gyansorova@gmail.com writes:> On Jun 19, 12:26 pm, Randy Yates <y...@ieee.org> wrote: >> gyansor...@gmail.com writes: >> > We are often told that our earliest TV and radio signals are out there >> > in space travelling at the speed of light. But doesn't the power go >> > down by the inverse square law? Also what about additive noise? Surely >> > if anybody 60 light years away was to listen they would hear only >> > noise? >> >> > W.King >> >> Hi W.King, >> >> Yes, the power goes down by the inverse square law. However, power alone >> doesn't dictate receivability. What also matters is the bandwidth and >> the noise temperature of the receiver, which can be made arbitrarily >> small. >> >> Notice also that there is no "additive noise" in space except for >> blackbody radiation, and that depends on where your receive antenna >> is looking. Otherwise the noise is set by the noise temperature of >> the receiver's front-end. >> -- >> % Randy Yates % "Bird, on the wing, >> %% Fuquay-Varina, NC % goes floating by >> %%% 919-577-9882 % but there's a teardrop in his eye..." >> %%%% <y...@ieee.org> % 'One Summer Dream', *Face The Music*, ELOhttp://home.earthlink.net/~yatescr > > > So has anybody done the Maths - say 60 light years at the power output > from a typical National Radio station of the time. Would have been AM > with a bandwidth say 5kHz.http://www.satsig.net/seticalc.htm -- % Randy Yates % "Bird, on the wing, %% Fuquay-Varina, NC % goes floating by %%% 919-577-9882 % but there's a teardrop in his eye..." %%%% <yates@ieee.org> % 'One Summer Dream', *Face The Music*, ELO http://home.earthlink.net/~yatescr
OT: TV and radio signals in Space
Started by ●June 18, 2007
Reply by ●June 18, 20072007-06-18
Reply by ●June 18, 20072007-06-18
gyansorova@gmail.com writes:> On Jun 19, 12:26 pm, Randy Yates <y...@ieee.org> wrote: >> gyansor...@gmail.com writes: >> > We are often told that our earliest TV and radio signals are out there >> > in space travelling at the speed of light. But doesn't the power go >> > down by the inverse square law? Also what about additive noise? Surely >> > if anybody 60 light years away was to listen they would hear only >> > noise? >> >> > W.King >> >> Hi W.King, >> >> Yes, the power goes down by the inverse square law. However, power alone >> doesn't dictate receivability. What also matters is the bandwidth and >> the noise temperature of the receiver, which can be made arbitrarily >> small. >> >> Notice also that there is no "additive noise" in space except for >> blackbody radiation, and that depends on where your receive antenna >> is looking. Otherwise the noise is set by the noise temperature of >> the receiver's front-end. >> -- >> % Randy Yates % "Bird, on the wing, >> %% Fuquay-Varina, NC % goes floating by >> %%% 919-577-9882 % but there's a teardrop in his eye..." >> %%%% <y...@ieee.org> % 'One Summer Dream', *Face The Music*, ELOhttp://home.earthlink.net/~yatescr > > > So has anybody done the Maths - say 60 light years at the power output > from a typical National Radio station of the time. Would have been AM > with a bandwidth say 5kHz.http://www.satsig.net/seticalc.htm -- % Randy Yates % "Bird, on the wing, %% Fuquay-Varina, NC % goes floating by %%% 919-577-9882 % but there's a teardrop in his eye..." %%%% <yates@ieee.org> % 'One Summer Dream', *Face The Music*, ELO http://home.earthlink.net/~yatescr
Reply by ●June 18, 20072007-06-18
Randy Yates <yates@ieee.org> writes:> [...] > http://www.satsig.net/seticalc.htmI didn't look too closely, so I don't know what else you'd need to do, but you could derate the transmit power (or size, or both) to simulate isotropic/non-directional radiation. -- % Randy Yates % "Though you ride on the wheels of tomorrow, %% Fuquay-Varina, NC % you still wander the fields of your %%% 919-577-9882 % sorrow." %%%% <yates@ieee.org> % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr
Reply by ●June 18, 20072007-06-18
On Jun 19, 1:57 pm, Randy Yates <y...@ieee.org> wrote:> Randy Yates <y...@ieee.org> writes: > > [...] > >http://www.satsig.net/seticalc.htm > > I didn't look too closely, so I don't know what else you'd need to do, > but you could derate the transmit power (or size, or both) to simulate > isotropic/non-directional radiation. > -- > % Randy Yates % "Though you ride on the wheels of tomorrow, > %% Fuquay-Varina, NC % you still wander the fields of your > %%% 919-577-9882 % sorrow." > %%%% <y...@ieee.org> % '21st Century Man', *Time*, ELOhttp://home.earthlink.net/~yatescrThat's great. Good fun but I would have thought that an advanced Alien culture would have used sub-space technology! Seriously though - I meant the measurement of quantum states http://eve.physics.ox.ac.uk/NewWeb/Research/communication/communication.html Cheers
Reply by ●June 18, 20072007-06-18
gyansorova@gmail.com writes:> Seriously though - I meant the measurement of quantum states > > http://eve.physics.ox.ac.uk/NewWeb/Research/communication/communication.htmlHuh? I mean, I've heard of quantum communication, but what has that got to do with your inquiry? -- % Randy Yates % "My Shangri-la has gone away, fading like %% Fuquay-Varina, NC % the Beatles on 'Hey Jude'" %%% 919-577-9882 % %%%% <yates@ieee.org> % 'Shangri-La', *A New World Record*, ELO http://home.earthlink.net/~yatescr
Reply by ●June 19, 20072007-06-19
On Jun 19, 2:26 pm, Randy Yates <y...@ieee.org> wrote:> gyansor...@gmail.com writes: > > Seriously though - I meant the measurement of quantum states > > >http://eve.physics.ox.ac.uk/NewWeb/Research/communication/communicati... > > Huh? I mean, I've heard of quantum communication, but what has that got to do with > your inquiry? > -- > % Randy Yates % "My Shangri-la has gone away, fading like > %% Fuquay-Varina, NC % the Beatles on 'Hey Jude'" > %%% 919-577-9882 % > %%%% <y...@ieee.org> % 'Shangri-La', *A New World Record*, ELOhttp://home.earthlink.net/~yatescrNo offence - I just thought that after I looked at that web page that maybe they are looking in the wrong place with the wrong technology. We have had comms for just over 100 year from the early days of Marconi - not very long. Mybe after another 500 years e/m comms will be long forgotten and become as extinct as cassette tapes. (are nearly!)
Reply by ●June 19, 20072007-06-19
On Mon, 18 Jun 2007 21:52:43 -0400, Randy Yates <yates@ieee.org> wrote:>gyansorova@gmail.com writes: > >> On Jun 19, 12:26 pm, Randy Yates <y...@ieee.org> wrote: >>> gyansor...@gmail.com writes: >>> > We are often told that our earliest TV and radio signals are out there >>> > in space travelling at the speed of light. But doesn't the power go >>> > down by the inverse square law? Also what about additive noise? Surely >>> > if anybody 60 light years away was to listen they would hear only >>> > noise? >>> >>> > W.King >>> >>> Hi W.King, >>> >>> Yes, the power goes down by the inverse square law. However, power alone >>> doesn't dictate receivability. What also matters is the bandwidth and >>> the noise temperature of the receiver, which can be made arbitrarily >>> small. >>> >>> Notice also that there is no "additive noise" in space except for >>> blackbody radiation, and that depends on where your receive antenna >>> is looking. Otherwise the noise is set by the noise temperature of >>> the receiver's front-end. >>> -- >>> % Randy Yates % "Bird, on the wing, >>> %% Fuquay-Varina, NC % goes floating by >>> %%% 919-577-9882 % but there's a teardrop in his eye..." >>> %%%% <y...@ieee.org> % 'One Summer Dream', *Face The Music*, ELOhttp://home.earthlink.net/~yatescr >> >> >> So has anybody done the Maths - say 60 light years at the power output >> from a typical National Radio station of the time. Would have been AM >> with a bandwidth say 5kHz. > >http://www.satsig.net/seticalc.htmHehe...I finagled the following out of it: Alien transmit frequency GHz = 0.200 Alien transmit antenna diameter m = 0.86 Alien transmit antenna gain dBi =3.14 Alien transmit power W = 1000000 Alien transmit EIRP dBW = 63.14 Receive antenna diameter m = 50 Receive system noise temperature(antenna+LNA) K = 10 Receive antenna gain dBi = 38.53 Receive antenna G/T dB/K = 28.53 Bandwidth Hz = 5000 Required overall link carrier to noise ratio C/N dB = 3 Path (spreading) loss dB = 280.28 Range km = 12284502309.787057 Range AU (1AU=Earth to Sun distance) = 82.11565715098301 Range light seconds = 40948.341032623524 Range light minutes = 682.4723505437254 Range light years = 0.0012985731828527545 Since the SETI thing is geared toward us hearing aliens, the terms are swapped, i.e., I set the "alien transmit" parameters for an imaginary terrestrial broadcast and set the receive parameters to what the aliens might be using (optimistically). So, with some pretty optimistic assumptions, like 1MW output power through a 3dBi antenna and only 5kHz transmit bandwidth (i.e., a truly gnarly AM broadcast) at 200MHz. The alien civilization using a 50m dish, which would have to be pretty carefully pointed right at earth, and a receiver cooled to 10 degrees Kelvin, they'd have to be within 0.0013 light years to have a hope of receiving it. In other words, NO, there aren't any aliens listening to Amos and Andy or the Bee Gees or anything else that'll make them want to come and kill us. 0.0013 light years is less than half a day of propagation delay...so they'd have to be close enough to be listening to Rush Limbaugh or the presidential debates or the latest about Paris Hilton's jail time to decide that we have to be destroyed. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by ●June 19, 20072007-06-19
Eric Jacobsen wrote:> On Mon, 18 Jun 2007 21:52:43 -0400, Randy Yates <yates@ieee.org> > wrote: > >> gyansorova@gmail.com writes: >> >>> On Jun 19, 12:26 pm, Randy Yates <y...@ieee.org> wrote: >>>> gyansor...@gmail.com writes: >>>>> We are often told that our earliest TV and radio signals are out there >>>>> in space travelling at the speed of light. But doesn't the power go >>>>> down by the inverse square law? Also what about additive noise? Surely >>>>> if anybody 60 light years away was to listen they would hear only >>>>> noise? >>>>> W.King >>>> Hi W.King, >>>> >>>> Yes, the power goes down by the inverse square law. However, power alone >>>> doesn't dictate receivability. What also matters is the bandwidth and >>>> the noise temperature of the receiver, which can be made arbitrarily >>>> small. >>>> >>>> Notice also that there is no "additive noise" in space except for >>>> blackbody radiation, and that depends on where your receive antenna >>>> is looking. Otherwise the noise is set by the noise temperature of >>>> the receiver's front-end. >>>> -- >>>> % Randy Yates % "Bird, on the wing, >>>> %% Fuquay-Varina, NC % goes floating by >>>> %%% 919-577-9882 % but there's a teardrop in his eye..." >>>> %%%% <y...@ieee.org> % 'One Summer Dream', *Face The Music*, ELOhttp://home.earthlink.net/~yatescr >>> >>> So has anybody done the Maths - say 60 light years at the power output >>> from a typical National Radio station of the time. Would have been AM >>> with a bandwidth say 5kHz. >> http://www.satsig.net/seticalc.htm > > > Hehe...I finagled the following out of it: > > Alien transmit frequency GHz = 0.200 > Alien transmit antenna diameter m = 0.86 > Alien transmit antenna gain dBi =3.14 > Alien transmit power W = 1000000 > Alien transmit EIRP dBW = 63.14 > Receive antenna diameter m = 50 > Receive system noise temperature(antenna+LNA) K = 10 > Receive antenna gain dBi = 38.53 > Receive antenna G/T dB/K = 28.53 > Bandwidth Hz = 5000 > Required overall link carrier to noise ratio C/N dB = 3 > Path (spreading) loss dB = 280.28 > Range km = 12284502309.787057 > Range AU (1AU=Earth to Sun distance) = 82.11565715098301 > Range light seconds = 40948.341032623524 > Range light minutes = 682.4723505437254 > Range light years = 0.0012985731828527545 > > Since the SETI thing is geared toward us hearing aliens, the terms are > swapped, i.e., I set the "alien transmit" parameters for an imaginary > terrestrial broadcast and set the receive parameters to what the > aliens might be using (optimistically). > > So, with some pretty optimistic assumptions, like 1MW output power > through a 3dBi antenna and only 5kHz transmit bandwidth (i.e., a truly > gnarly AM broadcast) at 200MHz. The alien civilization using a 50m > dish, which would have to be pretty carefully pointed right at earth, > and a receiver cooled to 10 degrees Kelvin, they'd have to be within > 0.0013 light years to have a hope of receiving it. > > In other words, NO, there aren't any aliens listening to Amos and Andy > or the Bee Gees or anything else that'll make them want to come and > kill us. 0.0013 light years is less than half a day of propagation > delay...so they'd have to be close enough to be listening to Rush > Limbaugh or the presidential debates or the latest about Paris > Hilton's jail time to decide that we have to be destroyed.Well, if they pick up the Bee Gees and want to kill us, maybe the prospect of bringing up children to be like Paris Hilton will keep them away. There must be some good that can come of her. Steve
Reply by ●June 19, 20072007-06-19
Eric Jacobsen wrote: (snip)>>http://www.satsig.net/seticalc.htm> Hehe...I finagled the following out of it:> Alien transmit frequency GHz = 0.200 > Alien transmit antenna diameter m = 0.86 > Alien transmit antenna gain dBi =3.14 > Alien transmit power W = 1000000 > Alien transmit EIRP dBW = 63.14 > Receive antenna diameter m = 50 > Receive system noise temperature(antenna+LNA) K = 10 > Receive antenna gain dBi = 38.53 > Receive antenna G/T dB/K = 28.53 > Bandwidth Hz = 5000 > Required overall link carrier to noise ratio C/N dB = 3 > Path (spreading) loss dB = 280.28 > Range km = 12284502309.787057 > Range AU (1AU=Earth to Sun distance) = 82.11565715098301 > Range light seconds = 40948.341032623524 > Range light minutes = 682.4723505437254 > Range light years = 0.0012985731828527545Pretty neat, but there is no option for FM. I used to know the number, I believe called FM advantage, that indicated the improvement in S/N ratio due to FM. That is, how much better the S/N ratio is from the output of the FM demodulator to that of the input. I remember this being described in the context of C band satellite TV, where five watts of power per TV channel can cover much of the US. I believe, then, that an FM signal with similar power would be receivable over a much greater distance. -- glen
Reply by ●June 19, 20072007-06-19
On Jun 19, 5:11 am, glen herrmannsfeldt <g...@ugcs.caltech.edu> wrote:> Eric Jacobsen wrote: > > (snip) > > > > > > >>http://www.satsig.net/seticalc.htm > > Hehe...I finagled the following out of it: > > Alien transmit frequency GHz = 0.200 > > Alien transmit antenna diameter m = 0.86 > > Alien transmit antenna gain dBi =3.14 > > Alien transmit power W = 1000000 > > Alien transmit EIRP dBW = 63.14 > > Receive antenna diameter m = 50 > > Receive system noise temperature(antenna+LNA) K = 10 > > Receive antenna gain dBi = 38.53 > > Receive antenna G/T dB/K = 28.53 > > Bandwidth Hz = 5000 > > Required overall link carrier to noise ratio C/N dB = 3 > > Path (spreading) loss dB = 280.28 > > Range km = 12284502309.787057 > > Range AU (1AU=Earth to Sun distance) = 82.11565715098301 > > Range light seconds = 40948.341032623524 > > Range light minutes = 682.4723505437254 > > Range light years = 0.0012985731828527545 >Yes, as our communications technology advances, our transmitted signals look more and more like white noise. Many digital modulation methods today look like white noise on the spectrum analyzer. Some day we will discover that the Sun is actually a gigantic alien transmitter and that "sunlight" is actually a highly advanced form of modulation. You know we can already detect some patterns in the emissions from the Sun. Think about the sunspot cycle. Have fun Mark
