What is the highest radio frequency used for radio astronomy?

Peter Webb wrote:

"Margo Schulter" wrote in message
...
In sci.astro.amateur 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.

Hi, Radium, gwatts, and all.

I'd agree that the real question here may be where to draw the line
between radio and infrared, and thus between radio astronomy and
infrared astronomy.

What I learned about 40 years ago was that while the line wasn't
a clear one, the shortest or highest-frequency range of radio waves
traditionally placed in that classification were "millimeter waves"
with a wavelength of 1-10mm. Given that the speed of light, c, is
very close to 3 x 10^10 centimeters per second, so that a 1 cm or
10mm wave would have a frequency of around 30 Gz, this category
(also known as Extremely High Frequency or EHF) has a 30-300GHz
range.

A frequency of 3438 GHz, with a wavelength a bit shorter than
100 microns, would thus be about an order of magnitude higher
in frequency than the top of the EHF range. While I'm not sure
if there's a specific technical name for this range (analogous
to the various categories of radio waves like EHF), my first
layperson's guess would be that it could be considered very
far infrared (that is, far from the visual spectrum and close
to radio).

It's interesting question how radio and infrared astronomy are
distinguished: mainly by the nature of the waves, or also by
the apparatus used. I'd like to to learn more of this myself.

Again, I'd emphasize that in giving the range for EHF, I'm not
saying that anything above 300 GHz wouldn't be considered radio,
only mentioning this category as an example of what was
traditionally considered near the top of the radio spectrum.

Maybe Laura or others could comment more expertly on this.

Most appreciatively,

Margo Schulter

Lat. 38.566 Long. -121.430


So its your contention that the atmosphere is transparent all the way up
from microwaves to IR?

She didnt say anything at all about this. Why are you "contending"
contenacity contumaciously?

On Aug 30, 8:03 am, Margo Schulter wrote:

It's interesting question how radio and infrared astronomy are
distinguished: mainly by the nature of the waves, or also by
the apparatus used. I'd like to to learn more of this myself.

Again, I'd emphasize that in giving the range for EHF, I'm not
saying that anything above 300 GHz wouldn't be considered radio,
only mentioning this category as an example of what was
traditionally considered near the top of the radio spectrum.

Maybe Laura or others could comment more expertly on this.

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.

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?

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.

Laura Halliday VE7LDH "Non sequitur. Your ACKS are
Grid: CN89mg uncoordinated."
ICBM: 49 16.05 N 122 56.92 W - Nomad the Network Engineer

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?

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

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

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

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.

As Laura and others point out, all such definitions are somewhat
arbitrary, though I suppose the above is as good as any.

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.

If you define "radio" as employing _coherent_ detection, which I think
is what Laura is getting at here, then the limit 30 years ago was
about 3E13 Hz, i.e., 10 microns in the infrared. The limit today may
be higher; laboratory physics experiments have been done with higher
frequencies, but I'm not aware of any astronomical observations. The
technique is entirely radio-like: mix the incoming signal with a local
oscillator (laser in this case), then amplify and detect the beat
frequencies.

As others have written in response to the OP's additional query, none
of this has anything to do with amplitude modulation or sound.

"Steve" wrote in message
oups.com...
:
: 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.
:
: As Laura and others point out, all such definitions are somewhat
: arbitrary, though I suppose the above is as good as any.
:
: 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.
:
: If you define "radio" as employing _coherent_ detection, which I think
: is what Laura is getting at here, then the limit 30 years ago was
: about 3E13 Hz, i.e., 10 microns in the infrared. The limit today may
: be higher; laboratory physics experiments have been done with higher
: frequencies, but I'm not aware of any astronomical observations. The
: technique is entirely radio-like: mix the incoming signal with a local
: oscillator (laser in this case), then amplify and detect the beat
: frequencies.
:
: As others have written in response to the OP's additional query, none
: of this has anything to do with amplitude modulation or sound.

I did a living room experiment with my TV's remote control,
it seems to be adequately modulated, changing channels,
raising and lowering sound, muting and so on quite reliably.
I expect laboratory physics experiments could do it at optical
frequencies if they really tried hard (defining radio as employing
_coherent_ detection, that is).

On 30 Aug 2007 15:03:23 GMT, Margo Schulter
wrote:

A frequency of 3438 GHz, with a wavelength a bit shorter than
100 microns, would thus be about an order of magnitude higher
in frequency than the top of the EHF range. While I'm not sure
if there's a specific technical name for this range (analogous
to the various categories of radio waves like EHF), my first
layperson's guess would be that it could be considered very
far infrared (that is, far from the visual spectrum and close
to radio).

They are called submillimeter waves, and represent the transition
between what is widely accepted as "radio" and what is widely accepted
as "optical".

IMO the best way to categorize EM bands is by the nature of the
equipment we use to measure energy in those bands. Submillimeter
radiation is detected using special receivers which combine optical-like
sensors (bolometers) and radio-like sensors (heterodyne receivers and
tuned antennas). I think its best to simply consider the range from
about one millimeter to 1/10 millimeter as "submillimeter", neither
radio nor optical (IR).

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

In article ,
Chris L Peterson wrote:

IMO the best way to categorize EM bands is by the nature of the
equipment we use to measure energy in those bands. Submillimeter
radiation is detected using special receivers which combine optical-like
sensors (bolometers) and radio-like sensors (heterodyne receivers and
tuned antennas). I think its best to simply consider the range from
about one millimeter to 1/10 millimeter as "submillimeter", neither
radio nor optical (IR).

Or perhaps we could consider that wavelength band both "optical" and
"radio", since radiation at those wavelengths probably can be detected
both with radio and with optical equipment.

And if one wants to decide on some single wavelength limit between
"radio" and "optical", 0.3 millimeter appears to be a good choice
since it resides near the middle of this "submillimeter" band. This
corresponds to a frequency of one TeraHertz.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/

Paul Schlyter wrote:


And if one wants to decide on some single wavelength limit
between "radio" and "optical", 0.3 millimeter appears to be a
good choice since it resides near the middle of this
"submillimeter" band. This corresponds to a frequency of one
TeraHertz.

And in fact, e-m radiation at and around that frequency is often
called Terahertz radiation, or Terahertz waves, or T-rays, etc.
More specifically, from 300 GHz to 3 THz is the Terahertz band.
This terminology seems to be used more in non-astronomical
fields.

http://en.wikipedia.org/wiki/Terahertz

--
Dan Tilque