What is the highest radio frequency used for radio astronomy?

[laura halliday]

On Aug 30, 11:42 pm, pau...@saaf.se (Paul Schlyter) wrote:

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

[Chris L Peterson]

On Fri, 31 Aug 2007 08:01:21 -0700, laura halliday
<marsgal42@hotmail.com> wrote:


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.



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

[Radium]

On Aug 30, 4:33 am, gwatts <gwa...@frontiernet.net> 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.

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.

[Paul Schlyter]

In article <1188620214.390706.118800@r29g2000hsg.googlegroups .com>,
Radium <glucegen1@gmail.com> wrote:


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.


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/

[Radium]

On Sep 1, 1:12 am, pau...@saaf.se (Paul Schlyter) 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.


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.



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.





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.

[Paul Schlyter]

In article <1188683416.066878.250530@d55g2000hsg.googlegroups .com>,
Radium <glucegen1@gmail.com> wrote:


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.


:-) ....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.


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.


Trivially true -- but these audio signals would be created by us
humans. They're not inherent in the original signal.


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... :-)


These sounds aren't "cosmic" - they're created here on Earth by us humans.


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/

[BradGuth]

On Aug 31, 6:44 am, Chris L Peterson <c...@alumni.caltech.edu> wrote:

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

[Radium]

On Sep 2, 2:42 am, pau...@saaf.se (Paul Schlyter) wrote:





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.


Interesting indeed. However, are those old modems really "digital"?



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."



White noise. Hissing. Nothing special.

[Art Deco]

BradGuth <bradguth@gmail.com> wrote:


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

[Margo Schulter]

In sci.astro.amateur laura halliday <marsgal42@hotmail.com> wrote:

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.


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
mschulter@calweb.com
Lat. 38.566 Long. -121.430