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Author | Message |
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Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Good morning again, Hopefully I'll run out of questions soon for today. ; ) Anyway, I'm trying to compose a hypothetical signal (for my writing project), and this is what I have so far. Can anyone tell me if this can be decoded? (It actually does make sense, but maybe only to me.) Don't think of the four lines as following one after the other, but as simultaneous strings of pulses or spaces. 10011000000001000011011 01000000000000100000000 00000100010010000000000 00000010000000000000000 Dave |
John Chrzastek Send message Joined: 28 May 12 Posts: 45 Credit: 29,723,112 RAC: 0 |
Did you mean this to be a very large binary number whose most significant member would be 2 raised to the 92nd power ( approx. 4.95 to the 27th power - in base 10)? |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
No, I'm not that smart. ; ) (Seriously, I'm not!) I actually re-formatted it in a way that might be easier to decipher. Think of this as being transmitted in a signal with two different polarities (I don't even know for sure if what I'm thinking is possible). Maybe it needs to be two different frequencies altogether, I'm not sure. Anyway, an X is a pulse, while a - is a null or lack of a pulse. Note there are sometimes nulls in both strings at the same time, which is a key feature. Polarity A (or Frequency A): X-X--XX-X-X---X--X-X-X----XX-XX Polarity B (or Frequency B): ---X-------XX--XX-----XXX---X-- Time progresses left to right. Basically, I'm trying to determine if my fictional signal a) makes sense, b) can be deciphered, and c) is technically feasible (re: different signals on the same frequency but at different polarities [or two different frequencies as a last resort]). Dave |
John Chrzastek Send message Joined: 28 May 12 Posts: 45 Credit: 29,723,112 RAC: 0 |
Apparently it is possible to transmit in two polarities at the same time (H & V) per http://www.patents.com/us-7245669.html. Not sure why you would want to do that but if your hypothesizing some extra-terrestrial I suppose anything is possible and maybe they've figured something out that we over-looked? |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
I was thinking pulses in one polarity would be ones, and pulses in the other polarity would be zeros. Intervals with no pulse in either polarity would act as punctuation of a sort. Basically, in my twisted logic (TM), the entire thing reads 1 2 3 1 4 9 1 8 27 - 1, 2 and 3 to the first, second and third powers. Yeah, I'm not the brightest guy. ; ) |
John Chrzastek Send message Joined: 28 May 12 Posts: 45 Credit: 29,723,112 RAC: 0 |
OK, now I understand the message you want to transmit: 1, 2, 3, 1, 4, 9, 1, 8, 27. So now I need to understand the format of each character field. How does a 1 differ from a 2 or a 3 etc. What does a space/null look like? Are you going to signal a start and stop - or just repeat the sequence for a finite length of time and then just stop? Since you seem to be headed in a binary direction ... 2 states on or off ... horizontal or vertical ... and your largest number is 27, you would need 5 binary digits 2 to the 5 = 32 so you could go as high as 32 00000=0 00001=1 00010=2 00011=3 00100=4 00101=5 00110=6 ... 01000=8, 01001=9,... 11011=27. So a 9 would look like HVHHV (or VHVVH)and a 27 would be HHVHH (or VVHVV). Implicit in this system is that the "bits" are uniform in length (time) and so are the null spaces (consisting of neither H or V). How many bit spaces do you want your nulls to take up? That's all I can think of at the moment but it seems to satisfy the requirements of your signalling system. |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
I'm not quite sure I follow (it's my shortcoming, not yours!) - let me know if I'm on the right track. 1s, 0s and nulls all have the same duration, let's just say one second. Should I make the nulls a multiple of a single duration, two seconds or more? What was a 2, with a single null separating each repetition... H--H- -V--V should now be something like... H----H- -V----V in this case with three nulls as a separator? There wouldn't be an actual start/stop signal; hopefully the double null (a null in both polarities at the same time, of whatever duration) would signal that it's time to start decoding a new binary number. Mr. Remedial Math here (me) assumes a binary wouldn't start with a zero, so that should be a sign that they're swapping the 1 and 0 values for the two different polarities. If they see a number starting with a 0, they know they've got it flip-flopped. Now, do you suggest that each binary number take up the same number of intervals? For instance: 27 = HH-HH --V-- 1 = H---- ----- I was thinking that each number would take up its native number of intervals - two intervals for a 1, five intervals for a 27 - and the dual-polarity null separators would be the same length all the time, whether one duration or a multiple of that. So maybe the old string (note a double null, simultaneously in the H and V polarities, separating binary numbers): H-H--HH-H-H---H--H-H-H----HH-HH ---V-------VV--VV-----VVV---V-- Should be something like this for better clarity, with three (or any number above one) null intervals between binary numbers: H-H----HH---H-H-----H--H---H-H------HH-HH ---V-----------VV----VV-------VVV-----V-- I hope I'm explaining, and more importantly, questioning clearly! Dave |
Julie Send message Joined: 28 Oct 09 Posts: 34053 Credit: 18,883,157 RAC: 18 |
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rob smith Send message Joined: 7 Mar 03 Posts: 22216 Credit: 416,307,556 RAC: 380 |
There are a couple of issues with your proposed encoding system, first is, polarisation can be affected very significantly of stellar distances, what started out as one polarisation can be "smudged" into another, or one can be totally "lost". When working with nulls, you need to ensure that their is adequate synchronisation, or accurate timing, and repeated nulls can all to readily be miss interpreted as loss of signal. In designing encoding techniques for long distances you have to be very careful to ensure that both ends will know what is expected to make a valid message so can perform on the fly checks. Bob Smith Member of Seti PIPPS (Pluto is a Planet Protest Society) Somewhere in the (un)known Universe? |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Hi Rob, Thanks for the suggestions! So maybe instead of polarization I should use two different frequencies? I was originally thinking about hydrogen and hydroxyl, but I thought that they're far enough apart that someone searching for a signal might not pick up on both. Or possibly hopping from a few Hz below 1420 for zeroes and a few Hz above 1420 for ones? As for the duration of each pulse or null, I was thinking somewhere around 10 seconds (obviously not exactly 10 - ET wouldn't know what a second is), with maybe a three second integration time (which seems to be somewhat common for at least some programs). By keeping the pulses and nulls relatively short, I was thinking that there would be enough time for a repeat of the signal that it would be apparent a null stretch wouldn't be signal loss. Going back to the hopping above and below 1420 - maybe a string of "zero" pulses and nulls a little below 1420, a string of "one" pulses above 1420, and a continuous beacon right at 1420. I know that power requirements make a continuous beacon problematic, but I'm hoping my ETs have found a way to get around that. ; ) Dave PS: I've been running SETI@home off and on for the last few years, and continuously now on a dedicated Linux laptop for the last few months. I'm sure I'm way down the list in work completed, but it's still fun to be involved. Total credit 507,883 Recent average credit 1,980.95 |
William Rothamel Send message Joined: 25 Oct 06 Posts: 3756 Credit: 1,999,735 RAC: 4 |
You should propose a carrier frequency at the Lyman Line of Hydrogen and perhaps π times that frequency. It will already be shifted somewhat when it reaches the recipient due to the Doppler effect. The carrier is then Modulated; you can use Amplitude Modulation or Frequency Modulation; perhaps you may just switch the carrier on and off. You might use a more sophisticated form of modulation like QAM or single sideband FM. You could use two tones for on and off separated by a pause between, say, counts. You could count out the prime numbers up to the first 50 of them followed by the first 50 digits of π. This would catch someone's attention. I would then send a pictograph and/or a video frame. This should contain information as to the location of your home planet. I would blast high power repeats of this message to promising stars in our Galaxy. A reply may not come for many decades even if it is received successfully. The receipt of such a message at these frequencies would provide incontrovertible evidence that there is intelligent life out there in the Milky Way Galaxy. |
anniet Send message Joined: 2 Feb 14 Posts: 7105 Credit: 1,577,368 RAC: 75 |
Taking a look... Me too :) very interesting... though can't contribute much... other than a lot of blinking :) |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Thanks William! I read up a bit on Lyman lines (until I got tangled in a bunch of Greek letters!), so I have a very basic understanding of them, but I don't know why such a frequency (times whatever) would be better than 1420 MHz. What would the benefits of a modulated carrier be over one that's CW? (Less stress on the transmitter?) Dave |
rob smith Send message Joined: 7 Mar 03 Posts: 22216 Credit: 416,307,556 RAC: 380 |
Dave, Well done on the crunching front. Frequency shift modulation is better over long distances as the differences will be preserved even if the timing goes to astray. Google FSK, FSC and "Frequency Shift Carrier". Bob Smith Member of Seti PIPPS (Pluto is a Planet Protest Society) Somewhere in the (un)known Universe? |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Thanks Rob! I found a decent overview of FSC at Wikipedia, "the source for all things mostly accurate." ; ) It looks like FSC might be exactly what I'm looking for. Dave |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Hi Chris, Thanks for the reply! I looked online for the book and found a copy at Amazon, but there's zero information - no author, no summary, no publisher - so I'm not absolutely sure if it's the same book, despite the title. However, Duncan Lunan has a website of his own (http://www.duncanlunan.com/), and although he doesn't sell the book there, there's some information that might be helpful (I'll still poke around online to find a copy). He also has an article published there that might be of interest, "Epsilon Bootis Revisited" (http://www.duncanlunan.com/epsilonbootis.asp). Dave |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Part two. I did a real Amazon search, rather than one through Google, and found the book, as well as a couple of others that might be good - "The Mysterious Signals From Outer Space" and "Interstellar Contact." He's quite a prolific writer, some in science fiction, but if he's taken a serious look at the subject in these other books the information could be useful. Thanks for the tip! Dave |
William Rothamel Send message Joined: 25 Oct 06 Posts: 3756 Credit: 1,999,735 RAC: 4 |
What you should do for inspiration is to read the novel and watch the movie titled "CONTACT" |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Actually, I've done both. I'm hoping to take that basic idea but make it more realistic. Overall I liked them, each in different ways, but I felt the "eccentric rich guy goes to space" was a bit too much... too Hollywood-y. ; ) There'd be no futuristic machine in mine, no attempt to travel any further than halfway around the world. As much as practical, I want to show what it would really be like. |
Dave Send message Joined: 27 May 09 Posts: 54 Credit: 1,932,495 RAC: 1 |
Hi Chris, I have a quick question for you - is there a benefit of using FSK instead of Amplitude SK for long distance transmissions? Dave |
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