What is the highest radio frequency used for radio astronomy?

On 2007-09-05, Per Erik Jorde wrote:
(Paul Schlyter) writes:

...except that VHF television is vanishing. In Sweden, the very last
VHF TV transmitters will close down this fall - most of them already
have closed down. After that, we only have digital UHF television.
Other European countries are expected to do the same within a few
years.

More problematically: digital transmissions (TV or radio) have delays in
them that makes the time signal unreliable. Where to get reliable
time signals for time-critical observations (astrometry, occultation
timings, etc.) from now on?

There are a number of methods. The speaking clock is usually pretty
good. You appear to be in Norway, and while I'm not about it there,
it's good to within 5 ms from a landline here in the UK. That's
basically as accurate you're going to get unless you're timing things
automatically in some manner.

GPS will give you a precision time signal the world over.

Finally, in Norway you should be able to get decent ground-wave
reception of the MSF time/frequency signal broadcast from here in
the UK. Probably the German equivalent to, whose name I forget
right now. They can be obtained from fairly cheap radio-controlled
clocks. If you need better time accuracy than simply observing
the correct time yourself, it's relatively easy to decode these
signals automatically and connect that to whatever is recording
events.

--
Andrew Smallshaw

Chris L. Peterson wrote:

If you need to make time critical observations, you should be using GPS.
It's much more accurate than any of the radio time standards, and has a
much more widely accessible signal. GPS time receivers have become
fairly common and inexpensive (still a little more than a cheap radio
receiver, but not much).

I don't know about being much more accurate than *any* of the radio
time standards. WWV comes directly without any time delay, so it should
be quite accurate. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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On Wed, 05 Sep 2007 14:58:09 -0500, David Knisely
wrote:

I don't know about being much more accurate than *any* of the radio
time standards. WWV comes directly without any time delay, so it should
be quite accurate. Clear skies to you.

WWV is generally accurate to the tens of millisecond range. To use it
well, you need to compensate for your distance from the transmitter as
well as for various atmospheric conditions.

GPS can be accurate to the nanosecond range, with inexpensive GPS
receivers normally guaranteeing their time output to better than one
microsecond.

GPS is definitely the way to go for critical timing applications (such
as timestamping individual video frames).

_________________________________________________

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

In article ,
Chris L Peterson wrote:
On Wed, 05 Sep 2007 14:58:09 -0500, David Knisely
wrote:

I don't know about being much more accurate than *any* of the radio
time standards. WWV comes directly without any time delay, so it should
be quite accurate. Clear skies to you.

WWV is generally accurate to the tens of millisecond range. To use it
well, you need to compensate for your distance from the transmitter as
well as for various atmospheric conditions.

GPS can be accurate to the nanosecond range, with inexpensive GPS
receivers normally guaranteeing their time output to better than one
microsecond.

GPS is definitely the way to go for critical timing applications (such
as timestamping individual video frames).

Unless you have an extremely high video frame rate, the 10 ms accuracy
of WWV ought to be sufficient. At 30 frames/s there is some 33 ms
between each frame, and at 25 frames/s there is 40 ms between each
frame. No need for nanosecond accuracy here!

_______________________________________________ __

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


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

In article ,
David Knisely wrote:

Chris L. Peterson wrote:

If you need to make time critical observations, you should be using GPS.
It's much more accurate than any of the radio time standards, and has a
much more widely accessible signal. GPS time receivers have become
fairly common and inexpensive (still a little more than a cheap radio
receiver, but not much).

I don't know about being much more accurate than *any* of the radio
time standards. WWV comes directly without any time delay, so it should
be quite accurate. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

A radio wave travels some 300 meters (1000 feet) in one microsecond.
So if you're closer than 300 meter to the nearest WWV transmitter, you
might be able to talk about "no delay". Most people have hundreds of
kilometers (or more) to the nearest WWV transmitter - which means the
radio wave propagation will cause a delay of hundreds of microseconds.

The radio waves from the GPS satellites will of course also need time
to propagate. But the GPS receiver will know the precise distance to
each satellite (otherwise it would be unable to figure out its precise
position), and is therefore able to compensate for this delay, giving
you a more precise time to an accuracy of one microsecond or so.
That's why GPS time is more accurate than any of the radio time signals.

Of course if you only need a modest time accuracy of some 100
milliseconds, then you can accept the delay from radio wave
propagation over 10,000 or 20,000 km without any problem. And 20,000
km, that's halfway around the globe.

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

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.

On Wed, 05 Sep 2007 21:12:57 GMT, (Paul Schlyter) wrote:

Unless you have an extremely high video frame rate, the 10 ms accuracy
of WWV ought to be sufficient. At 30 frames/s there is some 33 ms
between each frame, and at 25 frames/s there is 40 ms between each
frame. No need for nanosecond accuracy here!

With the ordinary video cameras used in my allsky network, a subframe
exposure (derived from a deinterlaced frame) is 16 ms. By interpolating
brightness, I can usually estimate the event start time to about 4 ms.
To eliminate any timing error, I therefore require my timestamp accuracy
to be about 2 ms, and I need that accuracy to be fixed (and my times
synchronized) across multiple stations separated by hundreds of
kilometers. What is actually recorded is the individual frame start and
stop times to an accuracy of 1 ms. I don't need the full microsecond
accuracy of my GPS clocks, but I need much better than I can easily get
with a radio standard.

_________________________________________________

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

"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).

Yes I think top-posting is the way to go these days, a normal PC screen
holds alot more text than in the old days, and people reply to specific
topics so the people already know what it's all about, and if I reply
to a specific question I'll quote that one ,so kill me

Actually (not complaining - just noting for those who don't know) you
can also receive single meteors entering the atmosphere,
not only meteor shower.
Tuning the SSB radio to a tv carrier far far away will give you a 'ping'
every time a meteor hits between you and the station, the farther away
the more pings you get.

http://www.gravitywell.org/misc/misc.htm
to show you what it sounds like (no I'm not a webdesigner either

To the best of my knowledge the station I'm tuned in on is in the baltic,
and I live in Sweden, so across the entire baltic sea I get to hear alot of
pings... I also have a feeling they'll continue using analogue tv for a while.

This happens with television too. VHF signals can reflect
off other things too, like auroras and patches of intense
ionization in the E layer ("E Layer Skip"). Sporadic E
signals can be extremely strong.

...except that VHF television is vanishing. In Sweden, the very last
VHF TV transmitters will close down this fall - most of them already
have closed down. After that, we only have digital UHF television.
Other European countries are expected to do the same within a few
years.

And UHF signals don't reflect as well off sporadic E layes.

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

//Greger
Project Argus station JO89sn
Bålsta - SWEDEN

The problem with top posting is the respondent doesn't actually
need to read what you said.


--


'we establish by definition that the "time" required by
light to travel from A to B equals the "time" it requires
to travel from B to A' because I SAY SO and you have to
agree because I'm the great genius, STOOOPID, don't you
dare question it. -- Rabbi Albert Einstein

http://www.androcles01.pwp.blueyonde...rt/tAB=tBA.gif

'we establish by definition that the "time" required by
light to travel from A to B doesn't equal the "time" it requires
to travel from B to A in the stationary system, obviously.' --
Heretic Jan Bielawski, assistant light-bulb changer.

Ref: ups.com


"SR is GR with G=0." -- Uncle Stooopid.

The Uncle Stooopid doctrine:
http://sound.westhost.com/counterfeit.jpg

"What can be asserted without evidence can also be dismissed without
evidence." -- Uncle Stooopid.


"Counterfactual assumptions yield nonsense.
If such a thing were actually observed, reliably and reproducibly, then
relativity would immediately need a major overhaul if not a complete
replacement." -- Humpty Roberts.

Rabbi Albert Einstein in 1895 failed an examination that would
have allowed him to study for a diploma as an electrical engineer
at the Eidgenössische Technische Hochschule in Zurich
(couldn't even pass the SATs).

According to Phuckwit Duck it was geography and history that Einstein
failed on, as if Eidgenössische Technische Hochschule would give a
damn. That tells you the lengths these lying *******s will go to to
protect their tin god, but its always a laugh when they slip up.
Trolls, the lot of them.

"This is PHYSICS, not math or logic, and "proof" is completely
irrelevant." -- Humpty Roberts.






"Greg" wrote in message
...
: Yes I think top-posting is the way to go these days, a normal PC screen
: holds alot more text than in the old days, and people reply to specific
: topics so the people already know what it's all about, and if I reply
: to a specific question I'll quote that one ,so kill me
:
: Actually (not complaining - just noting for those who don't know) you
: can also receive single meteors entering the atmosphere,
: not only meteor shower.
: Tuning the SSB radio to a tv carrier far far away will give you a 'ping'
: every time a meteor hits between you and the station, the farther away
: the more pings you get.
:
: http://www.gravitywell.org/misc/misc.htm
: to show you what it sounds like (no I'm not a webdesigner either
:
: To the best of my knowledge the station I'm tuned in on is in the baltic,
: and I live in Sweden, so across the entire baltic sea I get to hear alot
of
: pings... I also have a feeling they'll continue using analogue tv for a
while.
:
: This happens with television too. VHF signals can reflect
: off other things too, like auroras and patches of intense
: ionization in the E layer ("E Layer Skip"). Sporadic E
: signals can be extremely strong.
:
: ...except that VHF television is vanishing. In Sweden, the very last
: VHF TV transmitters will close down this fall - most of them already
: have closed down. After that, we only have digital UHF television.
: Other European countries are expected to do the same within a few
: years.
:
: And UHF signals don't reflect as well off sporadic E layes.
:
: --
: ----------------------------------------------------------------
: Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
: e-mail: pausch at stockholm dot bostream dot se
: WWW: http://stjarnhimlen.se/
:
: //Greger
: Project Argus station JO89sn
: Bålsta - SWEDEN
:
: