[time-nuts] Result of Earth Quake speeds up earth?

[Bob Camp]

Hi

Maybe I missed something here. It would hardly be the first time.

If the objective is to come up with a sub 1 ms resolution on observing the object. And we have chosen this all so indeed we get "fast" changes. Isn't a 1,000 second integration going to get in the way? If we need the integration to simply "see" the signal, then determining it's "center" within the integration time to less than 1 ppm seems unlikely. On a hand waving basis that's sort of a 60 db signal to noise.  

As I said, I may be missing something. 

Bob


On Mar 20, 2011, at 2:31 PM, Bruce Griffiths wrote:

> jimlux wrote:
>> On 3/19/11 10:41 PM, Bruce Griffiths wrote:
>>> Bruce Griffiths wrote:
>>>> jimlux wrote:
>>>>> 
>>>>>> 
>>>>>> A 10-12m diameter dish is probably close to the minimum feasible
>>>>>> aperture.
>>>>>> A 4m dish can be made to work in conjunction with a mauch larger dish
>>>>>> (eg 30m).
>>>>>> 
>>>>> 
>>>>> The original speculation was for measuring the small change in earth
>>>>> rotation rate, for which some sort of interferometric measurement of
>>>>> a stellar source could be used.
>>>>> 
>>>>> The source has to be bright (so you can detect it with a practical
>>>>> antenna.. not everyone has a 30m dish in their back yard)
>>>>> The source has to be small angle (or at least something that you
>>>>> could accurately determine the centroid of)
>>>>> The source has to be "not moving" (which I think leaves out using
>>>>> something like jupiter)
>>>>> The frequency of measurement has to be somewhere that the atmosphere
>>>>> won't dominate the uncertainty (leaving out optical, I think)
>>>>> 
>>>>> 
>>>>> SO what's the brightest small angular radio source out there?
>>>> 
>>>> 3C273
>>>> 
>>>> RA 12:29.1 DEC 02:03.1
>>> Its flux density is around 30 Jy in the waterhole region.
>>> ie about 3E-17W per square meter for a 100MHz bandwidth.
>>> The radio spectrum is relatively flat due to the synchroton nature of
>>> the blazar source.
>> 
>> 
>> Ok, so lets say our ambitious amateur has a 3 meter diameter dish.. that's about 7 square meters.  Knock that down to 4 square meters to make up for illumination and feed issues.  So we're looking at 12E-17 W
>> or 1.2E-13 mW or -130dBm, in 100 MHz BW.
>> 
>> Say we want the "signal" to be comparable to the noise power, what do we need for a noise temperature.. kTB = -130dBm.  kT = -174dBm/Hz for 300K, B = 80dBHz.   (so at room temp, kTB would be -94dBm.. we need to drop noise power by at least 40 dB, so T needs to be down in the "sub 1 K" area, which is totally impractical.
>> 
>> Looks like we need a bigger antenna..
>> Unless there's some clever correlation scheme.
>> 
>> 
>> 
>> 
>> 
> With 2 or more antennas and integration times of 100sec to 1000 sec its routine to image objects well below the thermal noise level.
> The fluctuations in the source signal correlate whereas the thermal noise in a receiver/dish pair do not.
> 
> Modeling of the relative drift and frequency (and phase) offset (even if they are hydrogen masers) of the 2 sampling clocks involved is sometimes necessary.
> 
> Bruce
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.