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Author Topic: Probabilities of post-loss radio signals  (Read 9875 times)

Scott C. Mitchell

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Probabilities of post-loss radio signals
« on: May 14, 2013, 10:12:53 PM »

In determining probabilities of post-loss radio signal reception, it seems to me the odds might be greater than often pronounced.  If taking into account all of the variables, let's say that the chances of a signal being received are one-in-a-thousand.  But looking at those large swathes of good transmission time, as so ably graphed out in Bob Brandenburg's article the latest TIGHAR Tracks, AE and FN may have transmitted a hundred signals for every one that was actually received.  So the odds of a few signals getting through from the full collective of signals over an extended duration, through variable conditions, should be greater than than the theoretical odds of any one particular signal.

Scott
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Matt Revington

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Re: Probabilities of post-loss radio signals
« Reply #1 on: May 15, 2013, 06:45:48 AM »

There is another way to look at the probabilities too.  If you take lottery tickets as an example, the odds of the single ticket I buy being the winning ticket might be say 50 million to one  almost vanishingly small, however when 50 million tickets with random number are sold across the country the odds of one them being a winner is pretty good.  Similarly if Betty turned on her radio with the hope of being able to hear AE then it was pretty much a fools mission however the odds of one of the thousands ( or ten of thousands) of shortwave capable radios scattered somewhat randomly around North America being in a position where a propagation path would not be too bad.  Has anyone calculated the propagation probabilities from that point of view, what would be the probability of there being point located anywhere in north america receiving a transmission.

Also I think I saw this point on another thread and I don't recall seeing an answer, were there any credible post-loss transmissions reported from Australia and if not  is there something in the propagation model that would account for this?
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Ric Gillespie

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Re: Probabilities of post-loss radio signals
« Reply #2 on: May 15, 2013, 07:51:01 AM »

Has anyone calculated the propagation probabilities from that point of view, what would be the probability of there being point located anywhere in north america receiving a transmission.

I don't know how you'd calculate that. It's not only an issue of propagation but also what kind of radio and antenna were being used.  Both Betty and Dana Randolph were using unusually sensitive antennas.

Also I think I saw this point on another thread and I don't recall seeing an answer, were there any credible post-loss transmissions reported from Australia and if not  is there something in the propagation model that would account for this?

We have one credible report from Australia (#126), a ham in Melbourne who heard a signal at the same time Navy Radio Wailupe was hearing the 281 message.
The dearth of reports from Australia probably has more to do with demographics than propagation.  For us to be aware of an alleged reception, the person hearing the transmission must have:
• owned a radio capable of receiving signals on harmonics of AE's primary frequencies
• understood the possible significance of what they were hearing
• contacted either the authorities and/or the media at the time or contacted TIGHAR later.

Those conditions were probably more commonly met in the U.S. than in Australia.
 
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Al Leonard

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Re: Probabilities of post-loss radio signals
« Reply #3 on: May 15, 2013, 11:29:49 AM »

There is another way to look at the probabilities too.  If you take lottery tickets as an example, the odds of the single ticket I buy being the winning ticket might be say 50 million to one  almost vanishingly small, however when 50 million tickets with random number are sold across the country the odds of one them being a winner is pretty good.  Similarly if Betty turned on her radio with the hope of being able to hear AE then it was pretty much a fools mission however the odds of one of the thousands ( or ten of thousands) of shortwave capable radios scattered somewhat randomly around North America being in a position where a propagation path would not be too bad.  Has anyone calculated the propagation probabilities from that point of view, what would be the probability of there being point located anywhere in north america receiving a transmission.

Also I think I saw this point on another thread and I don't recall seeing an answer, were there any credible post-loss transmissions reported from Australia and if not  is there something in the propagation model that would account for this?

Matt,

You might want to learn about the concept of provisional probability (try Wikipedia). To do what you suggest you would also need to come up with an objective determination of the false positive rate (probability that people claim to hear something they didn't) and have a plausible estimate of the population subject to false positives.

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Randy Conrad

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Re: Probabilities of post-loss radio signals
« Reply #4 on: May 15, 2013, 05:19:57 PM »

Ric...I was sitting outside the other night at home and was envisioning why Amelia and Fred were sending signals in the late hours of the night and the wee hours of the morning Pacific (Gardner) time. I don't know the exact percentage. But from most of the signals that I saw in the catalog between July 2-7...these signals were sent between 10:00PM and 5:00AM Pacific (Gardner) time. Why did she do that?

1. If you think about it...How many people are up  that late at night and early in the morning to listen to anyone sending shortwave radio messages or signals? Why not send radio transmissions during the day when someone could do a fly over and see you? Were the radio transmissions sent late at night because of desperation?

I guess why I ask these questions is because I'm not really sure Amelia or Fred were in really good shape at the time of the possible landing to making any rational decision making.

Did Amelia and Fred sleep during the day, during those 5 days of radio transmissions? Did the Electra inside temperature seem to soar as the day went along, and what was the inside temperature like? Was it bearable to sleep in those conditions, regarding someone who got hurt badly or did they seek shelter on the confines of the island?


2. Were the signals sent late at night and early hours not so much because of high/low tide, or was it because of the intense heat on the island during that time of the year?

Anyway, these are questions I have in regards to the post-loss signals. It's not that I don't believe in them....because I do. But, rather taken aside as to why these two famous people would act in that way. Like...I'm gonna go lay down now...but its 104 degrees under the tire of the Electra, but if the rescue plane flys over wake me up Fred? Now you have to remember its in the middle of the day. Or let's try again with the radio....Fred wake up...your dosing off...how are we supposed to send out anything if you keep dozin off. Now you also gotta remember its roughly between 2-5 in the morning. Most people are still asleep or are they? Anyway, these are questions I believe need to be asked, because it tells a timeline of events!!! Anyway, cmon ya all...help me out on this one!!! Thanks!!!!
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Ric Gillespie

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Re: Probabilities of post-loss radio signals
« Reply #5 on: May 15, 2013, 05:52:41 PM »

Ric...I was sitting outside the other night at home and was envisioning why Amelia and Fred were sending signals in the late hours of the night and the wee hours of the morning Pacific (Gardner) time. I don't know the exact percentage. But from most of the signals that I saw in the catalog between July 2-7...these signals were sent between 10:00PM and 5:00AM Pacific (Gardner) time. Why did she do that?

Two reasons:
•Radio propagation is best at night. 
• I have sat in an Electra cockpit in Florida on an 85° day in the shade and it was like an oven.   I can't imagine what it would be like on the reef at Niku where the temperature is similar if not higher and there is no shade.   The tropical sun on bare aluminum is something to behold.  I was on the B-17 known as "Swamp Ghost" in a swamp in New Guinea in 1986.  By 10 o'clock in the morning you couldn't touch the airplane without burning your hand.
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Laura Gridley

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Re: Probabilities of post-loss radio signals
« Reply #6 on: May 16, 2013, 02:24:53 AM »

Regarding the question about signals heard in Australia and Ric's answer--out of curiosity I looked up the population in Australia in 1937--appears it was a bit less than 7 million.  Just for comparison, US population in 1937 was around 129 million.  The lack of lack of signal reports from there being possibly due to demographics does seem logical.  (My boyfriend is from small town in southwestern australia-few hours south of Perth--and even 10 years ago it seemed quite isolated.)
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