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Points: 17493 		Direct Link To This Post Posted: April 24 2013 at 12:31
I dispute your calculations.
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Padraic View Drop Down
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 12:24
Originally posted by The Doctor The Doctor wrote:

 LOL to the power of the WTF

That's an accurate description of a lot of posts on this forum.  Wink
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Points: 37575 		Direct Link To This Post Posted: April 24 2013 at 12:23
^^ see that, the silly bugger's completely lost without his sonic screwdriver. Wink

Edited by Dean - April 24 2013 at 12:24
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 12:23
Originally posted by Dean Dean wrote:

Originally posted by Padraic Padraic wrote:

Originally posted by Dean Dean wrote:

Originally posted by Padraic Padraic wrote:

OK, so thermal noise at 300 K is -204 dBW/Hz.  I'll give you 1 kHz of bandwidth for transmission, so that gives us -174 dBW noise floor.  So you have an SNR of 40 dB, a pretty whopping signal.
Well, no - the SNR is zero - I suspect we're now at cross-purposes.

You lost me there.  -136 dBW - (-174 dBW) = 38 dB
The purpose of the exercises was to calculate the minimum transmitter power needed to achieve an SNR of zero at the receiver (with respect to the CMBR+Thermal Noise+switching and other spurious noises+Quasars and other assorted celestial noise sources) - if the back-calculation failed to do that then the transmitter output would be 38dB too big.

That's all I was getting at.  I don't think we have any more quibbles.  Smile
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Points: 8543 		Direct Link To This Post Posted: April 24 2013 at 12:22
The SNR of the DWF less the function of the square-root of the PDQ plus the LOL to the power of the WTF must be less than -.37856352746352947563554756221 of AAAGGGGHHHHH!
I can understand your anger at me, but what did the horse I rode in on ever do to you?
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Points: 37575 		Direct Link To This Post Posted: April 24 2013 at 12:19
Originally posted by Padraic Padraic wrote:

Originally posted by Dean Dean wrote:

Originally posted by Padraic Padraic wrote:

OK, so thermal noise at 300 K is -204 dBW/Hz.  I'll give you 1 kHz of bandwidth for transmission, so that gives us -174 dBW noise floor.  So you have an SNR of 40 dB, a pretty whopping signal.
Well, no - the SNR is zero - I suspect we're now at cross-purposes.

You lost me there.  -136 dBW - (-174 dBW) = 38 dB
The purpose of the exercises was to calculate the minimum transmitter power needed to achieve an SNR of zero at the receiver (with respect to the CMBR+Thermal Noise+switching and other spurious noises+Quasars and other assorted celestial noise sources) - if the back-calculation failed to do that then the transmitter output would be 38dB too big.
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 11:31
Originally posted by Dean Dean wrote:

Originally posted by Padraic Padraic wrote:

OK, so thermal noise at 300 K is -204 dBW/Hz.  I'll give you 1 kHz of bandwidth for transmission, so that gives us -174 dBW noise floor.  So you have an SNR of 40 dB, a pretty whopping signal.
Well, no - the SNR is zero - I suspect we're now at cross-purposes.

You lost me there.  -136 dBW - (-174 dBW) = 38 dB
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Points: 14693 		Direct Link To This Post Posted: April 24 2013 at 11:27
Which is as good a time as any for a break & a word from our sponsors



...and we're back

Edited by Jim Garten - April 24 2013 at 11:28

Jon Lord 1941 - 2012
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Points: 37575 		Direct Link To This Post Posted: April 24 2013 at 11:16
Originally posted by Padraic Padraic wrote:

OK, so thermal noise at 300 K is -204 dBW/Hz.  I'll give you 1 kHz of bandwidth for transmission, so that gives us -174 dBW noise floor.  So you have an SNR of 40 dB, a pretty whopping signal.
Well, no - the SNR is zero - I suspect we're now at cross-purposes.
Originally posted by Padraic Padraic wrote:

I'm not saying you don't need a shedload of power - you most obviously do, we're probably quibbling over a few orders of magnitude of power levels that exceed that what the entire planet consumes.
Aye, and consumption levels are several magnitudes higher than what leaks out into space.
Originally posted by Padraic Padraic wrote:

Bottom line is we agree on the broader point that thanks to all this geekery I've now forgotten.
Aye.
 
Originally posted by Dean Dean wrote:

Please explain how our presence on this planet would be easily detectable - please feel free to be as technical as you like, it's been 30 years since I studied telecommunications at University but I'm sure it will all come back to me.
... apparently not as quickly as I would have hoped. LOL
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 10:49
OK, so thermal noise at 300 K is -204 dBW/Hz.  I'll give you 1 kHz of bandwidth for transmission, so that gives us -174 dBW noise floor.  So you have an SNR of 40 dB, a pretty whopping signal.

I'm not saying you don't need a shedload of power - you most obviously do, we're probably quibbling over a few orders of magnitude of power levels that exceed that what the entire planet consumes.

Bottom line is we agree on the broader point that thanks to all this geekery I've now forgotten.
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Points: 37575 		Direct Link To This Post Posted: April 24 2013 at 10:39
Originally posted by Padraic Padraic wrote:

Here, try plugging some numbers into this and see if your zettawatt number makes sense.
 
 
Okay did that - arrived at -136dBW, which equates to 21.7fW
 
That would look like snow on my old Sony TV
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 10:11
Here, try plugging some numbers into this and see if your zettawatt number makes sense.
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 10:09
10*log10(40e-15 * 3e8) + 30
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Points: 37575 		Direct Link To This Post Posted: April 24 2013 at 10:07
Originally posted by Padraic Padraic wrote:


Units are indeed correct, but the magnitude implies that if I have a 1 m2 antenna I would be receiving a power of -19.2 dBm from the CMBR, which can't be true.
 
Originally posted by Padraic Padraic wrote:

That number seems high. Please show your work. Wink
 
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 10:01
VOGON CAPTAIN:
There's no point in acting all surprised about it. All the planning charts and demolition orders have been on display at your local planning department in Alpha Centauri for fifty of your Earth years so you've had plenty of time to lodge any formal complaints and its far too late to start making a fuss about it now. 

MANKIND:
[Louder yells of protest] 

VOGON CAPTAIN:
What do you mean you've never been to Alpha Centauri? Oh for heaven sake mankind it's only four light years away you know! I'm sorry but if you can't be bothered to take an interest in local affairs that's your own regard. Energise the demolition beams! God I don't know…apathetic bloody planet, I've no sympathy at all… 

Tongue
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Points: 8543 		Direct Link To This Post Posted: April 24 2013 at 09:56
^LOL I should've known.  -19.2 dBm. CMBR.  Pah! It doesn't even sound like real stuff, now that my morning fog is starting to lift finally.
I can understand your anger at me, but what did the horse I rode in on ever do to you?
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Points: 14693 		Direct Link To This Post Posted: April 24 2013 at 09:49
Don't worry about it Chester

Quote I have a 1 m2 antenna I would be receiving a power of -19.2 dBm from the CMBR


They're just putting together random collections of numbers & letters now.

Personally I thought it was self evident that a +/- ratio of Pi to the power of x/y (where y is a constant N factor, of course) would result if an amplitude gain sufficient to reach Proxima Centuri.

See?

Jon Lord 1941 - 2012
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Points: 8543 		Direct Link To This Post Posted: April 24 2013 at 09:38
My brain just melted. 
I can understand your anger at me, but what did the horse I rode in on ever do to you?
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Points: 31169 		Direct Link To This Post Posted: April 24 2013 at 09:36
Originally posted by Dean Dean wrote:

Originally posted by Padraic Padraic wrote:

Sorry.  Normally this is the sort of thing Dean and I could work out at the pub, but there's a big pesky ocean in the way.
To the inevitable dismay of our respective partners and anyone else drinking with us, this would be true.
 
We'd propbably work out how long the journey would take at Warp 8 and when Voyager 1 will get there for good measure.
 
Anyway, just done a quick dimensional analysis check on the formula I used and the value I calculated has units of J/s, which is power. Can't see an error in the magnitudes of the numbers either so I'm sticking to 240 zettawatts, a high-gain antenna would reduce that to 2.4etawatts if the power didn't vapourise it at switch-on.

Units are indeed correct, but the magnitude implies that if I have a 1 m2 antenna I would be receiving a power of -19.2 dBm from the CMBR, which can't be true.
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Points: 8543 		Direct Link To This Post Posted: April 24 2013 at 07:55
Originally posted by Jim Garten Jim Garten wrote:

Git!

[edit]

Anyway - even at 07:32, I'd (probably) worked out which way was up & was then working on the multitasking conundrum that is first coffee & cigarette of the day!

That's as far as I get of a morning.



This + I'm still trying to convince myself that it wouldn't just be better for all concerned if I called it a day and went back to bed. 
I can understand your anger at me, but what did the horse I rode in on ever do to you?
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