36 PM »

Gary,

Don't know if I should poke my nose in here BUT...

Quote
For Gardner you have Ric's usage correct. For the common usage, not Ric's, it would be Zulu  -12.

Quote
You keep citing regulations and I'll keep citing reality.  The ships' logs consistently used half hour time zones when they were underway, far from land or other ships.

I have fallen into this same trap and can tell you from experience that what the regulation states and what is actually done can and does differ.  Some people don't know what the regulation states, some don't care what the regulation states, and some know what the regulation states but also knows what works and that is what they use. That is the "reality" Ric speaks of.

LTM,

Don

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Gary LaPook

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Re: Post-Loss Radio Signals
« Reply #52 on: October 25, 2011, 03:48:04 PM »

Gary,

Don't know if I should poke my nose in here BUT...

Quote
For Gardner you have Ric's usage correct. For the common usage, not Ric's, it would be Zulu  -12.

Quote
You keep citing regulations and I'll keep citing reality.  The ships' logs consistently used half hour time zones when they were underway, far from land or other ships.

I have fallen into this same trap and can tell you from experience that what the regulation states and what is actually done can and does differ.  Some people don't know what the regulation states, some don't care what the regulation states, and some know what the regulation states but also knows what works and that is what they use. That is the "reality" Ric speaks of.

LTM,

Don
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But the issue of what "time" to associate with Gardner has nothing to do with whether the ships were following regulation and it appears that they were following the exception contained in the regulation for operational convenience, which I agree is the correct thing for those ships to do. But for people reading the listing and wanting to know what time was observed on Gardner, basically what time the sun rose and set, the time of noon and of the tides, using those ships' time does not accurately depict what people on Gardner in July 1937 observed.

gl
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Gary LaPook

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Re: Post-Loss Radio Signals
« Reply #53 on: October 25, 2011, 05:16:11 PM »

And in 1937, Howland and Gardner were still in different time zones, correct?

According to Gary, Howland and Gardner were officially both in the 12 hour time zone.  That's fine, but none of the ships used it.

Oops - I'd better qualify that - for our purposes both Howland and Gardner are -11 offset from Zulu, meaning 11 hours behind Zulu, correct?  Zulu -11 = Howland local, and Zulu -11 = Gardner local?
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I have attached table 36 from The American Practical Navigator, the standard navigational textual authority published by the the U.S. Navy Hydrographic Office as Publication Number 9 (H.O. 9). The American Practical Navigator has been accepted as the ultimate reference in the U.S. for well over a hundred years. This table shows the standard time zones and Zone Descriptions.

gl
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Gary LaPook

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Re: Post-Loss Radio Signals
« Reply #54 on: October 25, 2011, 05:35:38 PM »

Here are the entries in "Messages July 3, 1 – 47" (http://goo.gl/Pqm2x) where Gardner is listed as something other than -11:

Thanks Sheila.  We'll take a look at those and change them - or if we think they're right we'll explain why.
We want this thing to be right in every respect.
-------------------------
I don't plan to go over all the entries and I do thank you for your work on this project. But I do have a question about the third entry:

"Identifier    30200MC
Z Time/Date    0200 July 3
Local Time/Date    1800 PST July 2
Gardner Time/Date    1500 July 2
Agency/Person    Walter McMenamy, radio amateur
Location    Los Angeles "

My question is how was the Z time arrived at? Presumably you started with McMenamy's time, which was California time, and converted it to Z time. You did this by adding 8 hours to his 1800 and arrived at 2600 which is 0200 the next day, July 3rd. But this was in July and they were probably ( I am not sure of this) on daylight savings time so the correct Z.D. most likely should have been +7 making the correct Z time 0100 July 3rd and the time at Gardner (using your method) 1400 July 2nd and 1300 using the standard method.

gl
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Ric Gillespie

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Re: Post-Loss Radio Signals
« Reply #55 on: October 25, 2011, 05:36:56 PM »

...using those ships' time does not accurately depict what people on Gardner in July 1937 observed.

Pssst, Gary...there were no people living on Gardner in 1937 - except AE and FN - and it doesn't matter what local time they "observed."  It does matter what time the sun rose and set and at what time the tides went in and out, but for that we use Greenwich time.  We likewise use Greenwich when we're comparing what radio signals were heard by whom and when.  Local time on Gardner is a non-issue.  When the island was eventually settled, the people who lived there didn't observe official local time. When Paul Laxton was there in 1949 he was amazed to discover that the sun came up every day at exactly 6 A.M. until he discovered that everyone set their clocks to 6 A.M. when the sun came up.

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Ric Gillespie

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Re: Post-Loss Radio Signals
« Reply #56 on: October 25, 2011, 05:48:07 PM »

My question is how was the Z time arrived at? Presumably you started with McMenamy's time, which was California time, and converted it to Z time. You did this by adding 8 hours to his 1800 and arrived at 2600 which is 0200 the next day, July 3rd. But this was in July and they were probably ( I am not sure of this) on daylight savings time so the correct Z.D. most likely should have been +7 making the correct Z time 0100 July 3rd and the time at Gardner (using your method) 1400 July 2nd and 1300 using the standard method.

The question of whether a particular location was or was not using Daylight Savings Time in 1937 was an issue we had to address with all of the U.S. domestic reports. At that time, use of DST was spotty.  Verifying the correct conversion was a pain but we did it. That's one of many reasons it took us twelve years to compile this thing.  To say for sure what source we used to verify that L.A. was not on DST I'd have to dig back through the records.  Please feel free to check our work.
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Ric Gillespie

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Re: Post-Loss Radio Signals
« Reply #57 on: October 25, 2011, 05:53:17 PM »

I don't know what your source is for Earhart setting her cockpit clock to local time at the departure airport,
---------------------------------

That's easy, Earhart's notes on the flight from Natal to Dakar.

In her notes Earhart writes, "9:41 Natal time.  Clouds seem to be changing. (etc.)"  Is it from that that you conclude  "her practice was to leave her clock set to the time at the departure airport."?  It seems to have been her practice on the South Atlantic crossing but on that flight - and, as far as we know, on all flights except the Lae/Howland flight - she didn't expect to keep any radio schedules.  For the Lae/Howland flight she specifically said she would use Greenwich time.
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Chuck Varney

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Re: Post-Loss Radio Signals
« Reply #58 on: October 28, 2011, 07:19:07 AM »

Thank you, Ric and Bob, for organizing and analyzing the mass of post-loss signal reports, and for publishing the results of your labors.

Perhaps you can answer some questions I have relating to reception probability in the catalog.
 
1.  What transmitter powers were input to ICEPAC for operation at 3105 kHz and its harmonics?

2.  What transmitter powers were input to ICEPAC for operation at 6210 kHz and its harmonics?

3. What values of ICEPAC “signal statistics” were used to calculate the probability of 0.0013 given in message 142 (Identifier 52130KK)?  (These presumably would be the values for the input parameter, REQ. SNR, and the outputs, SNR and SNR UP.)

4. What values were used for the 0.00000067 probability, same message?

5. What SSN values were used for 3. and 4.?

Chuck
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Bob Brandenburg

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Re: Post-Loss Radio Signals
« Reply #59 on: October 28, 2011, 02:43:00 PM »

Chuck:

1. and 2. The values are in my research paper "WE-13C Transmitter Harmonic Power Output" on the TIGHAR website.

3.  REQ = 44 dB;  SNR= -3 dB, SNRUP = 20.0 dB.

4.  REQ = 44 dB;  SNR = 7 dB,  SNRUP = 9.8 dB.

5.  SSN = 91.

Bob
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