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Re: LF: MF 630m: False Decode or Real?

To: <[email protected]>
Subject: Re: LF: MF 630m: False Decode or Real?
From: "Alan Melia" <[email protected]>
Date: Thu, 21 May 2015 17:47:50 +0100
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A couple of comments on the statistics......this has little to do with the decode process itself.
The timing only goes to show that the "decoded" call sign was active at the
time NOT that he was really received, but might have been.
Graham thinks that because there were no more false decodes in the previous
24 hours this one MUST be good. Statistics dont work like that ! If it is a
million to one for a false decode you must expect at least near to a million
decodes before another false one. On the contrary 2 questionable decodes of
the same call would be extremely unlikely to be a random correlation so
would provide good evidence the call was actually received and decoded
properly. The probability of one true decode but not a second due to fading
is very (very) low but not impossible.
Next though many do not seem to appreciate it, statistics dont "prove"
anything, they provide a measure of the probability of an expected outcome.
You determine both the probability of the expected outcome and also the
probability it could be just random chance. The bigger the difference then
the more likely the expected event occured. This is what makes a second
decode so powerful.
People DO win the lottery every week! So false decodes do happen by
chance.....but the same lottery winners rarely win two weeks in succession.
Alan
G3NYK




----- Original Message ----- From: "Mike Dennison" <[email protected]>
To: <[email protected]>
Sent: Thursday, May 21, 2015 5:04 PM
Subject: Re: LF: MF 630m: False Decode or Real?


Very likely a false decode. The clue is the two question marks. In my
experience, almost every decode with question marks is false, and
there are very few cases where these particular decodes are useful. I
believe it would be helpful not to display these at all.

Having said that, the deep search facility in Opera is very useful
and has revealed some very interesting propagation information. But
only using the decodes without the question marks which, again in my
experience, are almost always genuine.

Mike, G3XDV
===========

Just popped up at my RX:

17:52    477 VK3ELV de DF1VB/3 Op8 Deep Search ?? 16348 km -37 dB in
Dortmund with 140w + Top loaded L 18m vert 80m horz

Any comments welcome

73, Jochen



--
  -= DF1VB =-
  -= KH2MM =-
Jochen Althoff
+49 171 2020206

"The wireless telegraph is not difficult to understand.
The ordinary telegraph is like a very long cat.
You pull the tail in New York, and it meows in Los Angeles.
The wireless is the same, only without the cat."
(Albert Einstein)



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