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#21
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What is the highest radio frequency used for radio astronomy?
On Aug 30, 11:42 pm, (Paul Schlyter) wrote:
In article om, laura halliday wrote: The usual agreement is that it's radio astronomy when the incoming signals are electronically detected (e.g. diodes) and processed. It's optical/infrared astronomy when the incoming signals are measured by a bolometer or other non-electronic means. There is, naturally, some crossover. Given today's CCD chips which indeed are electronic devices, does that mean todays optical telescopes, with CCD chips which detect light electronically, have become radio telescopes? Can't say I agree with that; CCDs count photons, which makes them a lot closer to bolometers than diodes. The other issue, of course, is just what difference it makes. Astronomers examine the universe to see how it works. They use various wavelengths to do it. Laura Halliday VE7LDH "Non sequitur. Your ACKS are Grid: CN89mg uncoordinated." ICBM: 49 16.05 N 122 56.92 W - Nomad the Network Engineer |
#22
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What is the highest radio frequency used for radio astronomy?
On Fri, 31 Aug 2007 08:01:21 -0700, laura halliday
wrote: Can't say I agree with that; CCDs count photons, which makes them a lot closer to bolometers than diodes. That's an interesting observation. In the submillimeter domain we are just entering the (high) range of EM frequencies where our instruments detect quanta. Below that they are wave detectors. I don't think we have any technology that allows us to detect photons in the radio band, for instance. The other issue, of course, is just what difference it makes. In terms of astronomy, it makes no difference at all. It is interesting in terms of language, however. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
#23
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What is the highest radio frequency used for radio astronomy?
On Aug 30, 4:33 am, gwatts wrote:
Radium wrote: Hi: What is the highest radio frequency used for radio astronomy? According to the link below, it is 3438 GHz: http://books.nap.edu/openbook.php?re...=11719&page=11 Is 3438 GHz the highest radio frequency used for radio astronomy? If you read on a little farther you'll find 'blurring the distinction between radio astronomy and infrared astronomy.' So where do you want to draw the line between radio astronomy and infrared astronomy? There's you're answer. Sorry, I meant to ask whether 3,438 GHz is the highest radio frequency used to receive audio signals from outer space. I should have made my question more specific. Radio-astronomers study sounds from the sun as well as visual data. I wonder if a space station with a 3,438 GHz AM receiver could pick up any extremely-distant audio signals between 20 to 20,000 Hz [from magnetars, gamma-ray-bursts, supernovae and other high-energy but cosmic objects] after demodulating the 3,438 GHz AM carrier wave. |
#24
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What is the highest radio frequency used for radio astronomy?
In article .com,
Radium wrote: Sorry, I meant to ask whether 3,438 GHz is the highest radio frequency used to receive audio signals from outer space. I should have made my question more specific. Radio-astronomers study sounds from the sun as well as visual data. Radio astronomers study EM radiation, not "sounds", from the Sun. Since there's a vacuum between the Sun and us, no sound waves would be able to propagate from the Sun to us. Otoh careeful studies of Doppler shifts have enabled solar astronomers to study sound waves *within* the Sun. But these sound waves never reach us - we can only study them indirectly because they move matter near the solar surface. And their frequencies are usually well below what the human ear can hear, i.e. it's infrasound. I wonder if a space station with a 3,438 GHz AM receiver could pick up any extremely-distant audio signals between 20 to 20,000 Hz [from magnetars, gamma-ray-bursts, supernovae and other high-energy but cosmic objects] after demodulating the 3,438 GHz AM carrier wave. They could certainly try .... but if they did, and succeeded, it would sound just like noise. This radiation does not originate as audio signals, and they're certainly not put on an AM modulated carrier. Therefore it's hardly useful to try to demodulate these waves as if they were AM modulated signals - there's e.g. no AM carrier (i.e. one single frequency which is stronger than all the others within the frequency band). Also, any audio (= pressure waves within a gas) which are formed outside the Earth is certainly *not* limited to the 20 to 20,000 Hz frequency range..... that frequency range is merely the limits of what the human ear can hear. -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
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What is the highest radio frequency used for radio astronomy?
On Sep 1, 1:12 am, (Paul Schlyter) wrote:
In article .com, Radium wrote: Sorry, I meant to ask whether 3,438 GHz is the highest radio frequency used to receive audio signals from outer space. I should have made my question more specific. Radio-astronomers study sounds from the sun as well as visual data. Radio astronomers study EM radiation, not "sounds", from the Sun. Since there's a vacuum between the Sun and us, no sound waves would be able to propagate from the Sun to us. The radio-frequency EM radiation emitted from the sun does translate to sound when it is picked up by a radio receiver of the same carrier frequency. Otoh careeful studies of Doppler shifts have enabled solar astronomers to study sound waves *within* the Sun. But these sound waves never reach us - we can only study them indirectly because they move matter near the solar surface. And their frequencies are usually well below what the human ear can hear, i.e. it's infrasound. That's why audio software is often used to speed up the infrasound until it is at least 20 Hz so that humans can hear it. I wonder if a space station with a 3,438 GHz AM receiver could pick up any extremely-distant audio signals between 20 to 20,000 Hz [from magnetars, gamma-ray-bursts, supernovae and other high-energy but cosmic objects] after demodulating the 3,438 GHz AM carrier wave. They could certainly try .... but if they did, and succeeded, it would sound just like noise. This radiation does not originate as audio signals, and they're certainly not put on an AM modulated carrier. Well, most natural sources of EMI and RFI are amplitude-modulated. The audio signals are not put on the carrier wave, however if the variations in the peak-to-peak amplitude of the 3,438 GHz electromagnetic waves correspond to frequencies between 20 and 20,000 Hz [and the peak-to-peak variations are sufficient in power], then the signal can be picked up of 3,438 GHz receiver and demodulated. The result would be audio signals. Therefore it's hardly useful to try to demodulate these waves as if they were AM modulated signals - there's e.g. no AM carrier (i.e. one single frequency which is stronger than all the others within the frequency band). Also, any audio (= pressure waves within a gas) which are formed outside the Earth is certainly *not* limited to the 20 to 20,000 Hz frequency range..... that frequency range is merely the limits of what the human ear can hear. Audio waves from 20 to 20,000 Hz can be derived from demodulating radio waves. Since most natural radio disruptions are amplitude- modulated it would be easier to listen to cosmic sounds using an AM receiver as opposed to an FM receiver. FM is immune to the disruptions that normally affect AM. In AM demodulation: 1. The amplitude of the demodulated signal [what we hear] is determined by the depth-of-change of the peak-to-peak amplitude of the radio wave. If the peak-to-peak amplitude of the radio wave is above the central amplitude** then the demodulated signal will have a positive voltage. If the peak-to-peak amplitude of the radio wave is below the central amplitude then the demodulated signal will have a negative voltage. If these changes in voltages are between 20 and 20,000 Hz*, then they will be audible if the over voltage is high- enough and this signal is fed into a loudspeaker 2. The frequency of the demodulated signal is determined by the rate- of-change of the peak-to-peak amplitude of the radio wave *In an electric signal, a cycle is when a voltage changes from zero to positive to zero to negative and then back to zero. In USA, the power supply is 60 Hz [cycles per second] while being 50 Hz in Europe. In order to produce audible sound when fed to a loudspeaker, the peak-to- peak voltage must be high-enough to reach the threshold of hearing or above and must be at least 20 Hz but no more than 20,000 Hz. A loudspeaker produces the mechanical equivalent of the electric signal it receives. ** Central amplitude = amplitude of the radio wave when there is no modulation signal. |
#26
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What is the highest radio frequency used for radio astronomy?
In article .com,
Radium wrote: On Sep 1, 1:12 am, (Paul Schlyter) wrote: In article .com, Radium wrote: Sorry, I meant to ask whether 3,438 GHz is the highest radio frequency used to receive audio signals from outer space. I should have made my question more specific. Radio-astronomers study sounds from the sun as well as visual data. Radio astronomers study EM radiation, not "sounds", from the Sun. Since there's a vacuum between the Sun and us, no sound waves would be able to propagate from the Sun to us. The radio-frequency EM radiation emitted from the sun does translate to sound when it is picked up by a radio receiver of the same carrier frequency. Here you make the silent assumption that the electric signal from the radio receiver is fed to a loudspekarer. But that's just *one* possible way of converting the EM radiation. You could use other ways too. For instance displaying it on some video screen - those who do so could claim that "The radio-frequency EM radiation emitted from the sun does translate to light when it is picked up by a radio receiver of the same carrier frequency" (with the silent assupmtion that the output from the receiver is displayed on a video screen). It's the translator who decides what the EM radiation translates to.... Btw did you ever try to *listen* to a TV transmission? I mean, to feed the *video* signal (not the audio signal) to a loudspeaker instead of a video screen? Yep, the sound changes with the contents of the picture - but of course one hears only the lowermost part of the 5 MHz of bandwidth a normal video signal has. Another interesting experience is to feed a digital signal directly to a loudspeaker instead of decoding and converting it to an analog signal first. That of course requires that the digital signal is within the audible range of frequencies -- the signal from a traditional telephone modem would be quite suitable here. The old 300 bps modems produced a signal with a quite clear structure (the signal jumped between two frequencies 300 times per second), but the more modern telephone modems which can handle bit rates up to 57600 bps, they sound pretty much like white noise to the human ear. Otoh careeful studies of Doppler shifts have enabled solar astronomers to study sound waves *within* the Sun. But these sound waves never reach us - we can only study them indirectly because they move matter near the solar surface. And their frequencies are usually well below what the human ear can hear, i.e. it's infrasound. That's why audio software is often used to speed up the infrasound until it is at least 20 Hz so that humans can hear it. :-) ....there's no need to speed it up just to convert the frequency into the audible range.... the frequency can be bumped up even if the original speed is maintained. I wonder if a space station with a 3,438 GHz AM receiver could pick up any extremely-distant audio signals between 20 to 20,000 Hz [from magnetars, gamma-ray-bursts, supernovae and other high-energy but cosmic objects] after demodulating the 3,438 GHz AM carrier wave. They could certainly try .... but if they did, and succeeded, it would sound just like noise. This radiation does not originate as audio signals, and they're certainly not put on an AM modulated carrier. Well, most natural sources of EMI and RFI are amplitude-modulated. They're probably frequency modulated and phase modulated as well, since their contents are pretty random. I strongly doubt they consist of one single frequency whose amplitude varies while its frequency and phase remains unchanged (that's the way a properly modulated AM signal would be). In particular it won't have symmetrical sidebands with the same content, the way a real AM signal should have. The audio signals are not put on the carrier wave, however if the variations in the peak-to-peak amplitude of the 3,438 GHz electromagnetic waves correspond to frequencies between 20 and 20,000 Hz [and the peak-to-peak variations are sufficient in power], then the signal can be picked up of 3,438 GHz receiver and demodulated. The result would be audio signals. Trivially true -- but these audio signals would be created by us humans. They're not inherent in the original signal. Therefore it's hardly useful to try to demodulate these waves as if they were AM modulated signals - there's e.g. no AM carrier (i.e. one single frequency which is stronger than all the others within the frequency band). Also, any audio (= pressure waves within a gas) which are formed outside the Earth is certainly *not* limited to the 20 to 20,000 Hz frequency range..... that frequency range is merely the limits of what the human ear can hear. Audio waves from 20 to 20,000 Hz can be derived from demodulating radio waves. You can create audio waves also below 20 Hz and above 20,000 Hz as well. Humans won't hear them, true, but dogs and bats might enjoy them... :-) Since most natural radio disruptions are amplitude- modulated it would be easier to listen to cosmic sounds These sounds aren't "cosmic" - they're created here on Earth by us humans. using an AM receiver as opposed to an FM receiver. FM is immune to the disruptions that normally affect AM. Did you ever try to tune an FM receiver between radio stations on the FM band? Also turn off any "muting" or "squelch" the receiver may have. What do you hear? Silence? Or perhaps noise? You say "FM is immune to the disruptions that normally affect AM". If this is to work, you must have an FM carrier which is strong enough for the receivers amplitude limitation circuits to work well. Cosmic radio noise is far too weak for that. description of AM and definition of frequency snipped -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/ |
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What is the highest radio frequency used for radio astronomy?
On Aug 31, 6:44 am, Chris L Peterson wrote:
On Fri, 31 Aug 2007 12:13:05 GMT, (Paul Schlyter) wrote: That's a little illogical. It's like considering a frequency slightly above 300 kHz to belong to "the Megahertz band" .... No, it's _more_ logical. It's having arbitrary names for various regions of the EM spectrum that isn't entirely logical. _________________________________________________ Chris L Peterson Cloudbait Observatoryhttp://www.cloudbait.com Most all ET signals are processed by some kind of technology, so that we can then see or hear the information contained within that signal. If the signal information is encrypted or otherwise weird, then seeing the signal is usually the better alternative. I believe 0.1 TeraHertz of 3 mm is more than good enough, as being roughly 10 fold higher in frequency than any X Band radar imaging efforts sent from Earth would ever manage to contribute all that much due to our terrestrial atmosphere and magnetosphere that'll convert and/or divert much of that outgoing and incoming X Band energy. However, a blue/violet laser cannon would likely become by far the most energy efficient and focused alternative for outgoing as well as incoming signals, especially if those efforts were getting off-world managed, such as within the nearby turf of our moon's L1 could easily accommodate. At least in that way an amateur terrestrial or ET astronomer could rather easily detect such without special instruments. There's all kinds of nifty ways for us to hear and/or see what our moon has to say. It's sodium populated atmosphere along with the surface likes of radon are worth a good deal of science about solar wind and cosmic interactions, as well as for the graviton/tidal issues associated with having to orbit Earth as well as the sun that should be responsible for keeping the low density core of our moon a little extra toasty, as a renewable geothermal cache of energy that could essentially accommodate a fairly extensive underground protected human use of our moon. - Brad Guth |
#28
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What is the highest radio frequency used for radio astronomy?
On Sep 2, 2:42 am, (Paul Schlyter) wrote:
In article .com, Radium wrote: The radio-frequency EM radiation emitted from the sun does translate to sound when it is picked up by a radio receiver of the same carrier frequency. Here you make the silent assumption that the electric signal from the radio receiver is fed to a loudspekarer. But that's just *one* possible way of converting the EM radiation. You could use other ways too. For instance displaying it on some video screen - those who do so could claim that "The radio-frequency EM radiation emitted from the sun does translate to light when it is picked up by a radio receiver of the same carrier frequency" (with the silent assupmtion that the output from the receiver is displayed on a video screen). It's the translator who decides what the EM radiation translates to.... Btw did you ever try to *listen* to a TV transmission? I mean, to feed the *video* signal (not the audio signal) to a loudspeaker instead of a video screen? Yep, the sound changes with the contents of the picture - but of course one hears only the lowermost part of the 5 MHz of bandwidth a normal video signal has. I've done this before. Plugged the video signal into the audio receiver. There is some buzzing sound. As you said, that sound changes as video signal changes. Another interesting experience is to feed a digital signal directly to a loudspeaker instead of decoding and converting it to an analog signal first. That of course requires that the digital signal is within the audible range of frequencies -- the signal from a traditional telephone modem would be quite suitable here. The old 300 bps modems produced a signal with a quite clear structure (the signal jumped between two frequencies 300 times per second), but the more modern telephone modems which can handle bit rates up to 57600 bps, they sound pretty much like white noise to the human ear. Interesting indeed. However, are those old modems really "digital"? That's why audio software is often used to speed up the infrasound until it is at least 20 Hz so that humans can hear it. :-) ....there's no need to speed it up just to convert the frequency into the audible range.... the frequency can be bumped up even if the original speed is maintained. Is this done using audio software such as Adobe Audition? Quotes from http://www.adobe.com/products/audition/overview2.html : "Time and pitch processing: Change tempo without shifting pitch - or shift pitch without changing tempo - and never introduce audio artifacts." using an AM receiver as opposed to an FM receiver. FM is immune to the disruptions that normally affect AM. Did you ever try to tune an FM receiver between radio stations on the FM band? Also turn off any "muting" or "squelch" the receiver may have. What do you hear? Silence? Or perhaps noise? White noise. Hissing. Nothing special. |
#29
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What is the highest radio frequency used for radio astronomy?
BradGuth wrote:
I believe No one cares, Brad. -- Official Overseer of Kooks and Saucerheads for alt.astronomy Wee Davie Tholen is a grade-school lamer Trainer and leash holder of: Honest "Clockbrain" John nightbat "fro0tbat" of alt.astronomy Tom "TommY Crackpotter" Potter http://www.caballista.org/auk/kookle.php?search=deco "You really are one of the litsiest people I know, Mr. Deco." --Kali, quoted endlessly by David Tholen as evidence of "something" "Why are you now discussing Art Deco, rec.music.classical, the coward using a fake name who avoids answering questions and doesn't try to discuss music with anyone?" --David Tholen "Quite a kook-out, Deco. You've been frothing even more ever since I demonstrated how you believe that ah's family name is "ah"." --David Tholen |
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What is the highest radio frequency used for radio astronomy?
In sci.astro.amateur laura halliday wrote:
The ITU definition of "radio" ends at the top of EHF, at 300 GHz. However, this is more a reflection of the technical state of the art at the time the definition was made. Earlier definitions ended at 30 GHz, or even lower. I've read papers in journals for radio equipment that operates above 400 GHz. You need a microscope to inspect the components. :-) Above 300 GHz is no man's land, in that no radio license is required to send signals. Laser communication links are not licensed as radios; they are not generally licensed at all, unless health & safety officials take an interest in the lasers themselves. Hi, Laura, and thanks to you and others very helpful responses on this point. A bit of browsing the Web has shown me that definitions can vary, for example with the portion of the submillimeter spectrum around 300 GHz - 1 THz (or 1mm - 300um) being considered as more "radio-like" by some. The spectrum between EHF and infrared is viewed as not useful for communication, because the atmosphere is more-or-less opaque at these wavelengths. But that's what they said about frequencies about 30 MHz in the 1920s, too. And in space, who cares? Exactly; and it's interesting some of the special environments which are above most of the atmosphere's water vapor, or dessicated, that are used for terrestrial observations at certain points in the EHF and submilliter spectrum. Most appreciatively, Margo Schulter Lat. 38.566 Long. -121.430 |
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