# Measuring Distance with Time

Chipper Q
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### RE: And what if a gravity

Message 13935 in response to message 13933

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And what if a gravity wave(s) passed us and distorted the array (as it does LIGO... but the "arms" in this case are MUCH larger)... what would happen to the reference "radio astronomy" image as the wave passed, and could cyclic properties (like pulsar) be measured in the image variations from the reference?

Very astute, barkster!

The SKA would actually be sensitive to GWs at frequencies ~nHz, thus complementing the freqs accessible to Advanced LIGO (~100Hz) and LISA (~mHz). [See this SKA Astronomer Menu Page and click the “SKA Science” link, followed by the "Strong field tests of gravity using pulsars and black holes " link, for more details.]

MarkF
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### RE: 1. A fraction of the

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1. A fraction of the wavelength of "low freq" GR is well within GPS error... Is it not?

GPS with WAS is good to about a meter. Clocks synchronized to the WWV signals are good to about a millisecond.
A wave length of one meter corresponds to about 300Mhz
A millisecond period corresponds to 1Khz or about 300km.
If you could capture the time off the GPS. You would still be restricted signals below 300Mhz.

barkster
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### Chipper Q... RE: Very

Message 13937 in response to message 13935

Chipper Q...

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Very astute, barkster!

Thanks for the wonderful confirmation on my college academic struggle. I manage to squeeze a good one out every now and then. (Call the Nobel Commitee!)

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The SKA would actually be sensitive to GWs at frequencies ~nHz, thus complementing the freqs accessible to Advanced LIGO (~100Hz) and LISA (~mHz). [See this SKA Astronomer Menu Page and click the “SKA Science” link, followed by the "Strong field tests of gravity using pulsars and black holes " link, for more details.]

I did also see those web pages. Once again, beaten to the punch by a Microsoft protege! (Cancel that call...)

Mark...

Quote:
GPS with WAS is good to about a meter. Clocks synchronized to the WWV signals are good to about a millisecond.
A wave length of one meter corresponds to about 300Mhz
A millisecond period corresponds to 1Khz or about 300km.
If you could capture the time off the GPS. You would still be restricted signals below 300Mhz.

Thanks also... I was too lazy in the wee hours of the morning to do the math.

I'm an electronic warfare guy, vice astronomy... What's a typical freq range for radio astronomy? I thought I wanted to be below 300 MHz. Maybe use an older 3 meter TV dish? That (and GPS w/WAS) would take care of #1, no?

Timing problem?... you got me stumped on that one.

"No, I'm not a scientist... but I did stay at a Holiday Inn Express."

MarkF
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### RE: What's a typical freq

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What's a typical freq range for radio astronomy? I thought I wanted to be below 300 MHz.

The "SETI's Allen Telescope Array" mentioned earlier in this thread specifies a lower limit of 500 Mhz.
A GPS trceiver can provide both position and time. If I remember correctly standard GPS is good to 20 meters and the time would be good to about 20/300000000 or 7*10^-8 seconds. I don't know if WAS would allow correcting the time to same extent as it does the position.

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Timing problem?... you got me stumped on that one.

I don't understand.

barkster
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### RE: RE: Timing

Message 13939 in response to message 13938

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Quote:
Timing problem?... you got me stumped on that one.

I don't understand.

As in I can't come up with another "Wal-Mart" class solution to the problem at the moment. At least not until I open up another 6 pack or bottle of Jameson. :-)

"No, I'm not a scientist... but I did stay at a Holiday Inn Express."

MarkF
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Claude Shannon showed that in order to reproduce a signal you must sample it at twice the inverse of its frequency.
I hope this helps.

Czar Brent
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### RE: I'm an electronic

Message 13941 in response to message 13937

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I'm an electronic warfare guy

3 cheers for EW!!! I was a RF and IR tech in ECM.

On that note. If I understood correctly a GW is not an electromagnetic wave but more of a wave of "effect" so I dont think it could measured using our dish-TV's. Somebody stop me if Im wrong. Going back to the rubber sheet example of gravity if you were to drop a ball onto the sheet the effects would be felt everywhere almost instantanously (probably even faster than the speed of light) since its an effect and not an object.

WARNING! DiHydrogen MonOxide kills!

Chipper Q
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### About the timing, and some of

About the timing, and some of the hardware --

This link to the FAA Satellite Navigation page covering GPS basics (including Wide and Local Area Augmentation Systems) may be helpful – as Mark pointed out (above), timing's included, and positioning's good to almost a meter.

Here's a link to a page on installing a satellite TV tracking system with general info on dishes and related hardware.

Chipper Q
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### RE: On that note. If I

Message 13943 in response to message 13941

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On that note. If I understood correctly a GW is not an electromagnetic wave but more of a wave of "effect" so I dont think it could measured using our dish-TV's. Somebody stop me if Im wrong. Going back to the rubber sheet example of gravity if you were to drop a ball onto the sheet the effects would be felt everywhere almost instantanously (probably even faster than the speed of light) since its an effect and not an object.

Since a charge in motion causes an EM wave, it takes a mass in motion to cause a GW. This is hard to visualize with the rubber sheet example (although that analogy does help to show how gravitational lensing works). To see how the effects between EM waves and GWs differ, click on this link: Electromagnetic Waves versus Gravitational Waves

Physicists call these effects “forces”, and according to Einstein (and GR), not even these effects can propagate faster than the speed of light.

As for the satellite TV, if you click on the link (mentioned above) to the Square Kilometer Array (SKA), you'll see how an array of dish antennas, used primarily for radio astronomy, is also sensitive to gravitational wave radiation. barkster was asking about the feasibility of a “dish@home” collaboration.

barkster
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### RE: If I understood

Message 13944 in response to message 13943

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If I understood correctly a GW is not an electromagnetic wave but more of a wave of "effect"...

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True on both counts.

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so I dont think it could measured using our dish-TV's.

The dish antennas wouldn't detect GW directly... In "my own little TV dish (dinner) world", they would create an reference RF image which would be disturbed by GW as the waves cross the Dish@home array. Detection of GW would be in the measurement of the disturbance from reference state. Using LIGO's simplest explanation... measuring constructive/destructive interference of laser beams... I think it operates basically on the same process model.

____________ No detection _____________ Detection

LIGO ________ Perfect destructive _______ "visible" interference
____________ interference _____________ patterns

Dish@home __ Razor sharp undisturbed __ "Measurably" distorted or
____________ reference RF image _______ blurred RF image

Thoughts???

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I did also see those web pages. Once again, beaten to the punch by a Microsoft protege!

Ooops... wrong array... I was thinking of the Allen array when I typed that. Apologies to the Dutch for associating you with Microsoft.

(... and apologies to Revolution, for I have seriously hi-jacked his thread with my wishful blogging. I'm moving the dish@home discussion to this thread)

"No, I'm not a scientist... but I did stay at a Holiday Inn Express."